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Genetic Effects of Radiation-Isaac Asimov, Theodosius Dobzhansky · Pilot Handbook of Aeronautical Knowledge

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Speaker 1: Preface and the authors of The Genetic Effects of Radiation.
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Speaker 1: This is a LibriVox recording. All LibriVox recordings are in
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Speaker 1: the public domain. For more information or to volunteer, please
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Speaker 1: visit LibriVox dot org. Read by Larry Wilson. The Genetic
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Speaker 1: Effects of Radiation by Isaac Asimov and Theodosius Dabjangsky preface
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Speaker 1: one of a series on understanding the atom. Nuclear energy
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Speaker 1: is playing a vital role in the life of every man, woman,
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Speaker 1: and child in the United States today. In the years ahead,
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Speaker 1: it will affect increasingly all the peoples of the Earth.
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Speaker 1: It is essential that all Americans gain an understanding of
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Speaker 1: this vital force if they are to discharge thoughtfully their
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Speaker 1: responsibilities as citizens, and if they are to realize fully
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Speaker 1: the myriad benefits that nuclear energy offers them. The United
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Speaker 1: States Atomic Energy Commission provides this booklet to help you
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Speaker 1: achieve such understanding. Edward J. Brunenkoant Director Division of Technical Information,
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Speaker 1: United States Atomic Energy Commission, Doctor Glenn T. Seborg, Chairman
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Speaker 1: James T. Raimi, doctor jal F. Tape, doctor Samuel N.
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Speaker 1: Narbut Wilford E. Johnson, the authors. Isaac Asimov received his
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Speaker 1: academic degrees from Columbia University and is Associate Professor of
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Speaker 1: Biochemistry at the Boston University School of Medicine. He is
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Speaker 1: a prolific author who has written over sixty five books
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Speaker 1: in the past fifteen years, including about twenty science fiction
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Speaker 1: works and books for children. His many excellent science books
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Speaker 1: for the public cover subjects in mathematics, physics, astronomy, chemistry,
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Speaker 1: and biology, such as The Genetic Code Inside the Atom,
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Speaker 1: Building Blocks of the Universe, The Living River, The New
1:58
Speaker 1: Intelligent Man's Guide to Science, and Asimov's Biographical Encyclopedia of
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Speaker 1: Science and Technology. In nineteen sixty five, doctor Asimov received
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Speaker 1: the James T. Grady Award of the American Chemical Society
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Speaker 1: for his major contribution in reporting science progress to the public.
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Speaker 1: Theodosius Dubzhansky was graduated from Kiev University and is now
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Speaker 1: a professor at the Rockefeller University. He has done research
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Speaker 1: in genetics and biological evolution on every continent except Antarctica.
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Speaker 1: Among his distinguished published works Radiation Genes in Man, Heredity
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Speaker 1: and the Nature of Man, Mankind Evolving and Evolution Genetics
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Speaker 1: in Man. Mister Dubzhansky received the Daniel G. Elliott price
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Speaker 1: In Medal and the Kimber Genetics Award from the National
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Speaker 1: Academy of Sciences in nineteen fifty eight, and the National
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Speaker 1: Medal of Science awarded by the President of the United
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Speaker 1: States in nineteen sixty five. In the preface and the.
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Speaker 2: Authors section one of the Genetic Effects of radiation. This
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Speaker 2: is a liberovox recording. All liberovox recordings are in the
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Speaker 2: public domain. For more information or to volunteer, please visit
3:16
Speaker 2: LibriVox dot org. Read by Caveat The Genetic Effects of
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Speaker 2: Radiation by Isaac Asimov and Theodosius Dobzansky, The Genetic Effects
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Speaker 2: of Radiation Machinery of inheritance introduction. There is nothing new
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Speaker 2: under the Sun, says the Bible, nor is the Sun
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Speaker 2: itself knew. We might add, as long as life has
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Speaker 2: existed on Earth, it has been exposed to radiation from
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Speaker 2: the Sun, so that life and radiation are old acquaintances
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Speaker 2: and have learned to live together. We are accustomed to
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Speaker 2: looking upon sunlight as something good, useful, and desirable, and
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Speaker 2: certainly we could not long live without it. The energy
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Speaker 2: of sunlight warms the Earth, produces the winds, and tend
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Speaker 2: to equalize Earth's temperatures, rates the oceans, and produces rain
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Speaker 2: and fresh water. Most important of all, it supplies what
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Speaker 2: is needed for green plants to convert carbon dioxide and
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Speaker 2: water into food and oxygen, making it possible for all
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Speaker 2: animal life, including ourselves, to live. Yet sunlight has its
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Speaker 2: dangers too. Lizards avoid the direct rays of the noonday
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Speaker 2: sun on the desert, and we ourselves take precautions against
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Speaker 2: sunburn and sunstroke. The same division into good and bad
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Speaker 2: is to be found in connection with other forms of radiation,
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Speaker 2: forms of which mankind has only recently become aware. Such radiations,
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Speaker 2: produced by radioactivity in the soil and reaches from outer space,
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Speaker 2: have been with us from the beginning of time. They
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Speaker 2: are more energetic than sunlight, however, and can do more damage,
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Speaker 2: and because our senses do not detect them, we have
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Speaker 2: not learned to take precautions against them. To be sure,
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Speaker 2: energetic radiation is present in nature only in very small amounts,
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Speaker 2: and is not therefore much of a danger. Man, however,
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Speaker 2: has the capacity for imitating nature. Long ago in dim prehistory,
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Speaker 2: for instance, he learned to manufacture a kind of sunlight
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Speaker 2: by setting wood and other fuels on fire. This involved
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Speaker 2: a new kind of good and bad our whole. New
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Speaker 2: technology became possible, on the one hand, and on the
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Speaker 2: other the chance of death by burning was also possible.
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Speaker 2: The good in this case far outweighs the evil. In
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Speaker 2: our own twentieth century mankind learned to produce energetic radiation
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Speaker 2: in concentrations far surpassing those we usually encounter in nature. Again,
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Speaker 2: a new technology is resulting, and again there is the
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Speaker 2: possibility of death. The balance in this second instance is
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Speaker 2: less certainly in favor of good over evil. To shift
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Speaker 2: the balance clearly in favor of the good, it is
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Speaker 2: necessary for mankind to learn as much as possible about
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Speaker 2: the new dangers in order that we may minimize them
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Speaker 2: and most effectively guard against them. To see the nature
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Speaker 2: of the danger, let us begin by considering the living
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Speaker 2: tissue itself, the living tissue that must withstand the radiation
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Speaker 2: and that can be damaged by it. End of Section
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Speaker 2: one Section two of the Genetic Effects of radiation. This
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Speaker 2: is a LibriVox recording. All LibriVox recordings are in the
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Speaker 2: public domain. For more information or to volunteer, please visit
6:20
Speaker 2: LibriVox dot org. Read by caveat the Genetic Effects of
6:26
Speaker 2: radiation by Isaac Asimov and Theodosius Dobzantsky. Cells and chromosomes.
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Speaker 2: The average human adult consists of about fifty trillion cells
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Speaker 2: fifty trillion microscopic, more or less self contained blobs of life.
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Speaker 2: He begins life, however, as a single cell, the fertilized ovum.
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Speaker 2: After the fertilized ovum is formed, it divides. It becomes
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Speaker 2: two cells. Each daut cell divides to produce a total
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Speaker 2: of four cells in each of those divides, and so on.
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Speaker 2: There is a high degree of order direction to those divisions.
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Speaker 2: When a human fertilized oven completes divisions, an adult human
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Speaker 2: being is the inevitable result. The fertilized omer of a
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Speaker 2: giraffe will produce a giraffe, That of a fruit fly
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Speaker 2: will produce a fruit fly, and so on. There are
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Speaker 2: no mistakes. It is quite clear that the fertilized oval
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Speaker 2: must carry instructions that guide its development in the appropriate direction.
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Speaker 2: These instructions are contained in the cells chromosomes, tiny structures
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Speaker 2: that appear most clearly like like stubby bits of tangled
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Speaker 2: spaghetti when the cell is in the actual process of division.
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Speaker 2: Each species has some characteristic number of chromosomes in its cells,
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Speaker 2: and these chromosomes can be considered in pairs. Human cells,
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Speaker 2: for instance, contain twenty three pairs of chromosomes forty six
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Speaker 2: in all. When a cell is undergoing division mitosis, the
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Speaker 2: number of chromosomes is temporarily doubled, as each chromosome begins
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Speaker 2: about the formation of a replica of itself. This process
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Speaker 2: is called replication. As the cell devised, the chromosomes are
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Speaker 2: evenly shared by the new cells in such a way
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Speaker 2: that if a particular chromosome goes into one dota cell,
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Speaker 2: its replica goes into the other. In the end, each
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Speaker 2: cells a complete set of pairs of chromosomes, and the
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Speaker 2: set in each cell is identical with the set in
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Speaker 2: the original cell before division. To study chromosomes, scientists begin
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Speaker 2: with the cell that is in the process dividing. When
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Speaker 2: chromosomes are in their most visible form. Then they treat
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Speaker 2: the cell with a chemical a derivative calcachen to arrest
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Speaker 2: a cell division at a metavase stage. This brings about
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Speaker 2: a result like the photomicrograph above. Chromosomes are visible but
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Speaker 2: still too tangled to be counted or measured. Then the
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Speaker 2: cell is treated with a low concentration salt solution, which
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Speaker 2: swells the chromosomes and dispersism so they become distinct structures
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Speaker 2: as below. The separate chromosomes in a dividing cell of
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Speaker 2: photographed and then can be identified by their overall length,
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Speaker 2: the position of the centromere, or point where the two
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Speaker 2: strands join in other characteristics. Photo micrograph can then be
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Speaker 2: cut apart and the chromosomes grouped in a karatype, which
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Speaker 2: is an arrangement according to a standard classification to show
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Speaker 2: chromosome complement and abnormalities. This charotype below is of a
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Speaker 2: normal male since it shows X and Y sex chromosomes
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Speaker 2: and twenty two pairs of other autosomonal chromosomes. By contrast,
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Speaker 2: for cells in the upper pictures are abnormal with only
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Speaker 2: forty five chromosomes each. In this way, the fundamental instructions
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Speaker 2: that determine the characteristics of a cell are passed on
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Speaker 2: to each new cell. Ideally, all the trillions of cells
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Speaker 2: in a particularly human being have identical sets of instructions.
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Speaker 2: End of section two Section three of the Genetic Effects
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Speaker 2: of radiation. This is a LibriVox recording. All LibriVox recordings
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Speaker 2: are in the public domain. For more information or to volunteer,
9:53
Speaker 2: please visit LibriVox dot org. Read by Caveat The Genetic
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Speaker 2: Effects of Radiation by Isaac Asimov and Theodosius Dovzanski. Enzymes
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Speaker 2: and genes. Each cell is a tiny chemical factory in
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Speaker 2: which several thousand kinds of chemical changes are constantly taking
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Speaker 2: place among the numerous sorts of molecules move about in
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Speaker 2: its fluid that are pinned to its solid structures. These
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Speaker 2: chemical changes are guided and controlled by the existence of
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Speaker 2: as many as thousands of different enzymes within the cell.
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Speaker 2: Enzymes possess large molecules built up of some twenty different
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Speaker 2: but chemically related units called amino acids. Particular enzyme molecule
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Speaker 2: may contain a single amino acid of one type, five
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Speaker 2: of another, several dozen of still another, and so on.
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Speaker 2: All the units are strung together in some specific pattern,
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Speaker 2: in one long chain or in small numbers of close
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Speaker 2: to connected chains. Every different pattern of amino acids forms
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Speaker 2: a molecule with its own set of properties, and there
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Speaker 2: are an enormous number of patterns possible. In an enzyme
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Speaker 2: molecule made up of five hundred amino acids, the possible
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Speaker 2: number of patterns can be expressed by one followed by
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Speaker 2: eleven hundred zeros tend to the power of eleven hundred.
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Speaker 2: Each cell has the capacity of choosing among this unimaginable
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Speaker 2: number of possible patterns and selecting those characteristics of itself.
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Speaker 2: It therefore ends with a complement of specific enzymes that
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Speaker 2: guide its own chemical changes and consequently its properties and
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Speaker 2: its behavior. The instructions that enable the fertilized open to
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Speaker 2: develop in a proper manner are essentially instructions for choosing
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Speaker 2: a particular set of enzyme patterns out of all those possible.
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Speaker 2: The differences in the enzyme guided behavior of the cells
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Speaker 2: making up different species show themselves in differences in body structure.
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Speaker 2: We cannot completely follow the long, intricate chain of cause
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Speaker 2: and effect that leads from one set of enzymes to
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Speaker 2: the long neck of a giraffe, and from another set
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Speaker 2: of enzymes to a large brain of a man, but
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Speaker 2: we are sure that the chain is there. Even within
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Speaker 2: a species, different individuals will have slight distinctions among their
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Speaker 2: sets of enzymes, and this accounts for the fact that
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Speaker 2: no two human beings are are exactly alike, leaving identical
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Speaker 2: twins out of consideration. Each chromosome can be considered as
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Speaker 2: being composed of small sections called genes, usually pictures as
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Speaker 2: being strung along the length of the chromosome. Each gene
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Speaker 2: is considered to be responsible for the formation of a
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Speaker 2: chain of amino acids in a fixed pattern. The formation
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Speaker 2: is guided by the details of the gene's own structure,
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Speaker 2: which are the instructions earlier referred to. This gene structure,
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Speaker 2: which can be translated into an enzyme structure, is now
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Speaker 2: called the genetic code. If a particular enzyme or group
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Speaker 2: of enzymes is for any reason formed imperfectly or not
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Speaker 2: at all, this may show up as some visible abnormality
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Speaker 2: of the body and inability to see colour, for instance,
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Speaker 2: or the possession of two joints to each finger rather
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Speaker 2: than three. It is much easier to observe physical differences
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Speaker 2: than some delicate chains in the enzyme pattern of the cells.
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Speaker 2: Genes are therefore usually referred to by the body chains
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Speaker 2: that they bring about, and one can, for instance, speak
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Speaker 2: of a gene for colourblind. A gene may exist in
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Speaker 2: two or more varieties, each producing a slightly different enzyme,
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Speaker 2: a situation that is reflected in turning slight changes in
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Speaker 2: body characteristics. Thus, there are genes governing eye color, one
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Speaker 2: of which is sufficiently important to be considered a gene
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Speaker 2: for blue eyes, and another gene for brown eyes. One
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Speaker 2: or the other, but not both, we found a specific
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Speaker 2: place on a specific chromosome. The two chromosomes of a
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Speaker 2: particular pair govern identical sets of characteristics. Both, for instance,
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Speaker 2: will have a place for genes governing eye colour if
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Speaker 2: we consider only the most important varieties involved. Those on
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Speaker 2: each chromosome of the pair may be identical both, maybe
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Speaker 2: for the blue eyes, or both maybe for brown eyes.
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Speaker 2: In that case, the individual is homozygous for that characteristic
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Speaker 2: and may be referred to as a homozygote. The chromosomes
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Speaker 2: of the pair may carry different varieties a gene for
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Speaker 2: blue eyes on one chromosome and one for brown eyes
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Speaker 2: on the other. The individual is then heterozygous for that
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Speaker 2: characteristic and referred to as heterozygote. Naturally, particular individuals may
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Speaker 2: be homozygous for some types of characteristics and heterozygous for others.
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Speaker 2: When an individual is heterozygous for a particular characteristic, it
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Speaker 2: frequently happens that he shows the effect associated with one
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Speaker 2: of the gene varieties. If he possesses both a gene
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Speaker 2: for brown eyes and one for blue eyes, his eyes
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Speaker 2: are just as brown as though he had carried two
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Speaker 2: genes for brown eyes. The gene for brown eyes is
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Speaker 2: dominant in this case, while the gene for blue eyes
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Speaker 2: is recessive. End of section three.
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Speaker 3: Section four of the Genetic Effects of Radiation. This is
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Speaker 3: a LibriVox recording. All LibriVox recordings are in the public domain.
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Speaker 3: For more information or to volunteer, please visit LibriVox dot org.
14:55
Speaker 3: The Genetic Effects of Radiation by Isaac Asimo and Theodosius
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Speaker 3: Dobzansky Parents and offspring. How does the fertilized ovum obtain
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Speaker 3: its particular set of chromosomes? In the first place, each
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Speaker 3: adult possesses gonads, in which sex cells are formed in
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Speaker 3: the male. Sperm cells are formed in the testes in
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Speaker 3: the female. Egg cells are formed in the ovaries. In
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Speaker 3: the formation of the sperm cells and egg cells, there
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Speaker 3: is a key step myosis, a cell division, in which
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Speaker 3: the chromosomes group into pairs and are then apportioned between
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Speaker 3: the daughter cells, one of each pair to each cell.
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Speaker 3: Such a division, unaccompanied by replication, means that in place
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Speaker 3: of the usual twenty three pairs of chromosomes in each cell,
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Speaker 3: each sex cell has twenty three individual chromosomes, a half set,
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Speaker 3: so to speak. In the process of fertilization, a sperm
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Speaker 3: cell from the father enters and merges with an egg
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Speaker 3: cell from the mother. The fertilized ovum that results now
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Speaker 3: has a full set of twenty three pairs of chromosomes,
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Speaker 3: but of each pair, one comes from the father and
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Speaker 3: one from the mother. In this way, each newborn child
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Speaker 3: is a true individual, with its characteristics based on a
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Speaker 3: random reshuffling of chromosomes in forming the sex cells. The
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Speaker 3: chromosome pairs can separate in either fashion A into cell
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Speaker 3: one and B into cell two, or vice versa. If
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Speaker 3: each of twenty three pairs does this randomly, nearly ten
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Speaker 3: million different combinations of chromosomes are possible in the sex
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Speaker 3: cells of a single individual. Furthermore, one can't predict which
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Speaker 3: chromosome combination in the sperm cell will end up in
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Speaker 3: combination with which in the egg cell, so that by
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Speaker 3: this reasoning, a single married couple could produce children with
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Speaker 3: any of one hundred trillion possible chromosome combinations. It is
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Speaker 3: this that begins to explain the endless variety among living beings.
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Speaker 3: Even within a particular species, It only begins to explain
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Speaker 3: it because there are other sources of difference.
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Speaker 4: Two.
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Speaker 3: A chromosome is capable of exchanging pieces with its pair,
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Speaker 3: producing chromosomes with a brand new pattern of gene varieties.
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Speaker 3: Before such a crossover, one chromosome may have carried a
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Speaker 3: gene for blue eyes and one for wavy hair, while
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Speaker 3: the other chromosome may have carried a gene for brown
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Speaker 3: eyes and one for straight hair. After the crossover, one
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Speaker 3: would carry genes for blue eyes and straight hair, the
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Speaker 3: other for brown eyes and wavy hair. End of section
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Speaker 3: four read by Carrie Adams your book Voice at Mesa,
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Speaker 3: Arizona on the twenty fourth of March twenty twenty two.
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Speaker 5: Section five of the Genetic Effects of radiation. This is
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Speaker 5: a LibriVox recording. All LibriVox recordings are in the public domain.
18:49
Speaker 5: For more information or volunteer, please visit LibriVox dot org.
18:54
Speaker 5: The Genetic Effects of Radiation by Isaac Asimov and Theodosius Dobzanski.
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Speaker 5: Mutations sudden change shifts in chromosome combinations with or without crossovers,
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Speaker 5: can produce unique organisms with characteristics not quite like any
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Speaker 5: organism that appeared in the past, nor likely to appear
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Speaker 5: in the reasonable future. They may even produce novelties in
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Speaker 5: individual characteristics. Since genes can affect one another, and a
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Speaker 5: gene surrounded by unusual neighbors can produce unexpected effects, Matters
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Speaker 5: can go further still. However, in the direction of novelty,
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Speaker 5: it is possible for chromosomes to undergo more serious changes,
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Speaker 5: either structural or chemical, so that entirely new characteristics are
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Speaker 5: produced that might not otherwise exist. Such changes are called mutations.
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Speaker 5: We must be careful how we use this term. A
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Speaker 5: child may possess some characteristics not present in either parent
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Speaker 5: through the mere shuffling of chromosomes, and not through mutation. Suppose,
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Speaker 5: for instance, that a man is heterozygous to eye color,
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Speaker 5: carrying one gene for brown eyes and one for blue eyes.
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Speaker 5: His eyes would of course be brown, since the gene
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Speaker 5: for brown eyes is dominant over that for blue Half
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Speaker 5: the sperm cells he produces would carry a single gene
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Speaker 5: for brown eyes in its half set of chromosomes. The
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Speaker 5: other half would carry a single gene for blue eyes.
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Speaker 5: If his wife were similarly heterozygous and therefore also had
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Speaker 5: brown eyes. Half her egg cells would carry the gene
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Speaker 5: for brown eyes and half the gene for blue It
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Speaker 5: might follow in this marriage, then, that a sperm carrying
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Speaker 5: the gene for blue eyes might fertilize an egg carrying
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Speaker 5: the gene for blue eyes. The child would then be
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Speaker 5: homozygous with two genes for blue eyes, and he would
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Speaker 5: definitely be blue eyed. In this way, two brown eyed
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Speaker 5: parents might have a blue eyed child, and this would
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Speaker 5: not be a mutation. If the parent's ancestry were traced
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Speaker 5: further back, blue eyed individuals would undoubtedly be found on
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Speaker 5: both sides of the family tree. If, however, there were
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Speaker 5: no record of, say anything but normal color vision in
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Speaker 5: a child's ancestry, and he were born color blind, that
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Speaker 5: could be assumed to be the result of a mutation.
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Speaker 5: Such a mutation could then be passed on by the
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Speaker 5: normal modes of inheritance, and a certain proportion of the
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Speaker 5: child's eventual descendants would be color blind. A mutation may
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Speaker 5: be associated with changes in chromosome structure sufficiently drastic to
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Speaker 5: be visible under the microscope. Such chromosome mutations can arise
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Speaker 5: in several ways, chromosomes may undergo replication without the cell
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Speaker 5: itself dividing. In that way, cells can develop with two, three,
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Speaker 5: or four times the normal complement of chromosomes, and organisms
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Speaker 5: made up of cells displaying such polyploidy can be markedly
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Speaker 5: different from the norm. This situation is found chiefly among
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Speaker 5: plants and among some groups of invertebrates. It does not
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Speaker 5: usually occur in mammals, and when it does, it leads
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Speaker 5: to quick death. Less extreme changes take place two as
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Speaker 5: when a particular chromosome breaks and fails to reunite, or
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Speaker 5: when several break and then reuniting correctly. Under such conditions,
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Speaker 5: the mechanism by which chromosomes are distributed among the daughter
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Speaker 5: cells is not likely to work correctly. Sex Cells may
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Speaker 5: then be produced with a piece of chromosome or a
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Speaker 5: whole one missing, or with an extra piece or whole
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Speaker 5: chromosome present. In nineteen fifty nine, such a situation was
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Speaker 5: found to exist in the case of persons suffering from
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Speaker 5: a long known disease called down syndrome. Each person so
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Speaker 5: affected has forty seven chromosomes in place of the normal
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Speaker 5: forty six. It turned out that the twenty first pair
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Speaker 5: of chromosomes using a convention whereby the chromosome pairs are
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Speaker 5: numbered in order of decreasing size, consists of three individuals
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Speaker 5: rather than two. The existence of this chromosome abnormality clearly
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Speaker 5: demonstrated what had previously been strongly suspected that down syndrome
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Speaker 5: originates as a mutation and is inborn. Most mutations, however,
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Speaker 5: are not associated with any noticeable change in chromosome structure.
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Speaker 5: There are instead, more subtle changes in the chemical structure
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Speaker 5: of the genes that make up the chromosome. Then we
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Speaker 5: have gene mutations. The process by which a gene produces
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Speaker 5: its own replica is complicated, and while it rarely goes wrong,
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Speaker 5: it does misfire on occasion. Then two, even when a
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Speaker 5: gene molecule is replicated perfectly, it may undergo change afterward
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Speaker 5: through the action upon it of some chemical or other
23:46
Speaker 5: environmental influence. In either case, a new variety of particular
23:51
Speaker 5: gene is produced, and if present in a sex cell,
23:55
Speaker 5: it may be passed on to descendants through an indefinite
23:58
Speaker 5: number of generations. Of course, chromosome or gene mutations may
24:03
Speaker 5: take place in ordinary cells rather than in sex cells.
24:07
Speaker 5: Such changes in ordinary cells are somatic mutations. When mutated
24:12
Speaker 5: body cells divide, new cells with changed characteristics are produced.
24:17
Speaker 5: These changes may be trivial, or they may be serious.
24:21
Speaker 5: It is often suggested, for instance, that cancer may result
24:25
Speaker 5: from a somatic mutation in which certain cells lose the
24:28
Speaker 5: capacity to regulate their growth properly. Since somatic mutations do
24:33
Speaker 5: not involve the sex cells, they are confined to the
24:36
Speaker 5: individual and are not passed on to the offspring. End
24:40
Speaker 5: of section five section six of the Genetic Effects of Radiation.
24:50
Speaker 5: This is a LibriVox recording. All LibriVox recordings are in
24:53
Speaker 5: the public domain. For more information or to volunteer, please
24:57
Speaker 5: visit LibriVox dot org. The Gene Meetic Effects of Radiation
25:01
Speaker 5: by Isaac Asimov and Theodosius Dubzonski. Spontaneous mutations mutations that
25:08
Speaker 5: take place in the ordinary course of nature without man's
25:11
Speaker 5: interference are spontaneous mutations. Most of these arise out of
25:16
Speaker 5: the very nature of the complicated mechanism of gene replication.
25:21
Speaker 5: Copies of genes are formed out of a large number
25:24
Speaker 5: of small units that must be lined up in just
25:26
Speaker 5: the right pattern to form one particular gene in no
25:29
Speaker 5: other ideally matters are so arranged within the cell that
25:34
Speaker 5: the necessary changes giving rise to the desired pattern are
25:38
Speaker 5: just those that have a maximum probability. Other changes are
25:42
Speaker 5: less likely to happen, but are not absolutely excluded. Sometimes,
25:47
Speaker 5: through the accidental jostling of molecules, a wrong turn may
25:51
Speaker 5: be taken, and the result is a spontaneous mutation. We
25:55
Speaker 5: might consider a mutation to be either good or bad,
25:59
Speaker 5: in the sense that an any change that helps a
26:01
Speaker 5: creature live more easily and comfortably is good, and that
26:04
Speaker 5: the reverse is bad. It seems reasonable that random changes
26:09
Speaker 5: in the gene pattern are almost sure to be bad.
26:12
Speaker 5: Consider that any creature, including man, is the product of
26:16
Speaker 5: millions of years of evolution. In every generation, those individuals
26:21
Speaker 5: with a gene pattern that fit them better for their
26:24
Speaker 5: environment when out over those with less effective patterns. When
26:28
Speaker 5: out in the race for food, for mates, and for safety,
26:32
Speaker 5: the more fit had more offspring and crowded out the
26:35
Speaker 5: less fit. By now, then, the set of genes with
26:38
Speaker 5: which we are normally equipped is the end product of
26:41
Speaker 5: long ages of such natural selection. A random change cannot
26:46
Speaker 5: be expected to improve it any more than random changes
26:50
Speaker 5: would improve any very complex, intricate, and delicate structure. Yet
26:55
Speaker 5: over the eons, creatures have in d changed largely through
26:59
Speaker 5: the effect mutation. If mutations are almost always for the worse,
27:04
Speaker 5: how can one explain that evolution seems to progress toward
27:08
Speaker 5: the better, and that out of a primitive form as
27:10
Speaker 5: simple as an omiba, for instance, their eventually emerged man
27:15
Speaker 5: In the first place. Environment is not fixed. Climate changes,
27:20
Speaker 5: conditions change the food supply, may change the nature of living.
27:24
Speaker 5: Enemies may change. A gene pattern that is very useful
27:28
Speaker 5: under one set of conditions may be less useful under another. Suppose,
27:32
Speaker 5: for instance, that man had lived in tropical areas for
27:36
Speaker 5: thousands of years and had developed a heavily pigmented skin
27:39
Speaker 5: as a protection against sunburn. Any child who, through a mutation,
27:44
Speaker 5: found himself incapable of forming such pigment would be at
27:48
Speaker 5: a severe disadvantage. In the outdoor activities engaged in by
27:52
Speaker 5: his tribe, he would not do well, and such a
27:55
Speaker 5: mutated gene would never establish itself for long. If a
27:59
Speaker 5: number of these these men migrated to northern Europe, however,
28:02
Speaker 5: children with dark skin would absorb insufficient sunlight during the
28:07
Speaker 5: long winter, when the sun was low in the sky
28:09
Speaker 5: and visible for brief periods. Only dark skinned children would,
28:14
Speaker 5: under such conditions tend to suffer from rickets. Mutant children
28:18
Speaker 5: with pale skin would absorb more of what weak sunlight
28:22
Speaker 5: there was and would suffer less. There would be little
28:25
Speaker 5: danger of sunburn, so there would be no penalty counteracting
28:29
Speaker 5: this new advantage of pale skins. It would be the
28:32
Speaker 5: dark skinned people who would tend to die out. In
28:36
Speaker 5: the end, you would have dark skins in Africa and
28:39
Speaker 5: pale skins in Scandinavia, and both would be fit in
28:44
Speaker 5: the same way. Any child born into a primitive hunting
28:47
Speaker 5: society who found himself with a mutated gene that brought
28:51
Speaker 5: about near sightedness would be at a distinct disadvantage. In
28:55
Speaker 5: a modern technological society. However, near sighted individual doing more
29:01
Speaker 5: poorly at outdoor games are often driven into quieter activities
29:05
Speaker 5: that involve reading, thinking, and studying. This may lead to
29:09
Speaker 5: a career as a scientist, scholar, or professional man, categories
29:14
Speaker 5: that are valuable in such a society and are encouraged.
29:18
Speaker 5: Near Sightedness would therefore spread more generally through civilized societies
29:22
Speaker 5: than through primitive ones. Then, too, a gene may be
29:26
Speaker 5: advantageous when it occurs in low numbers, and disadvantageous when
29:30
Speaker 5: it occurs in high numbers. Suppose there was a gene
29:34
Speaker 5: among humans that so affected the personality as to make
29:37
Speaker 5: it difficult for a human being to endure crowded conditions.
29:42
Speaker 5: Such individuals would make good explorers, farmers, and herdsmen, but
29:46
Speaker 5: poor city dwellers. Even in our modern urbanized society. Such
29:51
Speaker 5: a gene in moderate concentration would be good, since we
29:55
Speaker 5: still need our outdoorsmen. In high concentration, it would be bad.
30:00
Speaker 5: For then the existence of areas of high population density,
30:04
Speaker 5: on which our society now seems to depend might become impossible.
30:09
Speaker 5: In any species, then, each gene exists in a number
30:12
Speaker 5: of varieties upon which an absolute good or bad cannot
30:17
Speaker 5: be unequivocally stamped. These varieties make up the gene pool,
30:22
Speaker 5: and it is this gene pool that makes evolution possible.
30:26
Speaker 5: A species with an invariable set of genes could not
30:30
Speaker 5: change to suit altered conditions. Even a slight shift in
30:34
Speaker 5: the nature of the environment might suffice to wipe it out.
30:38
Speaker 5: The possession of a gene pool ends flexibility. However, as
30:42
Speaker 5: conditions change, one combination of varieties might gain over another,
30:47
Speaker 5: and this in turn, might produce changes in body characteristics
30:51
Speaker 5: that would then further alter the relative goodness or badness
30:55
Speaker 5: of certain gene patterns. Thus, over the past million years,
30:59
Speaker 5: for example, the human brain has, through mutations and appropriate
31:04
Speaker 5: shifts in emphasis within the gene pool, increased notably in size.
31:10
Speaker 5: End of section six.
31:17
Speaker 4: Section seven of the Genetic Effects of Radiation. This is
31:21
Speaker 4: a LibriVox recording. All LibriVox recordings are in the public domain.
31:25
Speaker 4: For more information or to volunteer, please visit LibriVox dot org.
31:30
Speaker 4: Read by Ethan Montese, The Genetic Effects of Radiation, my
31:35
Speaker 4: Isaac Asimov and Theodosius Dobzinsky Genetic load. Some gene mutations
31:42
Speaker 4: produce characteristics so undesirable that it is difficult to imagine
31:46
Speaker 4: any reasonable change in environmental condition that make them beneficial.
31:50
Speaker 4: There are mutations that lead to the non development of
31:52
Speaker 4: hands and feet, to the production of blood that will
31:55
Speaker 4: not clot, to serious malformations of essential organs, and so on.
32:00
Speaker 4: Such mutations are unqualifiedly bad. The badness may be so
32:04
Speaker 4: severe that a fertilized ovum may be incapable of development,
32:07
Speaker 4: or if it develops, the fetus miscarries, or the child
32:10
Speaker 4: is stillborn, or if the child is born alive, it
32:13
Speaker 4: dies before mature, so that it can never have children
32:15
Speaker 4: of its own. Any mutation that brings about death before
32:17
Speaker 4: the gene producing it can be passed on to another
32:19
Speaker 4: generation is a lethal mutation. A gene governing a lethal
32:24
Speaker 4: characteristic may be dominant, will then kill, even though the
32:27
Speaker 4: corresponding gene on the other chromosome or the pair is normal.
32:30
Speaker 4: Under such conditions, the lethal gene is removed in the
32:32
Speaker 4: same generation in which it is formed. The lethal gene may,
32:35
Speaker 4: on the other hand, be recessive, Its effect is then
32:37
Speaker 4: not evident. If the gene is paired with its normal
32:39
Speaker 4: the normal gene carries on for both. When this is
32:42
Speaker 4: the case, the lethal general men in existence and will
32:45
Speaker 4: every once in a while make itself evident if two
32:47
Speaker 4: people each serving as a carrier with such a gene
32:50
Speaker 4: have children. A sperm cell carrying a lethal may fertilize
32:53
Speaker 4: an egg carrying the same type of lethal, with sad results.
32:56
Speaker 4: Every species, including man, includes the individuals who carry on
33:00
Speaker 4: desirable genes. These undesirable genes we passed along for generations,
33:04
Speaker 4: even if dominant before natural selection culps them ount the
33:07
Speaker 4: more seriously undesirable they are, the more quickly they are removed,
33:10
Speaker 4: but even outright lethal genes will be included among the
33:13
Speaker 4: chromosomes from generation to generation, provided they are recessive. These
33:17
Speaker 4: deleterious genes make up the genetic load. The only way
33:21
Speaker 4: to avoid a genetic load is to have no mutations
33:23
Speaker 4: and therefore no gene pool. The gene pool is necessary
33:26
Speaker 4: for the flexibility that will allow species to survive and
33:29
Speaker 4: evolve over the eons, and the genetic load is the
33:31
Speaker 4: price that must be paid for that. Generally, the capacity
33:34
Speaker 4: for a species to reproduce itself is sufficiently high to
33:37
Speaker 4: make up quite easily the numbers launched the combination of
33:40
Speaker 4: deleterious genes. The size of genetic load depends on two factors,
33:44
Speaker 4: the rate of which deleterious gene is produced through mutation
33:47
Speaker 4: and the rate of which it is moved by natural selection.
33:49
Speaker 4: When the rate of removal equals the rate of production,
33:52
Speaker 4: a condition of genetic equilibrium is reached, and the level
33:54
Speaker 4: of occurrence of that gene then remains stable over the generations,
33:58
Speaker 4: even though deleterious gene are removed relatively rapidly. If dominant
34:02
Speaker 4: and lethal genes are removed, in the same generation at
34:04
Speaker 4: which they are formed. A new crop of deleterious genes
34:07
Speaker 4: will appear by mutation with every succeeding generation. The equilibrium
34:10
Speaker 4: level for such a dominant deleterious gene is relatively low. However,
34:14
Speaker 4: deleterious genes that are assessive are removed much more slowly
34:17
Speaker 4: those persons. The two such genes who alone show the
34:19
Speaker 4: bad effects are that the visible portion of iceberg, and
34:22
Speaker 4: represent only a small part of the whole. The heterozygotes
34:25
Speaker 4: or carriers who possess a single gene of the sort
34:28
Speaker 4: and who live out normal lives keep that gene in being.
34:31
Speaker 4: If people in a particular population marry randomly, and if
34:34
Speaker 4: one of a million is born homozygous for a certain
34:37
Speaker 4: deleterious recessive gene and dies of it, one out of
34:40
Speaker 4: five hundred is heterozygous for that same gene, shows no
34:44
Speaker 4: ill effect, and as the capable of passing it on.
34:46
Speaker 4: It may be that the heterozygote is not quite normal,
34:48
Speaker 4: but does show some ill effects, not enough to incommode
34:51
Speaker 4: him seriously, perhaps, but enough to lower his chance is
34:54
Speaker 4: slightly for mating and bearing children. In that case, the
34:56
Speaker 4: equilibrium level for that gene will be lower than otherwise
34:59
Speaker 4: would be. It may also be that the heterozygote experiences
35:02
Speaker 4: an actual advantage over a normal individual under some conditions.
35:06
Speaker 4: There is a recessive gene, for instance, that produces a
35:08
Speaker 4: serious disease called sickle cell anemia. People possessing two such
35:12
Speaker 4: genes usually die young. A heterozygot possessing only one of
35:15
Speaker 4: these genes are not seriously affected and has red blood
35:18
Speaker 4: cells that are apparently less appetizing to malaria parasites. The
35:23
Speaker 4: heterozygote therefore experiences a positive advantage if he lives in
35:26
Speaker 4: a region where the incidents of a certain kind of
35:28
Speaker 4: malaria is high. The equilibrium level of the sickle celenemia
35:31
Speaker 4: gene can, in other words, be higher in malaria regions
35:34
Speaker 4: than elsewhere. Here is one subject area on which additional
35:37
Speaker 4: research is urgently needed. And maybe that the usefulness of
35:40
Speaker 4: a single delitarious gene is great that we may suspect
35:42
Speaker 4: in many cases, and that there are greater advantages to
35:45
Speaker 4: heterozygosinths than we know. This may be the basis what
35:48
Speaker 4: is sometimes called hybrid vigor and a world of which
35:51
Speaker 4: human beings are more mobile than they ever have been
35:53
Speaker 4: in history, and in which intercultural marriages are increasingly common.
35:58
Speaker 4: Information on this point is particularly important. End of section seven.
36:07
Speaker 2: Section eight of the Genetic Effects of Radiation. This is
36:11
Speaker 2: a LibriVox recording. All LibriVox recordings are in the public domain.
36:15
Speaker 2: For more information or to volunteer, please visit LibriVox dot org.
36:20
Speaker 2: Read by Caveat The Genetic Effects of Radiation by Isaac
36:24
Speaker 2: Asimov and Theodosius Dobzansky. Mutation rates. It is easier to
36:32
Speaker 2: observe the removal of genes through death or through failure
36:35
Speaker 2: to reproduce than to observe their production through mutation. It
36:39
Speaker 2: is particularly difficult to study their production in human beings,
36:43
Speaker 2: since men have comparatively long lifetimes and few children, since
36:47
Speaker 2: their mating habits cannot be well controlled. For this reason,
36:52
Speaker 2: geneticists have experimented with species much simpler than man. Small
36:56
Speaker 2: organisms that are short lived, produce many offspring, and that
37:00
Speaker 2: can be penned up and allowed to mate only under
37:02
Speaker 2: fixed conditions. Such creatures may have fewer chromosomes than man does,
37:07
Speaker 2: and the sites of mutation are more easily pinned down.
37:11
Speaker 2: An important assumption made in such experiments is that the
37:14
Speaker 2: machinery of inheritance and mutation is essentially the same in
37:18
Speaker 2: all creatures, and that therefore knowledge gained from very simple species,
37:22
Speaker 2: even from bacteria, is applicable to man. There is overwhelming
37:27
Speaker 2: evidence to indicate that this is true in general, although
37:30
Speaker 2: there are specific instances where it is not completely true,
37:33
Speaker 2: and scientists must tread softly while drawing conclusions. The animals
37:38
Speaker 2: most commonly used in studies of genetics and mutations are
37:42
Speaker 2: certain species of fruit flies called Josophala. The American geneticist
37:46
Speaker 2: Hermann J. Muller devised techniques whereby he could study the
37:50
Speaker 2: occurrence of lethal mutations anywhere along one of four pairs
37:54
Speaker 2: of chromosomes possessed by Gisophala. A lethal gene, he found,
37:59
Speaker 2: might well be produced somewhere along the length of a
38:01
Speaker 2: particular chromosome once out of every two hundred times that
38:04
Speaker 2: chromosome underwent replication. This means that out of every two
38:09
Speaker 2: hundred sex cells produced by Gsophla, one would contain a
38:13
Speaker 2: lethal gene somewhere along the length of that chromosome. That
38:18
Speaker 2: particular chromosome, however, contained at least five hundred genes capable
38:22
Speaker 2: of undergoing a lethal mutation. If each of those genes
38:25
Speaker 2: is equally likely to undergo such a mutation. Then the
38:28
Speaker 2: chance that any one particular gene is lethal is one
38:31
Speaker 2: out of two hundred times five hundred, or one out
38:34
Speaker 2: of every hundred thousand. This is a typical mutation rate
38:38
Speaker 2: for a gene in higher organisms, generally, as far as
38:41
Speaker 2: geneticists can tell, though the rates are lower among bacteria
38:45
Speaker 2: and viruses. Naturally, a chaz Per mutation takes place every
38:50
Speaker 2: time a new individual is born. Fruit Flies have many
38:53
Speaker 2: more offspring per year than human beings, since their generations
38:57
Speaker 2: are shorter and they produce more young at a time.
39:00
Speaker 2: For that reason, though the mutation rate may be the
39:03
Speaker 2: same in fruit flies as in man, many more actual
39:06
Speaker 2: mutations are produced per unit time in fruit flies than
39:09
Speaker 2: in men. This does not mean that the situation may
39:13
Speaker 2: be ignored in the case of man. Suppose the rate
39:16
Speaker 2: of production of a particular deletarious gene in man is
39:19
Speaker 2: one out of a hundred thousand. It is estimated that
39:22
Speaker 2: a human being has at least ten thousand different genes,
39:26
Speaker 2: and therefore the chance that at least one of the
39:28
Speaker 2: genes is a sex cell is deleterious is ten thousand
39:31
Speaker 2: out of a hundred thousand or one out of ten. Furthermore,
39:36
Speaker 2: it is estimated that the number of gene mutations that
39:38
Speaker 2: are weakly deletarious are four times as numerous as though
39:42
Speaker 2: that are strongly deliterious or lethal. The chances at least
39:46
Speaker 2: one gene in a sex cell is at least weekly
39:48
Speaker 2: deleterious then would be four plus one out of ten
39:52
Speaker 2: or one out of two. Naturally, these deliterious genes are
39:56
Speaker 2: not necessarily spread out evenly among human beings. With one
40:00
Speaker 2: to a sex cell, some sex cells would be carrying
40:02
Speaker 2: more than one, thus increasing the number that may be
40:05
Speaker 2: expected to carry none at all. Even so, it is
40:08
Speaker 2: supposed that very nearly half the sex cells produced by
40:11
Speaker 2: humanity carry at least one deliarious gene. Even though only
40:17
Speaker 2: half the sex cells are free of deliarious genes, it
40:20
Speaker 2: is still possible to produce a satisfactory new generation of men.
40:24
Speaker 2: Yet one can see that the genetic load is quite
40:26
Speaker 2: heavy that anything that would tend to increase it would
40:29
Speaker 2: certainly be undesirable and perhaps even dangerous. We tend to
40:34
Speaker 2: increase the genetic load by reducing the rate at which
40:36
Speaker 2: deliterarious genes are removed, that is, by taking care of
40:40
Speaker 2: the sick and retarded, and by trying to prevent discomfort
40:43
Speaker 2: and death at all levels. There is, however, no humane
40:47
Speaker 2: alternative to this. What's more, it is by and large
40:51
Speaker 2: only those with slightly deliterious genes who are preserved genetically.
40:55
Speaker 2: It is those persons with near sightedness, with diabetes and
40:59
Speaker 2: so on, who, with the aid of glasses, intulne or
41:02
Speaker 2: other props, can go on to live normal lives and
41:05
Speaker 2: have children in the usual numbers. Those with strongly deliterious
41:08
Speaker 2: genes either die despite all that can be done for
41:11
Speaker 2: them even to day, or at least do not have
41:13
Speaker 2: a chance to have as many children. The danger of
41:17
Speaker 2: an increase in the genetic load rests more heavily than
41:19
Speaker 2: at the other end a measures that usually inadversibly or
41:23
Speaker 2: intentionally increase the rate of production of mutant genes. It
41:27
Speaker 2: is to this matter we will now turn end of
41:31
Speaker 2: section eight.
41:38
Speaker 6: Section nine of the Genetic A fix of radiation. This
41:42
Speaker 6: is a libertywox recording. All liberywalkx recordings are in the
41:46
Speaker 6: public domain. For more information or to volunteer, please visit
41:51
Speaker 6: liberywalkx dot org. Read by Jorganan genetic fix of radiation
41:56
Speaker 6: by Isaac Asimov and Theodosius Dobzansky radiation ionizing radiation. A
42:06
Speaker 6: modern technological civilization exposes mankind to two general types of
42:10
Speaker 6: genetic dangers unknown earlier synthetic chemicals or unprecedentedly high concentrations
42:17
Speaker 6: of natural ones absent in earlier eras, and intensities of
42:21
Speaker 6: energetic variation. Equally unknown or unprecedented chemicals can interfere with
42:27
Speaker 6: the process of replication by offering alternate pathways with which
42:30
Speaker 6: the cellular machionary is not prepared to cope. In general, however,
42:34
Speaker 6: it is only those cells in direct contact with chemicals
42:37
Speaker 6: that are so affected, such as the skin, the intertinal linings,
42:41
Speaker 6: the lungs, and the liver, which is active in altering
42:44
Speaker 6: and getting rid of foreign chemicals. These may undergo somatic mutations,
42:49
Speaker 6: and an increased incidence of cancer in those tissues is
42:52
Speaker 6: among the drastic results of exposure to certain chemicals. Such
42:56
Speaker 6: chemicals are, not, however, likely to come in contact with
42:58
Speaker 6: the gonads where the sex is are produced. While individual
43:02
Speaker 6: persons may be threatened by the manner in which the
43:04
Speaker 6: environment is being permeated with novel chemicals, the next generation
43:07
Speaker 6: is not affected in advance Radiation is another matter in
43:11
Speaker 6: its broadest sense, variations any phenomena spreading out from some
43:15
Speaker 6: sorts in all directions. Physically, such radiation may consist of
43:20
Speaker 6: waves or of particles. Footnote. Actually, all waves have some
43:25
Speaker 6: of the characteristics of particles, and all particles have some
43:29
Speaker 6: of the characteristics of waves. Usually, however, the radiation is
43:32
Speaker 6: predominantly one or the other, and little confusion arises under
43:36
Speaker 6: the ordinary circumstances in speaking of waves and particles as
43:40
Speaker 6: though they were separate phenomena. End of footnote. Of the
43:44
Speaker 6: wave forms, the two best known, or sound and electromagnetic variations.
43:49
Speaker 6: Sound carries very low concentrations of energy. This energy is
43:53
Speaker 6: absorbed by living tissue and converted into heat. Heat in
43:56
Speaker 6: itself can increase the mutation rate, but the effect is
43:59
Speaker 6: a small one. The body is effective massionary for keeping
44:02
Speaker 6: its temperature constant, and the gonads are not likely to
44:05
Speaker 6: suffer unduly from exposure to heat. Electromagnetic variation comes in
44:10
Speaker 6: a wide range of energies, with visible light the best
44:13
Speaker 6: known example of such variation, because we can detect it
44:15
Speaker 6: directly and with great sensitivity. About in the middle of
44:18
Speaker 6: the range. Electromagnetic variations less energetic than light, such as
44:22
Speaker 6: infrared waves and microwaves, are convertant to heat when absorbed
44:26
Speaker 6: by living tissue. Heat thus formed is sufficient to cause
44:29
Speaker 6: atoms and molecules to vibrate more rapidly, but this added
44:33
Speaker 6: vibration is not usually sufficient to pull molecules apart, and
44:36
Speaker 6: therefore does not bring about chemical changes. Light will bring
44:40
Speaker 6: about some chemical changes. It is energetic enough to cause
44:43
Speaker 6: a mixture of hydrogen and chlorine to explode. It will
44:46
Speaker 6: break up silver compounds and produce tiny black grains of
44:48
Speaker 6: metallic silver. The chemical basis of photography. Living tissue, however,
44:53
Speaker 6: is largely unaffected great now, the eye being one obvious exception.
44:58
Speaker 6: Ultravolet light, which is more energy and visible light, correspondingly,
45:01
Speaker 6: can bring about chemical changes more easily. It will redden
45:05
Speaker 6: the skin, stimulate the production of pigment, and break up
45:08
Speaker 6: certain steroid molecules to form vitamin D. It will even
45:11
Speaker 6: interfere with replication to some extent. At least, there is
45:14
Speaker 6: evidence that persistent exposure to sunlight brings about heightened tendency
45:18
Speaker 6: to skin cancer. Ultravolet light is not very penetrating, however,
45:22
Speaker 6: and its effects are confined to the skin. Electromagnetic variation
45:26
Speaker 6: more energetic than ultravolet light, such as X rays and
45:29
Speaker 6: gama RaSE carry sufficient concentrations of energy to bring about
45:32
Speaker 6: changes not only in molecules, but in the very structure
45:35
Speaker 6: of the atoms making up those molecules. Atoms consist of
45:40
Speaker 6: particles electrons, each carrying a negative electric charge. Atoms consist
45:44
Speaker 6: of particles electrons, each carrying a negative electric charge and
45:48
Speaker 6: circling a tiny, centrally located nucleus, which carries a positive
45:52
Speaker 6: electric charge. Ordinarily, the negative charges of the electrons just
45:55
Speaker 6: balance the positive charge in the nucleus, so that atoms
45:59
Speaker 6: and molecules tend be electrically neutral. An extraor gamma ray
46:03
Speaker 6: crashing into an atom will, however, jar electrons loose. What
46:07
Speaker 6: is left of the atom will carry a positive electric charge,
46:10
Speaker 6: with the charge size proportional to the number of electrons lost.
46:14
Speaker 6: An atom fragment carrying an electric charge is called an ion.
46:18
Speaker 6: X rays and gamma rays are there for examples of
46:20
Speaker 6: ionizing radiation. Radiations may consist of flying particles two and
46:26
Speaker 6: if these carry sufficient energy, they are also ionizing in character.
46:29
Speaker 6: Examples are cosmic rays, alpha rays, and beta rays. Cosmic
46:33
Speaker 6: rays are streams are positively charged nuclei, predominantly those of
46:37
Speaker 6: the element hydrogen. Alpha rays as streams are positively charged
46:40
Speaker 6: helium nuclear beta race as streams have negatively charged electrons.
46:46
Speaker 6: The individual particles contained in these rays may be referred
46:48
Speaker 6: to as cosmic particles, alpha particles and beta particles, respectively.
46:56
Speaker 6: Ionizing radiation is capable of imparting so much energy to
46:59
Speaker 6: molecules as to care them to vibrate themselves apart, producing
47:03
Speaker 6: not only ions but also high energy, uncharged molecular fragments
47:06
Speaker 6: called free radicals. The direct effect of ionizing radiation on
47:10
Speaker 6: chromosomes can be serious enough. Chemical bonds may be disrupted
47:13
Speaker 6: so that a chromosome struck by a higher energy wave
47:16
Speaker 6: or particle may break into fragments, even if the chromosome
47:19
Speaker 6: manages to remain intact. An individual gene long its length
47:23
Speaker 6: may be badly damaged, and a mutation may be produced.
47:26
Speaker 6: If only direct hits mattered, variation effects would be less
47:29
Speaker 6: dangerous than they are, since such direct hits are comparatively few. However,
47:34
Speaker 6: neo messis may also be deadly. A streaking bit of
47:37
Speaker 6: radiation may strike a water molecule near a gene and
47:40
Speaker 6: may break up the molecule to form a free radical.
47:43
Speaker 6: The free radical will be sufficiently energetic to bring about
47:45
Speaker 6: a chemical reaction with almost any molecule it strikes. If
47:50
Speaker 6: it happens to strike the neighboring gene before it has
47:52
Speaker 6: disposed off that energy, it will produce the mutation as
47:55
Speaker 6: surely as the original variation might have. Furthermore, ionizing variations,
48:00
Speaker 6: particularly of the electromagnetic variety, tend to be penetrating, so
48:03
Speaker 6: that the interior of the body is as exposed as
48:06
Speaker 6: is the surface. The gnats cannot hide from X rays,
48:09
Speaker 6: gamma rays of cosmic particles. All these radiations can bring
48:13
Speaker 6: about somatic mutations, all can cause cancer. For instance, what
48:18
Speaker 6: is verse All of them increase the rate of genetic mutations,
48:21
Speaker 6: so that their presence threatens generations and born as well
48:24
Speaker 6: as the individuals actually exposed. End of section nine Ionizing radiation.
48:37
Speaker 6: Section ten of the Genetic Effects of radiation. This is
48:40
Speaker 6: a LibriVox recording. All liberuvox recordings are in the public domain.
48:44
Speaker 6: For more information or to volunteer, please visit LibriVox dot org.
48:49
Speaker 6: Read by Yoganum. The Genetic Effects of radiation by Isaac
48:53
Speaker 6: Asimo and Theodosius Dobzanski Section ten. Background radiation ionizing radiation
49:02
Speaker 6: in low intensities is part of our natural environment. Such
49:06
Speaker 6: natural variations referred to as background radiation. Part of it
49:10
Speaker 6: arises from certain constituents of the soil. Atoms of the
49:13
Speaker 6: heavy metals uranium and thorium are constantly, though very slowly
49:17
Speaker 6: breaking down and in the process giving of alpha rays,
49:20
Speaker 6: beta rays, and gamma rays. These elements, where not among
49:23
Speaker 6: the most common, are very widely spread. Minerals containing small
49:27
Speaker 6: quantities of uranium and thorium are to be found nearly everywhere.
49:31
Speaker 6: In addition, all the Earth is bombarded with cosmic rays
49:34
Speaker 6: from outer space and with streams of I energy particles
49:37
Speaker 6: from the Sun. Various units can be used to measure
49:40
Speaker 6: the intensity of this background variation. Ron Gen, abbreviated small
49:45
Speaker 6: R and named in honor of the discoverer of X rays,
49:47
Speaker 6: Willem ron Gen, is a unit based on a number
49:51
Speaker 6: of ions produced by variation. Rather more convenient is another
49:54
Speaker 6: unit that has come more recently into prominence. This is
49:58
Speaker 6: the rad an abbreviation radiation absorbed dose. That is a
50:02
Speaker 6: measure of the amount of energy delivered to the body.
50:05
Speaker 6: Upon the absorption of a particular dose of ionizing radiation,
50:08
Speaker 6: one rat is very nearly equal to one draun gin.
50:11
Speaker 6: Since background radiation is undoubtedly one of the factors in
50:14
Speaker 6: producing spontaneous mutations, it is of interest to try to
50:17
Speaker 6: determine how much radiation a man or woman will have
50:20
Speaker 6: absorbed from the time he is first conceived to the
50:23
Speaker 6: time he conceives his own children. The average length of
50:26
Speaker 6: time between generations is taken to be about thirty years,
50:29
Speaker 6: so we can best express absorption of background radiation in
50:33
Speaker 6: units of rats per thirty years. Intensity of background radiation
50:37
Speaker 6: varies from place to place on the Earth for several reasons.
50:41
Speaker 6: Cosmic rays are deflected somewhat towards the magnetic poles by
50:44
Speaker 6: the Earth's magnetic field. We are also absorbed by the
50:47
Speaker 6: atmosphere to some extent. For this reason, people living in
50:50
Speaker 6: equatorial regions are less exposed to cosmic rays than those
50:53
Speaker 6: in polar regions, and those in the planes with a
50:56
Speaker 6: greater thickness of atmosphere above them are less exposed than
50:59
Speaker 6: those on high platus. Then two radiactive minerals may be
51:04
Speaker 6: spread widely, but they are not spread evenly where they
51:07
Speaker 6: are concentrated to a greater extent than usual, background radiation
51:11
Speaker 6: is abnormally high. Thus, an inhabitant of Harrisburg, Pennsylvania, may
51:16
Speaker 6: absorb two point six four rats per thirty years, while
51:19
Speaker 6: one of Denver, Colorado, a mile high at the foot
51:22
Speaker 6: of the Rockies, may absorb five point zero four rats
51:25
Speaker 6: per thirty years. Greater extremes are encountered at such places
51:29
Speaker 6: as Kerala, India, where nearby soil which and thorium minerals
51:33
Speaker 6: so increases the intensity of background radiation that as much
51:36
Speaker 6: as eighty four rats may be absorbed in thirty years.
51:40
Speaker 6: In addition to high energy variation from the outside, there
51:43
Speaker 6: are sources within the body itself. Some of the potassium
51:46
Speaker 6: and carbon atoms of our body are inevitably radioactive as
51:50
Speaker 6: much as point fere rat, but thirty ers arises from
51:52
Speaker 6: this source. Rats and roun gens are not completely satisfactory
51:56
Speaker 6: units in estimating the biological effects of variation. Some types
51:59
Speaker 6: of way diation, those made up of comparatively large particles,
52:02
Speaker 6: for instance, are more effective in producing ions and bring
52:05
Speaker 6: about molecular changes with greater ease than do electromagnetic radiation,
52:09
Speaker 6: delivering equal energy to the body. Thus, if one grad
52:13
Speaker 6: of alpha particles is absorbed by the body, ten to
52:16
Speaker 6: twenty times as much biological effect is produced as there
52:19
Speaker 6: would be in the absorption of one grad of X rays,
52:22
Speaker 6: gamma race a beta particles. Sometimes, then when speaks of
52:26
Speaker 6: the relative biological effectiveness are bee of radiation or the
52:31
Speaker 6: orange and equivalent man rerim rad of X rays, gamma
52:35
Speaker 6: race or beta particles as a rem of one, while
52:38
Speaker 6: a rad of alpha particles as a rem of ten
52:40
Speaker 6: to twenty. If we allow for the effect of the
52:43
Speaker 6: larger particles, which are not very common in ordinary conditions,
52:47
Speaker 6: we can estimate that the gonads of the average human
52:49
Speaker 6: being receive a total dose of natural radiation of about
52:52
Speaker 6: three rems per thirty years. This is just about an
52:55
Speaker 6: irreducible minimum. The end of section ten background radio.
53:04
Speaker 7: Section eleven of the Genetic Effects of radiation. This is
53:08
Speaker 7: a LibriVox recording. All LibriVox recordings are in the public domain.
53:12
Speaker 7: For more information or to volunteer, please visit LibriVox dot org.
53:16
Speaker 7: Read by Kubi The Genetic Effects of Radiation by Isaac
53:20
Speaker 7: Asimov and Theodosius Dobzhanski. Man made radiation. Man began to
53:25
Speaker 7: add to the background radiation in the eighteen nineties. In
53:28
Speaker 7: eighteen ninety five, X rays were discovered and since then
53:32
Speaker 7: have become increasingly useful in medical diagnosis and therapy and
53:35
Speaker 7: in industry. In eighteen ninety six, radioactivity was discovered and
53:40
Speaker 7: radioactive substances were concentrated in laboratories in order that they
53:43
Speaker 7: might be studied. In nineteen thirty four, it was found
53:46
Speaker 7: that radioactive forms of non radioactive elements radioisotopes could be formed,
53:51
Speaker 7: and their use came to be widespread in universities, hospitals,
53:55
Speaker 7: and industries. Then, in nineteen forty five, the nuclear bomb
53:58
Speaker 7: was developed. With the the uranium or plutonium fission that
54:01
Speaker 7: produces a nuclear explosion, there is an accompaniment of intense
54:05
Speaker 7: gamma radiation. In addition, a variety of radioisotopes are left
54:09
Speaker 7: behind in the form of the residue fission fragments of
54:12
Speaker 7: the fissioning atoms. These fission fragments are distributed widely in
54:16
Speaker 7: the atmosphere, Some rise high into the stratosphere and descendants
54:19
Speaker 7: fall out over the succeeding months and years. It is
54:22
Speaker 7: hard to try to estimate how much additional radiation is
54:25
Speaker 7: being absorbed by human beings. Out of these man made sources,
54:29
Speaker 7: fallout is not uniformly spread over the Earth, but as
54:32
Speaker 7: higher in those latitudes where nuclear bombs have been most
54:35
Speaker 7: frequently tested. Then too, people in industries and research who
54:38
Speaker 7: are involved with the use of radioisotopes and people in
54:41
Speaker 7: medical centers who constantly deal with X rays are likely
54:44
Speaker 7: to get more exposure than others. These adjects of modern
54:48
Speaker 7: science and medicine are more common and widespread and technologically
54:51
Speaker 7: advanced countries than elsewhere, and nuclear bombs have most often
54:55
Speaker 7: been exploded in just those latitudes where the advanced countries
54:58
Speaker 7: are to be found. Attempts have been made to work
55:00
Speaker 7: out estimates of this exposure. One estimate involving a number
55:04
Speaker 7: of technologically advanced countries, including the United States, showed that
55:08
Speaker 7: an average of somewhere between zero point zero two and
55:11
Speaker 7: zero point one eight RIM per year was absorbed as
55:13
Speaker 7: a result of radiations, usually X rays used in medical
55:16
Speaker 7: diagnosis and therapy. Occupational exposure added on the average not
55:21
Speaker 7: more than zero point zero zero three RIM, though the
55:24
Speaker 7: individuals constantly exposed in the course of their work would
55:27
Speaker 7: naturally absorb considerably more than this overall average. On the whole,
55:31
Speaker 7: the highest absorption was found, as was to be expected
55:35
Speaker 7: in the United States. If these findings are expanded to
55:38
Speaker 7: cover a thirty year period, assuming the absorption will remain
55:41
Speaker 7: the same from year to year, it turns out that
55:43
Speaker 7: the average absorption of man made radiation in the nations
55:46
Speaker 7: studied varies from zero point six rim to five point
55:49
Speaker 7: five rims per thirty years per individual. Considering the higher
55:53
Speaker 7: figure to be applicable to the United States, it would
55:56
Speaker 7: seem that man made radiation from all sources is now
55:59
Speaker 7: being absorbed at nearly twice the rate that natural radiation is.
56:03
Speaker 7: To put it another way, Americans are just about tripling
56:06
Speaker 7: their radiation dosage by reason of the human activities that
56:09
Speaker 7: are now adding man made radiation to the natural supply.
56:13
Speaker 7: By far. The major part of this additional dosage is
56:16
Speaker 7: the result of the use of X rays in searching
56:18
Speaker 7: for decayed teeth, broken bones, long lesions, swallowed objects, and
56:23
Speaker 7: so on.
56:24
Speaker 6: End of section eleven, Section twelve of the Genetic Effix
56:33
Speaker 6: of Radiation. This is a LIBERTYVOX recording. All liberywalx recordings
56:37
Speaker 6: are in the public domain. For more information or to volunteer,
56:40
Speaker 6: please visit libertyvox dot org read by Yoganan The Genetic
56:45
Speaker 6: Effects of Radiation by Isaac Asimov and Theodosius Dubzonski. Dose
56:51
Speaker 6: and Consequence radiation sickness, The danger of the individual as
56:57
Speaker 6: a result of overexposure to high energy radiation was understood
57:00
Speaker 6: fairly soon, but not before some tragic experiences were recorded.
57:05
Speaker 6: One of the early workers with radiactive materials, pure Curi,
57:09
Speaker 6: deliberately exposed a patch of the skin to the action
57:11
Speaker 6: of radioactive radiations and obtained a serious and slow healing burn.
57:15
Speaker 6: His wife, Marie Curie, and their daughter Iran Juliot Curie,
57:20
Speaker 6: who spent their lives working with radiactive materials, both died
57:24
Speaker 6: of leukemia, very possibly as a result of cumulative exposure
57:27
Speaker 6: to radiation. Other research workers in the field died of cancer.
57:31
Speaker 6: Before the full necessity of extreme caution was understood, the
57:35
Speaker 6: damage done to human beings with radiation could first be
57:38
Speaker 6: studied on a large scale among the survivors of the
57:41
Speaker 6: nuclear bombings of Hiroshima and Nagasaki in nineteen forty five. Here,
57:45
Speaker 6: marked symptoms of radiation sickness were observed. This sickness often
57:49
Speaker 6: leads to death, though a slow recovery is sometimes possible.
57:53
Speaker 6: In general, high energy radiation damage is a complex molecules
57:57
Speaker 6: within a cell interfering with its chemical missionary to the
58:00
Speaker 6: point in extreme cases of killing it. Thus, cancers which
58:04
Speaker 6: cannot safely be reached with the surgeon's knife are sometimes
58:07
Speaker 6: exposed to high energy radiation in the hope that the
58:09
Speaker 6: cancer cells will be effectively killed. In that manner. The
58:13
Speaker 6: delicate structure of the genes and chromosomes is particularly vulnerable
58:16
Speaker 6: to the impact of high energy radiation. Chromosomes can be
58:19
Speaker 6: broken by such variation, and this is the main cause
58:22
Speaker 6: of actual cell death. A cell that is not killed
58:25
Speaker 6: outright by radiation may nevertheless be so damaged as to
58:29
Speaker 6: be unable to undergo replication in mitosis. If a cell
58:33
Speaker 6: is of a type that will not, in the codes
58:35
Speaker 6: of nature, undergo division, the destruction of the mitosis missionary
58:38
Speaker 6: is not in itself fatal to the organism. A creature
58:42
Speaker 6: like drosophilia, which in its adult stage has very few
58:45
Speaker 6: cell divisions going on among the ordinary cells of its body,
58:48
Speaker 6: can survive radiation doses a hundred times as great as
58:52
Speaker 6: would suffice to kill a man. In a human being, However,
58:56
Speaker 6: even in an adult who is no longer experiencing overall growth.
58:59
Speaker 6: There are many toshues whose cells must undergo division throughout life.
59:03
Speaker 6: Hair and fingernails grow constantly as a result of cell
59:06
Speaker 6: division at their roots. The outer layers of skin are
59:09
Speaker 6: steadily lost through abrasion and are replaced through constant cell
59:12
Speaker 6: division in the deeper layers. The same is true of
59:14
Speaker 6: the lining of the mouth, throat, stomach, and interstines. Two
59:18
Speaker 6: blood cells are continually breaking up and must be replaced
59:21
Speaker 6: in vast numbers. If radiation kills the mechanism of division
59:25
Speaker 6: in only some of these cells, it is possible that
59:27
Speaker 6: those that remain reasonably intact can divide and eventually replace
59:31
Speaker 6: or do the work of those that can no longer divide.
59:34
Speaker 6: In that case, the symptoms of radiation sickness are relatively
59:36
Speaker 6: mild in the first place, and eventually disappear past a
59:40
Speaker 6: certain critical point. When too many cells are made incapable
59:43
Speaker 6: of division, this is no longer possible. The symptoms which
59:46
Speaker 6: show up in the growing tissues, particularly as in the
59:49
Speaker 6: loss of hair, the misshaping or loss of fingernails, the
59:52
Speaker 6: reddening and hemorrhaging of skin, the alteration of the mouth
59:56
Speaker 6: and the lowering of the blood cell count grow steadily
59:59
Speaker 6: more severe and death follows. End of section twelve Radiation sickness.
1:00:10
Speaker 8: Section thirteen of the Genetic Effects of radiation.
1:00:15
Speaker 9: This is a LibriVox recording.
1:00:17
Speaker 8: All LibriVox recordings are in the public domain. For more
1:00:21
Speaker 8: information or to volunteer, please visit LibriVox dot org. Read
1:00:26
Speaker 8: by tr Love of Pleasant Hill, California. The Genetic Effects
1:00:32
Speaker 8: of Radiation by Isaac Asimov and Theodosius Dobzhansky. Section thirteen
1:00:39
Speaker 8: Radiation and mutation. Where radiation is insufficient to render a
1:00:45
Speaker 8: cell incapable of division, it may still induce mutations, and
1:00:50
Speaker 8: it is in this fashion that skin cancer, leukemia, and
1:00:54
Speaker 8: other disorders may be brought about. Studies at the California
1:00:58
Speaker 8: Institute of Technology furnish information on the nature of radiation
1:01:03
Speaker 8: effects on genes. Mutations can be brought about in the
1:01:08
Speaker 8: sex cells two, of course, and when this happens, it
1:01:11
Speaker 8: is succeeding generations that are affected, and not merely the
1:01:16
Speaker 8: exposed individual. Indeed, where the sex cells are concerned, the
1:01:21
Speaker 8: relatively mild effect of mutation is more serious than the
1:01:25
Speaker 8: drastic one of nondivision. A fertilized ovum that cannot divide
1:01:30
Speaker 8: eventually dies and does no harm. One that can divide
1:01:35
Speaker 8: but is altered may give rise to an individual with
1:01:39
Speaker 8: one of the usual kinds of major or minor physical defects.
1:01:44
Speaker 9: The effect of high.
1:01:45
Speaker 8: Energy radiation on the genetic mechanism was first demonstrated experimentally
1:01:52
Speaker 8: in nineteen twenty seven by Mueller.
1:01:55
Speaker 9: Using Drosophila.
1:01:56
Speaker 8: He showed that after large doses of X rays, flies
1:02:00
Speaker 8: experienced many more lethal mutations per chromosome than did similar
1:02:06
Speaker 8: flies not exposed to radiation. The drastic differences he observed
1:02:12
Speaker 8: proved the connection between radiation and mutation at once. Later
1:02:17
Speaker 8: experiments by Mueller and by others showed that the number
1:02:21
Speaker 8: of mutations was directly proportional to the quantity of radiation absorbed.
1:02:28
Speaker 8: Doubling the quantity of radiation absorbed doubled the number of mutations,
1:02:33
Speaker 8: tripling the one tripled the other, and so on. This
1:02:38
Speaker 8: means that if the number of mutations is plotted against
1:02:41
Speaker 8: the amount of radiation absorbed, a straight line can be drawn.
1:02:46
Speaker 8: It is generally believed that the straight line continues all
1:02:50
Speaker 8: the way down without deviation to very low radiation absorptions.
1:02:56
Speaker 8: This means there is no threshold for the mutation effect
1:03:00
Speaker 8: of radiation. No matter how small a dosage of radiation
1:03:04
Speaker 8: the gonands receive. This will be reflected in a proportionately
1:03:09
Speaker 8: increased likelihood of mutated sex cells, with effects that will
1:03:13
Speaker 8: show up in succeeding generations. In this respect, the genetic
1:03:19
Speaker 8: effect of radiation is quite different from the somatic effect.
1:03:23
Speaker 8: A small dose of radiation may affect growing tissues and
1:03:28
Speaker 8: prevent a small proportion of the cells of those tissues
1:03:31
Speaker 8: from dividing. The remaining unaffected cells take up the slack. However,
1:03:38
Speaker 8: and if the proportion of affected cells is small enough,
1:03:42
Speaker 8: symptoms are not visible and never become visible. There is
1:03:47
Speaker 8: thus a threshold effect. The radiation absorbed must be more
1:03:51
Speaker 8: than a certain amount before any somatic symptoms are manifest.
1:03:56
Speaker 8: Matters are quite different where the genetic effect is concerned.
1:04:01
Speaker 8: If a sex cell is damaged, and if that sex
1:04:04
Speaker 8: cell is one of the pair that goes into the
1:04:07
Speaker 8: production of a fertilized ovum, a damaged organism results. There
1:04:13
Speaker 8: is no margin for correction. There is no unaffected cell
1:04:17
Speaker 8: that can take over the work of the damaged sex
1:04:20
Speaker 8: cell once fertilization has taken place.
1:04:24
Speaker 9: Suppose only one sex.
1:04:25
Speaker 8: Cell out of a million is damaged. If so, a
1:04:29
Speaker 8: damaged sex cell will on the average take part in
1:04:34
Speaker 8: one out of every million fertilizations, and when it is used,
1:04:39
Speaker 8: it will not matter that there are nine hundred ninety
1:04:42
Speaker 8: nine thousand, nine hundred and ninety nine perfectly good sex cells.
1:04:47
Speaker 9: That might have been used. It was the damage cell
1:04:50
Speaker 9: that was used. This is why there is no threshold in.
1:04:54
Speaker 8: The genetic effect of radiation, and why there is no
1:04:58
Speaker 8: safe amount of radiations. In so far as genetic effects
1:05:02
Speaker 8: are concerned. However small the quantity of radiation absorbed, mankind
1:05:08
Speaker 8: must be prepared to pay the price in a corresponding
1:05:11
Speaker 8: increase of the genetic load. If the straight line obtained
1:05:16
Speaker 8: by plotting mutation rate against radiation dose is followed down
1:05:21
Speaker 8: to a radiation dose of zero, it is found that
1:05:24
Speaker 8: the line strikes the vertical axis slightly above the origin.
1:05:29
Speaker 8: The mutation rate is more than zero even when the
1:05:33
Speaker 8: radiation dose is zero. The reason for this is that
1:05:37
Speaker 8: it is the dose of man made radiation that is
1:05:40
Speaker 8: being considered. Even when man made radiation is completely absent,
1:05:45
Speaker 8: there still remains the natural background radiation. It is possible
1:05:51
Speaker 8: in this manner to determine that background radiation accounts for
1:05:55
Speaker 8: considerably less than one percent of the spontaneous mutations that
1:06:00
Speaker 8: take place. The other mutations must arise out of chemical misadventures,
1:06:06
Speaker 8: out of the random heat, jiggling of molecules, and so on. These,
1:06:11
Speaker 8: it can be presumed, will remain constant when the radiation
1:06:15
Speaker 8: does is increased. This is a hopeful aspect of the situation,
1:06:20
Speaker 8: for it means that if the background radiation is doubled
1:06:24
Speaker 8: or tripled for mankind as a whole, only that small
1:06:28
Speaker 8: portion of the spontaneous mutation rate that is due to
1:06:33
Speaker 8: the background radiation will be.
1:06:35
Speaker 9: Doubled or tripled.
1:06:37
Speaker 8: Let us suppose, for instance, that fully one percent of
1:06:41
Speaker 8: the spontaneous mutations occurring in mankind is due to background radiation.
1:06:47
Speaker 8: In that case, the tripling of the background radiation produced
1:06:52
Speaker 8: in the United States by man made causes see table
1:06:56
Speaker 8: will triple that one percent. In place of ninety nine
1:07:00
Speaker 8: non radiational mutations plus one radiational, we would have ninety
1:07:06
Speaker 8: nine plus three. The total number of mutations would increase
1:07:11
Speaker 8: from one hundred to one hundred two, an increase of
1:07:14
Speaker 8: two percent, not an increase of two hundred percent that
1:07:19
Speaker 8: one would expect if all spontaneous mutations were caused by
1:07:23
Speaker 8: background radiation. Table Radiation exposures in the United States open
1:07:30
Speaker 8: footnote estimated average exposures to the Gonans based on nineteen
1:07:36
Speaker 8: sixty three report of Federal Radiation Council.
1:07:39
Speaker 9: Close footnote.
1:07:41
Speaker 8: Natural sources millirems A external to the body one from
1:07:47
Speaker 8: cosmic radiation fifty point zero two from the earth, forty
1:07:53
Speaker 8: seven point zero three from building materials three point zero
1:07:58
Speaker 8: B inside the body one inhalation of air five point
1:08:04
Speaker 8: zero two elements found naturally in human tissues twenty one
1:08:10
Speaker 8: point zero Total natural sources one hundred twenty six point
1:08:16
Speaker 8: zero millirems. Man made sources A medical procedures one diagnostic
1:08:23
Speaker 8: X rays fifty point zero two, radiotherapy X ray radio
1:08:30
Speaker 8: isotopes ten point zero three, internal diagnosis therapy one point
1:08:37
Speaker 8: zero subtotal sixty one point zero millirems. B atomic energy
1:08:44
Speaker 8: industry laboratories zero point two C, luminous watch dials, television tubes,
1:08:52
Speaker 8: radioactive industrial wastes, et cetera two point zero D radioactive
1:08:59
Speaker 8: fallout four point zero subtotal six point two millirems. Total
1:09:06
Speaker 8: man made sources sixty seven point two millirems overall total
1:09:12
Speaker 8: one hundred ninety three point two millirems end of section
1:09:17
Speaker 8: thirteen Section fourteen of The Genetic Effects of Radiation. This
1:09:28
Speaker 8: is a LibriVox recording. All LibriVox recordings are in the
1:09:32
Speaker 8: public domain. For more information or to volunteer, please visit
1:09:37
Speaker 8: LibriVox dot org.
1:09:39
Speaker 9: Read by T. R.
1:09:40
Speaker 8: Love of Pleasant Hill, California. The Genetic Effects of Radiation
1:09:45
Speaker 8: by Isaac Asimov and Theodosius Dobzanski, Section fourteen dosige rates.
1:09:54
Speaker 8: Another difference between the genetic and somatic effects of radiation
1:09:58
Speaker 8: rests in the response to changes in the rate at
1:10:02
Speaker 8: which radiation is absorbed. It makes a considerable difference to
1:10:07
Speaker 8: the body whether a large dose of radiation is absorbed
1:10:10
Speaker 8: over the space of a few minutes or a few years.
1:10:15
Speaker 8: When a large dose is absorbed over a short interval
1:10:18
Speaker 8: of time, so many of the growing tissues lose the
1:10:22
Speaker 8: capacity for cell division that death may follow if the
1:10:27
Speaker 8: same dose is delivered over years. Only a small bit
1:10:30
Speaker 8: of radiation is absorbed on any given day, and only
1:10:34
Speaker 8: small proportions of growing cells lose the capacity for division
1:10:39
Speaker 8: at any one time. The unaffected cells will continually make
1:10:44
Speaker 8: up for this and will replace the affected ones. The
1:10:48
Speaker 8: body is, so to speak, continually repairing the radiation damage,
1:10:53
Speaker 8: and no serious symptoms will develop. Then two, if a
1:10:57
Speaker 8: moderate dose is delivered, the body may show visible symptoms
1:11:01
Speaker 8: of radiation sickness, but can recover. It will then be
1:11:06
Speaker 8: capable of withstanding another moderate dose, and so on. The
1:11:11
Speaker 8: situation is quite different with respect to the genetic effects,
1:11:15
Speaker 8: at least as far as experiments with drosophila and bacteria
1:11:20
Speaker 8: seem to show. Even the smallest doses will produce a
1:11:24
Speaker 8: few mutations in the chromosomes of those cells in the
1:11:28
Speaker 8: gonads that eventually develop into sex cells. The affected gonad
1:11:33
Speaker 8: cells will continue to produce sex cells with those mutations
1:11:38
Speaker 8: for the rest of the life of the organism. Every
1:11:42
Speaker 8: tiny bit of radiation adds to the number of mutated
1:11:45
Speaker 8: sex cells being constantly produced. There is no recovery because
1:11:51
Speaker 8: the sex cells after formation do not work in cooperation,
1:11:55
Speaker 8: and affected cells are not replaced by those that are unaffected.
1:12:00
Speaker 8: This means, judging by the experiments on lower creatures, that
1:12:04
Speaker 8: what counts where genetic damage is in question is not
1:12:08
Speaker 8: the rate at which radiation is absorbed, but the total
1:12:12
Speaker 8: sum of radiation every exposure and organism experiences, however small,
1:12:19
Speaker 8: adds its bit of damage. Accepting this hard view, it
1:12:24
Speaker 8: would seem important to make every effort to minimize radiation
1:12:28
Speaker 8: exposure for the population generally. Since most of the man
1:12:32
Speaker 8: made increase in background radiation is the result of the
1:12:36
Speaker 8: use of X rays in medical diagnosis and therapy, many
1:12:40
Speaker 8: geneticists are looking at this with suspicion and concern. No
1:12:45
Speaker 8: one suggests that their use be abandoned, for certainly such
1:12:50
Speaker 8: techniques are important in the saving of life and the
1:12:53
Speaker 8: mitigation of suffering. Still, X rays ought not to be
1:12:57
Speaker 8: used lightly or routinely. As a matter of course, it
1:13:02
Speaker 8: might seem that X rays applied to the jaw or
1:13:04
Speaker 8: the chest would not affect the gonads. And this might
1:13:08
Speaker 8: be so if all the X rays could indeed be
1:13:11
Speaker 8: confined to the portion of the body at which they
1:13:14
Speaker 8: are aimed. Unfortunately, X rays do not uniformly travel a
1:13:20
Speaker 8: straight line in passing through matter. They are scattered to
1:13:24
Speaker 8: a certain extent. If a stream of X rays passes
1:13:27
Speaker 8: through the body anywhere, or even through objects near the body,
1:13:32
Speaker 8: some X rays will be scattered through the gonants. It
1:13:36
Speaker 8: is for this reason that some geneticists suggests that the
1:13:40
Speaker 8: history of exposure to X rays be kept carefully for
1:13:44
Speaker 8: each person. A decision on a new exposure would then
1:13:48
Speaker 8: be determined not only by the current situation, but by
1:13:52
Speaker 8: the individual's past history. Such considerations were also an important
1:13:57
Speaker 8: part of the driving force behind the movement to end
1:14:01
Speaker 8: atmospheric testing of nuclear bombs. While the total addition to
1:14:05
Speaker 8: the background radiation resulting from such tests is small, the
1:14:10
Speaker 8: prospect of continued accumulation is unpleasant. What's more, whereas X
1:14:17
Speaker 8: rays used in diagnosis and therapy have a humane purpose
1:14:21
Speaker 8: and chiefly affect the patient who hopes to be helped
1:14:25
Speaker 8: in the process, nuclear fallout affects all of humanity without distinction,
1:14:31
Speaker 8: and seems to many people to have as its end
1:14:35
Speaker 8: only the promise of a totally destructive nuclear war.
1:14:40
Speaker 9: It is not to be expected that the large.
1:14:42
Speaker 8: Majority of humanity that makes up the populations outside the
1:14:47
Speaker 8: United States, Great Britain, France, China, and the Soviet Union
1:14:53
Speaker 8: can be expected to accept stoically the risk of even
1:14:57
Speaker 8: limited quantities of genetic damage out of any feeling of
1:15:01
Speaker 8: loyalty to nations not their own. Even within the populations
1:15:06
Speaker 8: of the three major nuclear powers. There are strong feelings
1:15:10
Speaker 8: that the possible benefits of nuclear testing do not balance
1:15:14
Speaker 8: the certain dangers. Public opinion throughout the world is a
1:15:19
Speaker 8: key factor, then, in enforcing the nuclear test Ban Treaty
1:15:24
Speaker 8: signed by the governments of the United States, Great Britain
1:15:28
Speaker 8: and the Soviet Union on October tenth, nineteen sixty three.
1:15:33
Speaker 8: End of section fourteen. Section fifteen of the Genetic Effects
1:15:43
Speaker 8: of Radiation.
1:15:45
Speaker 9: This is a LibriVox recording.
1:15:47
Speaker 8: All LibriVox recordings are in the public domain. For more
1:15:51
Speaker 8: information or to volunteer, please.
1:15:53
Speaker 9: Visit LibriVox dot org. Read by T. R.
1:15:57
Speaker 8: Love of Pleasant Hill, California. The Genetic Effects of Radiation
1:16:03
Speaker 8: by Isaac Asimov and Theodosius Dobzansky, Section fifteen effects on mammals.
1:16:11
Speaker 8: Although genetic findings on such comparatively simple creatures as fruit
1:16:16
Speaker 8: flies and bacteria seem to apply generally to all forms
1:16:20
Speaker 8: of life, it seems unsafe to rely on these findings
1:16:24
Speaker 8: completely in anything as important as possible genetic damage to
1:16:29
Speaker 8: man through radiation. During the nineteen fifties and nineteen sixties, therefore,
1:16:36
Speaker 8: there have been important studies on mice, particularly by W. L.
1:16:41
Speaker 8: Russell at Oakridge National laboratory, Oakridge, Tennessee. While not as
1:16:47
Speaker 8: short lived or as second as fruit flies, mice can
1:16:50
Speaker 8: nevertheless produce enough young over a reasonable period of time
1:16:55
Speaker 8: to yield statistically useful results. Experimenters have worked with hundreds
1:17:01
Speaker 8: of thousands of offspring born of mice that have been
1:17:05
Speaker 8: irradiated with gamma rays and X rays in different amounts
1:17:09
Speaker 8: and at different intensities, as well as with additional hundreds
1:17:14
Speaker 8: of thousands born to mice that were not irradiated. Since mice,
1:17:19
Speaker 8: like men, are mammals, results gained by such experiments are
1:17:23
Speaker 8: particularly significant. Mice are far closer to man in the
1:17:28
Speaker 8: scheme of life than is any other creature that has
1:17:31
Speaker 8: been studied genetically on a large scale, and their reactions,
1:17:36
Speaker 8: one might cautiously assume, are likely to be closer to
1:17:39
Speaker 8: those that would be found in man. Almost at once
1:17:44
Speaker 8: when the studies began, it turned out that mice were
1:17:47
Speaker 8: more susceptible to genetic damage than fruitflies were. The induced
1:17:53
Speaker 8: mutation rate per gene seems to be about fifteen times
1:17:57
Speaker 8: that found in Drosophila for comparable X ray doss.
1:18:02
Speaker 9: The only safe course.
1:18:03
Speaker 8: For mankind, then, is to air if it must strongly
1:18:07
Speaker 8: on the side of conservatism. Once we have decided what
1:18:11
Speaker 8: might be safe on the basis of Drosophilus studies, we
1:18:15
Speaker 8: ought then to tighten precautions several notches by remembering that
1:18:19
Speaker 8: we are very likely more vulnerable than fruitflies are counteracting.
1:18:24
Speaker 8: The depressing nature of this finding was that of a later,
1:18:28
Speaker 8: quite unexpected discovery. It was well established that in fruit
1:18:33
Speaker 8: flies and other simple organisms, it was the total dosage
1:18:38
Speaker 8: of absorbed radiation that counted, and that whether this was
1:18:42
Speaker 8: delivered quickly or slowly did not matter.
1:18:46
Speaker 9: This proved to be not so in the case of mice.
1:18:49
Speaker 9: In male mice, a radiation dose.
1:18:51
Speaker 8: Delivered at the rate of zero point zero zero nine
1:18:54
Speaker 8: rad per minute produced only from one quarter to one
1:18:58
Speaker 8: third as many mutations as did the same total dose
1:19:02
Speaker 8: delivered at ninety rads per minute. In the male cells
1:19:06
Speaker 8: in the gonads are constantly dividing.
1:19:08
Speaker 9: To produce sex cells, the latter are produced by the billions.
1:19:13
Speaker 8: It might be then that at low radiation dose rates,
1:19:17
Speaker 8: a few of the gonad cells are damaged, but that
1:19:20
Speaker 8: the undamaged ones produce a flood of sperm cells.
1:19:24
Speaker 9: Drowning out the few produced by.
1:19:26
Speaker 8: The damaged gonad cells. The same radiation dose delivered in
1:19:31
Speaker 8: a short time might, however, damage so many of the
1:19:35
Speaker 8: gonad cells as to make the damaged sex cells much.
1:19:39
Speaker 9: More difficult to flood out.
1:19:41
Speaker 8: A second possible explanation is that there is present within
1:19:45
Speaker 8: the cells themselves, some process that tends to repair damage
1:19:50
Speaker 8: to the cells and to counteract mutations. It might be
1:19:54
Speaker 8: a slow working, laborious process that could keep up with
1:19:58
Speaker 8: the damage inflicted at low dosage rates, but not at
1:20:02
Speaker 8: high ones. High dosage rates might even damage the repair
1:20:06
Speaker 8: mechanism itself. That too, would account for the fewer mutations
1:20:11
Speaker 8: at low dosage rates than at high ones. To check
1:20:15
Speaker 8: which of the two possible explanations was nearer the truth,
1:20:19
Speaker 8: Russell performed similar.
1:20:20
Speaker 9: Tests on female mice.
1:20:22
Speaker 8: In the female mouse, or the female human being for
1:20:25
Speaker 8: that matter, the egg cells have completed almost all their
1:20:29
Speaker 8: divisions before the female is born. There are only so
1:20:34
Speaker 8: many cells in the female gonants that can give rise
1:20:38
Speaker 8: to egg cells, and each one gives rise to only
1:20:41
Speaker 8: a single egg cell. There is no possibility of damaged
1:20:45
Speaker 8: egg cells being drowned out by floods of undamaged ones
1:20:50
Speaker 8: because there are no floods yet. It was found that
1:20:54
Speaker 8: in the female mouse, the mutation rate also dropped when
1:20:58
Speaker 8: the radiation dose rate was decreased. In fact, it dropped
1:21:02
Speaker 8: even more drastically than was the case in the male mouse. Apparently,
1:21:07
Speaker 8: then there must be actual repair within the cell. There
1:21:11
Speaker 8: must be some chemical mechanism inside the cell capable of
1:21:15
Speaker 8: counteracting radiation damage to some extent. In the female mouse,
1:21:20
Speaker 8: the mutation rate drops very low as the radiation dose
1:21:24
Speaker 8: rate drops, so that it would seem that almost all
1:21:28
Speaker 8: mutations might be repaired given enough time. In the male
1:21:33
Speaker 8: the mutation rate drops only so far and no farther,
1:21:37
Speaker 8: so that some mutations about one third is the best
1:21:40
Speaker 8: estimate so far, cannot be repaired. If this is also
1:21:45
Speaker 8: true in the human being, and it is at least
1:21:48
Speaker 8: reasonably likely that it is, then the greater vulnerability of
1:21:53
Speaker 8: our genes, as compared with those of fruitflies, is at
1:21:57
Speaker 8: least partially made up for by our.
1:21:59
Speaker 9: Graineaterability to repair the damage.
1:22:03
Speaker 8: This opens a door for the future too, the workings
1:22:07
Speaker 8: of the gene repair mechanism, ought it is to be
1:22:10
Speaker 8: hoped eventually to be puzzled out. When it is, methods
1:22:15
Speaker 8: may be discovered for reinforcing that mechanism, speeding it and
1:22:20
Speaker 8: increasing its effectiveness. We may then find ourselves no longer
1:22:25
Speaker 8: completely helpless in the face of genetic damage or even
1:22:29
Speaker 8: of radiation sickness. On the other hand, it is only
1:22:33
Speaker 8: fair to point out that the foregoing appraisal may be
1:22:37
Speaker 8: an over optimistic view. Russell's experiments involve just seven genes,
1:22:44
Speaker 8: and it is possible that these are not representative of
1:22:47
Speaker 8: the thousands that exist altogether.
1:22:51
Speaker 9: While the work done so far is most.
1:22:53
Speaker 8: Suggestive and interesting, much research remains to be carried out.
1:22:58
Speaker 8: If then we cannot help hoping that natural devices for
1:23:02
Speaker 8: counteracting radiation damage may be developed in the future, we
1:23:07
Speaker 8: must for the present remain rigidly cautious.
1:23:11
Speaker 9: End of section fifteen.
1:23:18
Speaker 8: Section sixteen of The Genetic Effects of Radiation. This is
1:23:23
Speaker 8: a LibriVox recording. All LibriVox recordings are in the public domain.
1:23:28
Speaker 8: For more information or to volunteer, please visit LibriVox dot org.
1:23:34
Speaker 9: Read by T. R.
1:23:35
Speaker 8: Love of Pleasant Hill, California. The Genetic Effects of Radiation
1:23:41
Speaker 8: by Isaac Asimov and theodocious Dobzanski. Section sixteen conclusion, it
1:23:49
Speaker 8: is unrealistic to suppose that all sources of mad made
1:23:53
Speaker 8: radiation should be abolished. The good they do now, the
1:23:58
Speaker 8: greater good they will do in the future cannot be abandoned.
1:24:02
Speaker 8: It is, however, reasonable to expect that the present Nuclear
1:24:06
Speaker 8: Test Band Treaty will continue, and that nations such as
1:24:11
Speaker 8: France and China, which have nuclear capabilities but are not
1:24:15
Speaker 8: signatories of the treaty, will eventually sign It is also
1:24:20
Speaker 8: reasonable to expect that X ray diagnosis and therapy will
1:24:25
Speaker 8: be carried on with the greatest circumspection, and that the
1:24:29
Speaker 8: use of radiation in industry and research will be carried
1:24:33
Speaker 8: on with great care and with the use of ample shielding.
1:24:37
Speaker 8: As long as man made radiation exists, there will be
1:24:40
Speaker 8: some absorption of it by human beings. The advantages of
1:24:45
Speaker 8: its use in our modern society are such that we
1:24:48
Speaker 8: must be prepared to pay some price. It is not
1:24:52
Speaker 8: a matter of callousness. We have come to depend a
1:24:55
Speaker 8: great deal for comfort and even for extended life upon
1:24:59
Speaker 8: the achieved of our technology, and any serious crippling of
1:25:03
Speaker 8: that technology will cost us lives.
1:25:07
Speaker 9: An attempt must be.
1:25:08
Speaker 8: Made to balance the values of radiation against its dangers.
1:25:12
Speaker 8: We must balance lives against lives. This involves hard judgments.
1:25:18
Speaker 8: Those working under the conditions of greatest radiation risk. In
1:25:23
Speaker 8: atomic research, in industrial plants using isotopes and so on
1:25:28
Speaker 8: can be allowed to set relatively high limits for total
1:25:32
Speaker 8: radiation dosages and dose rates that they may absorb with
1:25:37
Speaker 8: time with reasonable safety, but such rates will never do
1:25:42
Speaker 8: for the population. Generally, a relative few can voluntarily endure
1:25:47
Speaker 8: risks both somatic and genetic, that we cannot sanely expect
1:25:52
Speaker 8: of mankind as a whole. From fruitfly experiments, it would
1:25:57
Speaker 8: seem that a total exposure of thirty to one hundred
1:26:01
Speaker 8: rads of radiation will double the spontaneous mutation rate. So
1:26:06
Speaker 8: much radiation and such a doubling of the rate would
1:26:09
Speaker 8: be considered intolerable for humanity. Some geneticists have recommended that
1:26:16
Speaker 8: the average total exposure of human beings in the first
1:26:19
Speaker 8: thirty years of life be set at ten rads. Note
1:26:24
Speaker 8: that this figure is set as a maximum. Every reasonable
1:26:28
Speaker 8: method it is expected will be used to allow mankind
1:26:32
Speaker 8: to fall as far short of this figure as possible.
1:26:36
Speaker 8: Note also that the ten red figure is an average maximum.
1:26:41
Speaker 8: The exposure of some individuals to a greater total dose
1:26:45
Speaker 8: would be viewed as tolerable for society if it were
1:26:49
Speaker 8: balanced by the exposure of other individuals to a lesser
1:26:53
Speaker 8: total dose. A total exposure of ten rads might increase
1:26:57
Speaker 8: the overall mutation rate is roughly estimated by ten percent.
1:27:03
Speaker 8: This is serious enough, but is bearable if we can
1:27:07
Speaker 8: convince ourselves that the alternative of abandoning radiation technology altogether
1:27:13
Speaker 8: will cause still greater suffering. A ten percent increase in
1:27:18
Speaker 8: mutation rate, whatever it might mean in personal suffering and
1:27:22
Speaker 8: public expense, is not likely to threaten the human race
1:27:26
Speaker 8: with extinction or even with serious degeneration. The human race
1:27:32
Speaker 8: as a whole may be thought of as somewhat analogous
1:27:35
Speaker 8: to a population of dividing cells in a growing tissue.
1:27:40
Speaker 8: Those affected by genetic damage drop out, and the slack
1:27:44
Speaker 8: is taken up by those not affected. If the number
1:27:47
Speaker 8: of those affected is increased, there would come a crucial
1:27:51
Speaker 8: point or threshold, where the slack would no longer be
1:27:55
Speaker 8: taken up. The genetic load might increase to a point
1:27:58
Speaker 8: where the species as as a whole would degenerate and
1:28:02
Speaker 8: fade toward extinction, a sort of racial radiation sickness. We
1:28:08
Speaker 8: are not near this threshold now, however, and can therefore
1:28:12
Speaker 8: as a species absorb a moderate increase in mutation rate
1:28:17
Speaker 8: without danger of extinction. On the other hand, it is
1:28:21
Speaker 8: not correct to argue, as some do, that an increase
1:28:25
Speaker 8: in mutation rate might be actually beneficial. The argument runs
1:28:31
Speaker 8: that a higher mutation rate might broaden the gene pool
1:28:35
Speaker 8: and make it more flexible, thus speeding up the course
1:28:38
Speaker 8: of evolution and hastening the advent of superman, brainier, stronger,
1:28:45
Speaker 8: healthier than we ourselves are. The truth seems to be
1:28:49
Speaker 8: that the gene pool as it exists now supplies us
1:28:53
Speaker 8: with all the variability we need for the effective working
1:28:57
Speaker 8: of the evolutionary Mechanismanism is functioning with such efficiency that
1:29:03
Speaker 8: broadening the gene pool cannot.
1:29:05
Speaker 9: Very well add to it.
1:29:06
Speaker 8: And if the hope of increased evolutionary efficiency were the
1:29:10
Speaker 8: only reason to tolerate man made radiation, it would be insufficient.
1:29:16
Speaker 8: The situation is rather analogous to that of a man
1:29:19
Speaker 8: who owns a good house that is heavily mortgaged. If
1:29:23
Speaker 8: he were offered a second house with a similar mortgage,
1:29:26
Speaker 8: he would have to refuse to be sure he would
1:29:30
Speaker 8: have twice the number of houses, But he would not
1:29:33
Speaker 8: need a second house, since he has all the comfort
1:29:35
Speaker 8: he can reasonably use in his first house, and he
1:29:39
Speaker 8: would not be able to.
1:29:40
Speaker 9: Afford a second mortgage.
1:29:43
Speaker 8: What humanity must do, if additional radiation damages absolutely necessary,
1:29:49
Speaker 8: is to take on as little of that added damage
1:29:52
Speaker 8: as possible, and not pretend that any direct benefits will
1:29:57
Speaker 8: be involved.
1:29:58
Speaker 9: Any pretense of that sort may well lure us.
1:30:01
Speaker 8: Into assuming still greater damage, damage we may not be
1:30:06
Speaker 8: able to afford, under any circumstances and for any reason. Actually,
1:30:13
Speaker 8: as the situation appears right now, it is not likely
1:30:16
Speaker 8: that the use of radiation in modern medicine, research, and
1:30:20
Speaker 8: industry will overstep the maximum bounds set by scientists who
1:30:26
Speaker 8: have weighed the problem carefully. Only nuclear warfare is likely
1:30:31
Speaker 8: to do so, and apparently those governments with large capacities
1:30:36
Speaker 8: in this direction are thoroughly aware of the danger, and
1:30:40
Speaker 8: so far at least have guided their foreign policies accordingly.
1:30:45
Speaker 9: End of section sixteen, end of
1:30:48
Speaker 8: The Genetic Effects of Radiation by Isaac Asimov and Theodosius
1:30:54
Speaker 8: Dobzansky