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Why Some People Are Gay · The Infographics Show Podcast

• 0:10
  Speaker 1: You know, usually when we talk about a medical diagnosis
• 0:13
  Speaker 1: or some kind of biological trait, there is this really
• 0:22
  Speaker 1: comforting expectation of precision. Oh totally, we crave that, right,
• 0:26
  Speaker 1: it feels like engineering. Yeah, I mean, you break your arm,
• 0:29
  Speaker 1: the X ray shows that jagged white line on the bone,
• 0:32
  Speaker 1: and the doctor just points to the illuminated screen and says,
• 0:35
  Speaker 1: there it is.
• 0:35
  Speaker 2: Yeah, that's the cause of your pain. Yeah, broken or
• 0:38
  Speaker 2: not broken exactly.
• 0:39
  Speaker 1: But then you step into the world of human behavior
• 0:43
  Speaker 1: and specifically neurodevelopment, and suddenly that X ray machine is
• 0:48
  Speaker 1: just utterly useless.
• 0:50
  Speaker 2: It's completely useless. You're looking at a biological landscape that
• 0:53
  Speaker 2: is well, incredibly murky, and that.
• 0:55
  Speaker 1: Is exactly where we are heading today. Welcome to be
• 0:58
  Speaker 1: on Infographics. I'm so glad you're joining it.
• 1:00
  Speaker 2: Yeah, it's great to have you here.
• 1:01
  Speaker 1: Our mission today is to step past those sensationalized headlines,
• 1:05
  Speaker 1: leap over the oversimplified pie charts, and uncover the really
• 1:10
  Speaker 1: intricate biological, genetic, and evolutionary mechanisms behind human sexual orientation.
• 1:15
  Speaker 2: Because the biology of attraction is honestly one of the
• 1:18
  Speaker 2: most compelling mysteries in human physiology.
• 1:22
  Speaker 3: It really is.
• 1:22
  Speaker 2: We are looking at genetics, hormones, brain structure, and even
• 1:27
  Speaker 2: the mother's immune system, all of it interacting in real
• 1:31
  Speaker 2: time before a person even takes their first breath.
• 1:33
  Speaker 1: Yeah, and I want to set the stage right out
• 1:35
  Speaker 1: of the gate here. What we are doing today isn't
• 1:37
  Speaker 1: just like reciting a textbook.
• 1:39
  Speaker 2: No, definitely not.
• 1:39
  Speaker 1: This is really a compilation of personal insights, fascinating data points,
• 1:44
  Speaker 1: and sheer scientific curiosities that we have gathered. Our central
• 1:48
  Speaker 1: theme today is moving entirely past that completely outdated nature
• 1:52
  Speaker 1: versus nurture.
• 1:53
  Speaker 2: Debate, right throwing out the idea of sexuality as a
• 1:56
  Speaker 2: simple choice exactly.
• 1:58
  Speaker 1: Instead, we are going to examine the incredibly complex cocktail
• 2:01
  Speaker 1: of biology that shapes who we are attracted to. And
• 2:05
  Speaker 1: before we jump in, a quick reminder, if you are
• 2:07
  Speaker 1: enjoying our explorations here on Beyond Infographics, please take a
• 2:11
  Speaker 1: second to rate the show five stars.
• 2:12
  Speaker 2: It takes two seconds and it really helps.
• 2:14
  Speaker 1: It really helps us keep bringing you these complex insights. So, okay,
• 2:18
  Speaker 1: let's unpack this. Before we can even look at the
• 2:21
  Speaker 1: biology of orientation, we really have to define what it
• 2:24
  Speaker 1: is we are actually trying to measure.
• 2:27
  Speaker 2: Yeah, because when we talked about orientation. The terminology constantly
• 2:31
  Speaker 2: gets tangled up in everyday conversation all the time. And
• 2:34
  Speaker 2: if our definitions are muddy, our scientific inquiry is going
• 2:37
  Speaker 2: to be muddy. People frequently conflate for very distinct concepts.
• 2:42
  Speaker 3: Okay, let's break those down, right.
• 2:43
  Speaker 2: So you have gender identity, gender expression, biological sex, and attraction.
• 2:49
  Speaker 2: Let's separate them. First, there is gender identity. This is
• 2:52
  Speaker 2: our core internal sense of.
• 2:54
  Speaker 3: Self, like the internal software.
• 2:56
  Speaker 2: Exactly, the internal software. It is how your brain understands
• 2:59
  Speaker 2: your whether that aligns with the sex you are assigned
• 3:02
  Speaker 2: at birth or if it differs or exists completely outside
• 3:06
  Speaker 2: the male female binary.
• 3:08
  Speaker 3: Right, and then the second one.
• 3:09
  Speaker 2: Then you have gender expression. This is the external communication
• 3:12
  Speaker 2: of gender.
• 3:12
  Speaker 3: So like how we show up in the world.
• 3:14
  Speaker 2: Yeah, it encompasses the clothing we choose, our hairstyles, our mannerisms,
• 3:19
  Speaker 2: even the pitch and cadence of our voice, and how
• 3:21
  Speaker 2: we interact socially.
• 3:23
  Speaker 3: Got it.
• 3:23
  Speaker 1: And the third is biological sex.
• 3:26
  Speaker 2: Yes, third is biological sex. This refers to the physical
• 3:31
  Speaker 2: physiological attributes your chromosomes, reproductive organs, visible genitalia, and your
• 3:37
  Speaker 2: ambient hormone levels. Okay, And the fourth, finally, The fourth
• 3:40
  Speaker 2: concept is attraction or sexual orientation. This is who we
• 3:44
  Speaker 2: feel drawn to sexually, romantically, or emotionally.
• 3:47
  Speaker 1: Right, and just to be crystal clear for everyone listening,
• 3:49
  Speaker 1: our focus today is purely on that fourth.
• 3:51
  Speaker 2: Pillar, attraction, purely attraction.
• 3:54
  Speaker 1: We are looking at the biology of who we are
• 3:56
  Speaker 1: drawn to. But historically, quantifying that attraction for scientific study
• 4:01
  Speaker 1: has been frankly a massive headache.
• 4:03
  Speaker 2: A total nightmare for researchers.
• 4:05
  Speaker 1: Yeah, because for a long time, the scientific community treated
• 4:08
  Speaker 1: attraction as a strict binary. You were either one hundred
• 4:12
  Speaker 1: percent heterosexual or one hundred percent homosexual.
• 4:14
  Speaker 2: There was basically no biological gray area recognized in the literature.
• 4:18
  Speaker 1: None, but that rigid binary held until what nineteen forty eight.
• 4:22
  Speaker 2: Exactly nineteen forty eight, when Alfred Kinsey published Sexual Behavior
• 4:25
  Speaker 2: in the Human Male. Kinsey introduced a zero to six
• 4:29
  Speaker 2: scale based on thousands of personal interviews. A zero represented
• 4:34
  Speaker 2: someone who is exclusively heterosexual, so having no physical or
• 4:39
  Speaker 2: psychological response to the same sex, okay, and a six
• 4:42
  Speaker 2: A six was exclusively homosexual, and then the numbers one
• 4:45
  Speaker 2: through five represented varying degrees of bisexual responses and experiences.
• 4:50
  Speaker 1: I've always found the Kinsey scale so fascinating because of
• 4:53
  Speaker 1: how disruptive it was for the late nineteen forty.
• 4:56
  Speaker 2: Oh, it was revolutionary.
• 4:57
  Speaker 1: It completely shattered that binary. It basically looked at humanity
• 5:01
  Speaker 1: and said, hey, a massive percentage of you are living
• 5:04
  Speaker 1: somewhere in the gray area.
• 5:05
  Speaker 2: Yeah, which people were not ready to hear.
• 5:07
  Speaker 3: No, But looking at.
• 5:09
  Speaker 1: The methodology, I've gathered that it wasn't perfect. I mean,
• 5:11
  Speaker 1: the famous research duo Masters in Johnson offered some pretty
• 5:15
  Speaker 1: heavy critiques of Kinsey's work, Right they did.
• 5:18
  Speaker 2: Their critiques targeted the oversimplification of lived experience.
• 5:21
  Speaker 3: What do you mean by that?
• 5:22
  Speaker 2: Well? Masters and Johnson pointed out that it is incredibly
• 5:25
  Speaker 2: difficult to assign a single static number to a human
• 5:29
  Speaker 2: being whose experiences evolve over time. Imagine an individual who
• 5:33
  Speaker 2: had exclusive same sex encounters in their twenties, but then, say,
• 5:38
  Speaker 2: married someone of the opposite sex and had a completely
• 5:41
  Speaker 2: different set of experiences in their forties.
• 5:43
  Speaker 3: Right, how do you average that out?
• 5:45
  Speaker 2: Exactly? How do you average a lifetime of complex psychological
• 5:49
  Speaker 2: and physical responses into a single digit? It basically forces
• 5:53
  Speaker 2: a dynamic moving target into a fixed position.
• 5:56
  Speaker 1: Which pushed researchers to develop a better map because the
• 5:59
  Speaker 1: Kinsey scale only really measured two dimensions, right, heterosexual and
• 6:02
  Speaker 1: homosexual experiences. So in nineteen seventy eight a researcher named
• 6:07
  Speaker 1: Fritz Klein developed the Klein's Sexual Orientation Grid or KSOG,
• 6:12
  Speaker 1: and that evaluates seven different dimensions.
• 6:14
  Speaker 2: Of sexuality, which is a huge step up. Yeah.
• 6:17
  Speaker 1: It looks at sexual attraction, sexual behavior, sexual fantasies, emotional preference,
• 6:21
  Speaker 1: social preference, self identification, and heterosexual or homosexual lifestyle.
• 6:26
  Speaker 2: And what makes Klein's grid far more scientifically robust is
• 6:31
  Speaker 2: that it doesn't just ask about these seven dimensions in
• 6:33
  Speaker 2: the present moment.
• 6:34
  Speaker 3: Right it looks at time.
• 6:35
  Speaker 2: It requires the subject to rate them based on the past,
• 6:39
  Speaker 2: the present, and what the person's ideal future would look like.
• 6:42
  Speaker 3: See.
• 6:42
  Speaker 1: I love the thoroughness of the grid, but I have
• 6:44
  Speaker 1: to push back a little here. Sure, far, even with
• 6:47
  Speaker 1: the seven dimension grid looking at the past, present, and future,
• 6:51
  Speaker 1: aren't we still trying to like pin a butterfly to
• 6:54
  Speaker 1: a board.
• 6:55
  Speaker 2: That's a good way to put it.
• 6:56
  Speaker 1: Because human experience is messy. Think about something like your
• 7:00
  Speaker 1: musical taste. My musical taste at age fifteen was wildly
• 7:05
  Speaker 1: different than it is now. Oh, totally and even now,
• 7:08
  Speaker 1: my responsiveness to a certain genre can change depending on
• 7:11
  Speaker 1: the situation, the venue, my mood, or who I'm with.
• 7:15
  Speaker 1: I've gathered from behavioral insights that sexuality can operate in
• 7:18
  Speaker 1: a similar way, like a concept known as sexual fluidity.
• 7:22
  Speaker 2: The music analogy is actually a perfect parallel for sexual fluidity.
• 7:27
  Speaker 2: Sexual responsiveness can change depending on the social environment, emotional intimacy,
• 7:31
  Speaker 2: and age.
• 7:32
  Speaker 3: Wait, there's data to back that up.
• 7:33
  Speaker 2: Oh yeah, Longitudinal studies tracking female sexuality over decades have
• 7:37
  Speaker 2: particularly noted this phenomenon. Yes, where attractions and behaviors exhibit
• 7:42
  Speaker 2: significant flexibility over a lifespan.
• 7:46
  Speaker 1: So if we acknowledge that attraction can be this fluid,
• 7:48
  Speaker 1: this multidimensional, evolving thing, how could it possibly be tied
• 7:53
  Speaker 1: to our fixed, rigid DNA.
• 7:56
  Speaker 2: Well, here's where it gets really interesting.
• 7:58
  Speaker 4: Yeah, because for decades there has been a relentless pursuit
• 8:02
  Speaker 4: to find the biological smoking gun for attraction, and usually
• 8:06
  Speaker 4: the finger points straight to genetics.
• 8:08
  Speaker 2: To understand the role of DNA, researchers rely heavily on
• 8:12
  Speaker 2: twins studies.
• 8:13
  Speaker 1: Right, the classic nature versus nurture.
• 8:15
  Speaker 2: Tests exactly identical or monozygotic twins occur When a single
• 8:20
  Speaker 2: fertilized egg splits into two, they share one hundred percent
• 8:23
  Speaker 2: of their genetic code.
• 8:24
  Speaker 3: Okay, And fraternal twins.
• 8:26
  Speaker 2: Eternal or dizzigotic twins occur when two separate eggs are
• 8:29
  Speaker 2: fertilized by two separate sperm. They share only about fifty
• 8:32
  Speaker 2: percent of their genes.
• 8:33
  Speaker 1: Just like any standard sibling pair.
• 8:35
  Speaker 2: Right. By comparing these two groups, scientists calculate concordance rates.
• 8:39
  Speaker 1: Meaning the probability that if one twin exhibits a trait,
• 8:43
  Speaker 1: the other twin will also exhibit it.
• 8:45
  Speaker 2: Yes, if a trait is entirely genetic, like your natural
• 8:49
  Speaker 2: eye color, identical twins will have a one hundred percent
• 8:52
  Speaker 2: concordance rate.
• 8:53
  Speaker 1: So what are the actual odds for sexual orientation?
• 8:57
  Speaker 2: In extensive analyzes of unbiased probability samples, if one identical
• 9:02
  Speaker 2: twin has a same sex attraction, the chance that the
• 9:05
  Speaker 2: other identical twin also shares that attraction sits around twenty
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  Speaker 2: four percent.
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  Speaker 1: Twenty four percent, okay, what about fraternal twins.
• 9:12
  Speaker 2: For fraternal twins, that number drops to about fifteen percent.
• 9:15
  Speaker 1: Okay, wow, So the jump from fifteen percent in fraternal
• 9:19
  Speaker 1: twins to twenty four percent in identical twins absolutely confirms
• 9:23
  Speaker 1: that genetics play a real, measurable role.
• 9:26
  Speaker 2: You can't ignore that statistical increase.
• 9:28
  Speaker 3: You really can't.
• 9:29
  Speaker 1: Right, But the identical twin rate is only twenty four percent.
• 9:33
  Speaker 1: That means seventy six percent of the time individuals with
• 9:36
  Speaker 1: the exact same genetic blueprint grow up to have different
• 9:39
  Speaker 1: sexual orientations.
• 9:40
  Speaker 2: Right.
• 9:40
  Speaker 1: That definitively proves that genes are not the only factor.
• 9:43
  Speaker 2: It shatters the concept of absolute genetic determinism. The blueprint
• 9:47
  Speaker 2: is not the building.
• 9:48
  Speaker 3: Ooh, I like that.
• 9:50
  Speaker 2: The DNA provides a foundation, but it does not dictate
• 9:53
  Speaker 2: the final architecture of attraction.
• 9:55
  Speaker 1: The media certainly didn't get that memo in the nineteen nineties.
• 9:57
  Speaker 2: Though, oh absolutely not.
• 9:59
  Speaker 1: The era of thin gay gene hype was everywhere. In
• 10:02
  Speaker 1: nineteen ninety three, a geneticist named Dean Hamer published a
• 10:06
  Speaker 1: famous linkage study.
• 10:07
  Speaker 2: Right, looking at family trees.
• 10:09
  Speaker 3: Yeah, he was.
• 10:10
  Speaker 1: Looking at the family trees of gay men, and he
• 10:12
  Speaker 1: noticed a distinct pattern. These men often had gay uncles
• 10:16
  Speaker 1: and gay cousins, but specifically on their mother's side of
• 10:20
  Speaker 1: the family.
• 10:21
  Speaker 2: And that maternal linkage immediately pointed researchers toward the.
• 10:24
  Speaker 1: X chromosome because biological males inherit an X chromosome from
• 10:29
  Speaker 1: their mothers and a Y from their fathers exactly.
• 10:32
  Speaker 2: Hamber's team mapped the X chromosomes of gay brothers and
• 10:35
  Speaker 2: found a statistical correlation at a very specific marker called
• 10:39
  Speaker 2: XQ twenty eight.
• 10:40
  Speaker 3: X Q twenty eight.
• 10:41
  Speaker 2: A significant number of the gay brothers shared this exact
• 10:44
  Speaker 2: genetic snippet at the tip of the X chromosome, and.
• 10:47
  Speaker 1: Man the headlines were relentless. Scientists discovered the gay gene.
• 10:51
  Speaker 1: It was on the cover of major magazines.
• 10:53
  Speaker 2: It implied there was a single, easily identifiable switch in.
• 10:56
  Speaker 3: Our DNA, right, But it didn't hold up, did it No.
• 11:00
  Speaker 2: Subsequent studies struggled immensely to replicate Hammer's findings with the
• 11:03
  Speaker 2: same level of statistical significance. Oh interesting. While later meta
• 11:08
  Speaker 2: analysis suggested there might be some minor linkage at XQ
• 11:11
  Speaker 2: twenty eight, the scientific consensus became abundantly clear that a
• 11:15
  Speaker 2: single solitary gay gene simply does not exist.
• 11:19
  Speaker 1: Plus, our technology has evolved so drastically since then. I mean,
• 11:22
  Speaker 1: the tools they use in the nineteen nineties are like
• 11:24
  Speaker 1: magnifying glasses compared to the Hubble telescope of modern genomics.
• 11:28
  Speaker 2: That is a great analogy.
• 11:30
  Speaker 1: Let's look at the Massive Genome Wide Association's study or
• 11:33
  Speaker 1: GWA from twenty nineteen.
• 11:35
  Speaker 2: The twenty nineteen gdo ways fundamentally transformed the field's understanding.
• 11:39
  Speaker 2: The scale was unprecedented.
• 11:41
  Speaker 1: They analyzed the DNA of over four hundred ninety thousand
• 11:44
  Speaker 1: people right aggregating data from the UK Biobank and twenty
• 11:47
  Speaker 1: three n.
• 11:48
  Speaker 2: ME almost half a million genomes.
• 11:50
  Speaker 1: To help visualize how GDOAS operates, I like to imagine
• 11:53
  Speaker 1: human DNA as seven billion copies of the exact same encyclopedia.
• 11:57
  Speaker 2: Okay, I see whe you're going with this.
• 11:59
  Speaker 1: We all have the same basic chapters, paragraphs, and sentences.
• 12:03
  Speaker 1: What scientists do in a GOOA is run a massive
• 12:07
  Speaker 1: computational scan through hundreds of thousands of those encyclopedias, looking
• 12:11
  Speaker 1: for single letter typos in the text that show up
• 12:14
  Speaker 1: slightly more often in people who exhibit a certain trait.
• 12:17
  Speaker 2: Those typos are called single nucleotide polymorphisms, or SNPs. They
• 12:23
  Speaker 2: are microscopic variations in the DNA sequence. When the researchers
• 12:27
  Speaker 2: scanned those half a million genomes looking for smps, correlated
• 12:31
  Speaker 2: with same sex behavior. They found hundreds, possibly thousands of
• 12:35
  Speaker 2: tiny genetic variants spread all across the genome, not just
• 12:40
  Speaker 2: on the X chromosome, not just on the X chromosome,
• 12:42
  Speaker 2: but everywhere.
• 12:42
  Speaker 1: But here is the critical part. Even when you run
• 12:45
  Speaker 1: the advanced statistical models and add up the influence of
• 12:48
  Speaker 1: all those thousands of variants together, they only account for
• 12:51
  Speaker 1: about eight to twenty five percent of the variation and
• 12:54
  Speaker 1: sexual behavior.
• 12:55
  Speaker 2: So genetics is a factor, but it's polygenic, meaning many
• 12:58
  Speaker 2: genes working in concert.
• 13:00
  Speaker 1: And even then it's a minority shareholder in the company
• 13:02
  Speaker 1: of our attraction exactly.
• 13:04
  Speaker 2: But what is particularly fascinating about the specific genetic variants
• 13:08
  Speaker 2: they uncovered in that twenty nineteen study is how those
• 13:11
  Speaker 2: genes multitask, multitask how in biology we call this pleotropy.
• 13:15
  Speaker 3: Oh, the overlaps are wild.
• 13:17
  Speaker 1: They found specific variants on chromosomes eleven and fifteen in
• 13:21
  Speaker 1: men that correlated with same sex behavior. But those exact
• 13:24
  Speaker 1: same genetic markers are simultaneously involved in biological pathways that
• 13:28
  Speaker 1: seem completely unrelated, like what well, For instance, the variant
• 13:32
  Speaker 1: on chromosome eleven has strong ties to a faction our
• 13:35
  Speaker 1: sense of smell.
• 13:36
  Speaker 2: The connection to olfaction is incredibly intriguing. Human mating and
• 13:40
  Speaker 2: attraction operate heavily on subconscious olfactory cues likex pheromones. Right,
• 13:45
  Speaker 2: we are constantly processing pheromones and the scent of major
• 13:49
  Speaker 2: histocompatibility complexes to determine genetic compatibility with a potential partner.
• 13:54
  Speaker 3: Oh wow.
• 13:54
  Speaker 2: The fact that genes influencing sexual orientation are physically linked
• 13:58
  Speaker 2: to the genes constructing our olfactory receptors suggests a deep
• 14:01
  Speaker 2: evolutionary intersection between how we perceive scent and who we
• 14:05
  Speaker 2: are drawn to.
• 14:06
  Speaker 3: That makes so much sense.
• 14:07
  Speaker 1: And then the variant on chromosome fifteen is linked to
• 14:10
  Speaker 1: male pattern baldness.
• 14:11
  Speaker 2: Baldness?
• 14:12
  Speaker 3: Yeah, what is.
• 14:13
  Speaker 1: The evolutionary mechanism connecting romantic attraction to losing your hair?
• 14:17
  Speaker 1: They also found genetic overlaps with personality traits like openness
• 14:21
  Speaker 1: to experience and risk taking.
• 14:23
  Speaker 2: It illustrates how interconnected human genetics really is. You don't
• 14:26
  Speaker 2: have one gene for one trait, You have vast network
• 14:29
  Speaker 2: of genes influencing dozens of traits simultaneously.
• 14:33
  Speaker 1: We must apply a rigorous critical lens here, however, absolutely
• 14:36
  Speaker 1: as massive as that twenty nineteen study was, it suffers
• 14:39
  Speaker 1: from a glaring systemic flaw prevalent in modern genomics. The
• 14:43
  Speaker 1: DITA pool was overwhelmingly focused on individuals of European, specifically
• 14:48
  Speaker 1: Caucasian ancestry.
• 14:49
  Speaker 2: Ah yes diversity issue.
• 14:52
  Speaker 1: By essentially excluding genetic data from populations across Africa, Asia,
• 14:56
  Speaker 1: and Latin America, researchers are left with a massive blind spot.
• 15:00
  Speaker 1: We are attempting to draw definitive biological conclusions about all
• 15:03
  Speaker 1: of humanity based on a very narrow genetic subset of humanity.
• 15:07
  Speaker 2: A phenomenal point and a great reminder that science is
• 15:10
  Speaker 2: an ongoing, cautious process of refinement.
• 15:12
  Speaker 1: So if DNA only accounts for at most a quarter
• 15:16
  Speaker 1: of the puzzle, where does the other seventy five percent originate?
• 15:20
  Speaker 1: If it's not the genetic code itself, what else is
• 15:23
  Speaker 1: shaping human neurodevelopment before we are even born?
• 15:26
  Speaker 2: We have to travel back to the hormonal crucible of
• 15:28
  Speaker 2: the womb. The womb environment the prenatal environment is currently
• 15:32
  Speaker 2: the most heavily supported biological hypothesis in the field of
• 15:35
  Speaker 2: sexual orientation. It begins with a fundamental developmental reality. All
• 15:41
  Speaker 2: fetal brains, regardless of their chromosomal sex, start out in
• 15:44
  Speaker 2: a default female typical state.
• 15:47
  Speaker 1: Wait, really, the default human template is female.
• 15:49
  Speaker 2: Yes. The developmental divergence only initiates if the fetus possesses
• 15:53
  Speaker 2: a Y chromosome.
• 15:54
  Speaker 1: Ok.
• 15:55
  Speaker 2: On that Y chromosome resides the SRY gene. Around the
• 15:58
  Speaker 2: twelve week of gestation, the SAY gene activates, triggering the
• 16:02
  Speaker 2: undifferentiated gonads to develop into testes.
• 16:05
  Speaker 3: Okay, so week twelve is the big moment right.
• 16:07
  Speaker 2: Once those tiny field tests form, they immediately begin synthesizing
• 16:10
  Speaker 2: and secreting massive amounts of testosterone.
• 16:12
  Speaker 1: So the fetal brain is essentially subjected to a testosterone wash.
• 16:16
  Speaker 2: Exactly when that wave of testosterone hits the fetal cells,
• 16:20
  Speaker 2: it travels straight to the developing neural structures. It acts
• 16:23
  Speaker 2: on specific hormone receptors in the brain, essentially organizing and
• 16:28
  Speaker 2: masculinizing the neural.
• 16:29
  Speaker 3: Circuits, and that sets up future behaviors.
• 16:32
  Speaker 2: This prenatal organization lays the groundwork for typical male behaviors
• 16:36
  Speaker 2: that will emerge decades later, including sexual attraction to females.
• 16:39
  Speaker 3: And if the brain doesn't get.
• 16:40
  Speaker 2: That wash, if the brain does not receive that testosterone wash,
• 16:44
  Speaker 2: or if the neural receptors fail to process. It typically
• 16:48
  Speaker 2: the brain remains in its default female typical organization, which
• 16:52
  Speaker 2: directs future attraction toward males.
• 16:54
  Speaker 1: It's mind blowing. We are talking about microscopic chemical events
• 16:58
  Speaker 1: happening at twelve weeks of justtingtion that dictate romantic attractions
• 17:02
  Speaker 1: twenty years later.
• 17:03
  Speaker 2: It really is incredible, and we.
• 17:04
  Speaker 1: Actually have physical biological markers that we can see with
• 17:07
  Speaker 1: our naked eyes that hint at this prenatal hormone exposure.
• 17:11
  Speaker 3: One of the most.
• 17:11
  Speaker 1: Robust physical markers is the two D point four D
• 17:14
  Speaker 1: digit ratio.
• 17:15
  Speaker 2: Yes, the finger ratio. For everyone listening. If you look
• 17:19
  Speaker 2: at your right hand, the two D point four D
• 17:22
  Speaker 2: ratio compares the length of your index finger the second digit,
• 17:26
  Speaker 2: to the length of your ring finger the fourth digit.
• 17:28
  Speaker 3: Okay, everyone looking at their hands right now.
• 17:30
  Speaker 2: Orthopedic and endocrinological research has consistently demonstrated that the growth
• 17:35
  Speaker 2: plates in these specific fingers are highly sensitive to the
• 17:39
  Speaker 2: balance of testosterone and estrogen in the womb.
• 17:42
  Speaker 1: Oh I see so, Heterosexual women generally tend to have
• 17:45
  Speaker 1: index and ring fingers that are roughly the same length.
• 17:48
  Speaker 1: Heterosexual men typically have a ring finger that is noticeably
• 17:51
  Speaker 1: longer than their index finger.
• 17:52
  Speaker 2: Right, which is considered a more masculine ratio, indicating higher
• 17:56
  Speaker 2: prenatal testosterone exposure.
• 17:58
  Speaker 1: But when researchers examine the hands of life lesbians, they
• 18:00
  Speaker 1: find that on average, their digit ratio shifts toward that
• 18:03
  Speaker 1: masculine pattern. Their ring fingers tend to be longer, suggesting
• 18:06
  Speaker 1: they were exposed to higher levels of testosterone in utero
• 18:09
  Speaker 1: compared to heterosexual women.
• 18:11
  Speaker 2: It basically acts as a permanent fossil record of your
• 18:14
  Speaker 2: time in the.
• 18:14
  Speaker 3: Wormb that is wild.
• 18:17
  Speaker 2: We see the profound impact of prenatal hormones even more
• 18:20
  Speaker 2: clearly when we examine specific medical conditions such as congenital
• 18:24
  Speaker 2: adrenal hyperplasia or CAAH right.
• 18:27
  Speaker 1: CACH is a genetic condition where a fetus's adrenal glands
• 18:31
  Speaker 1: lack a specific enzyme required to produce cortisol. Exactly because
• 18:35
  Speaker 1: the body isn't producing cortisol, the brain sends continuous signals
• 18:39
  Speaker 1: to the adrenal glands to work harder. This overdrive causes
• 18:43
  Speaker 1: the adrenal glands to overproduce androgens, which are male sex
• 18:46
  Speaker 1: hormones like testosterone, so.
• 18:48
  Speaker 2: The environment changes completely.
• 18:49
  Speaker 1: Yeah When a biologically female fetus with XX chromosomes has CAAH,
• 18:54
  Speaker 1: her developing brain is exposed to unusually high levels of
• 18:57
  Speaker 1: testosterone before birth, and.
• 18:59
  Speaker 2: The clinical outcomes in adulthood providing incredibly clear evidence of
• 19:03
  Speaker 2: the power of the prenatal hormonal environment.
• 19:05
  Speaker 3: What kind of outcomes?
• 19:06
  Speaker 2: When researchers conduct longitudinal follow ups with adult women who
• 19:10
  Speaker 2: have CAAH, they document significant shifts in their sexuality.
• 19:14
  Speaker 1: Wow. Studies show that up to thirty eight percent of
• 19:16
  Speaker 1: women with CAACH report by sexual attraction or a lack
• 19:20
  Speaker 1: of exclusive heterosexual interest.
• 19:22
  Speaker 2: Right. Yes, that is a massively higher rate than the
• 19:26
  Speaker 2: general female population. They also exhibit significantly higher rates of
• 19:31
  Speaker 2: childhood gender nonconformity, like a strong preference for rough and
• 19:35
  Speaker 2: tumble play or typical boys toys.
• 19:37
  Speaker 1: It is a direct observable chain of causality from an
• 19:41
  Speaker 1: adrenal gland mutation to a hormone wash in the womb
• 19:45
  Speaker 1: to sexual orientation decades later.
• 19:48
  Speaker 2: But this brings up a massive contradiction, however, a real
• 19:52
  Speaker 2: puzzle for researchers.
• 19:53
  Speaker 3: Oh, what's a contradiction.
• 19:55
  Speaker 2: Let's return to the identical twins. They share one hundred
• 19:59
  Speaker 2: percent of their DNA and they share the exact same
• 20:01
  Speaker 2: womb environment at the exact same time. They're bathed in
• 20:04
  Speaker 2: the same maternal hormone. Oh oh right, Yet seventy six
• 20:08
  Speaker 2: percent of the time, if one is gay, the other
• 20:09
  Speaker 2: is straight. How is that physically possible? If genetics and
• 20:12
  Speaker 2: the shared prenatal hormonal wash are the deciding factors.
• 20:16
  Speaker 1: I was wrestling with this. It's like having two identical
• 20:19
  Speaker 1: computers running off the exact same hard drive, plugged into
• 20:21
  Speaker 1: the exact same power source, but when you boot them up,
• 20:24
  Speaker 1: they displayed different operating systems.
• 20:26
  Speaker 2: That's a brilliant way to phrase it.
• 20:27
  Speaker 3: How do you explain the divergence?
• 20:29
  Speaker 2: The answer likely resides in the field of epigenetics, specifically
• 20:33
  Speaker 2: an epigenetic model proposed by evolutionary geneticist William Rice. Epigenetics, Okay,
• 20:39
  Speaker 2: your DNA is the hardware, but epigenetics is the software.
• 20:42
  Speaker 2: Epigenetics involves temporary chemical switches, often called epi marks, which
• 20:47
  Speaker 2: are essentially methyl groups that attach to your DNA.
• 20:50
  Speaker 1: So what do these methyl groups actually do?
• 20:52
  Speaker 2: They physically block transcription proteins from reading the gene. They
• 20:57
  Speaker 2: act like a volume knob, turning the expression of certain
• 20:59
  Speaker 2: genes up or down.
• 21:00
  Speaker 3: Okay, volume knob.
• 21:02
  Speaker 2: Rice's model suggests that these specific epimarks control how sensitive
• 21:06
  Speaker 2: the developing fetal brain is to testosterone. A male fetus
• 21:10
  Speaker 2: develops epimarks that protect it from being undermasculinized if the
• 21:14
  Speaker 2: mother's testosterone levels suddenly dip.
• 21:16
  Speaker 3: And a female fetus.
• 21:17
  Speaker 2: A female fetus develops epimrks that protect her from being
• 21:20
  Speaker 2: overmasculinized if maternal testosterone spikes. Normally, these marks are supposed
• 21:25
  Speaker 2: to be erased and reset between generations.
• 21:27
  Speaker 1: But occasionally the software fails to reboot properly exactly.
• 21:32
  Speaker 2: Sometimes these protective epimarks survive the erasure process. They are
• 21:36
  Speaker 2: passed down intact from a father to a daughter or
• 21:39
  Speaker 2: mother to a son.
• 21:40
  Speaker 3: Oh Wow.
• 21:41
  Speaker 2: A male fetus might inherit an epimark that dials down
• 21:44
  Speaker 2: his brain sensitivity to the testosterone his own tests are producing.
• 21:49
  Speaker 2: Even though the hormone is physically present in the womb,
• 21:51
  Speaker 2: his brain receptors are chemically blocked from registering it fully.
• 21:55
  Speaker 1: Which means his neural circuits for sexual attraction remain in
• 21:59
  Speaker 1: the default female typical state. Yes, so, even though the
• 22:03
  Speaker 1: identical twins are floating in the exact same hormonal bath,
• 22:06
  Speaker 1: they might have subtly different epigenetic software running one twins'
• 22:10
  Speaker 1: brain absorbs the testosterone, and the other twins' brain is
• 22:14
  Speaker 1: epigenetically shielded from it precisely. You know, whenever we talk
• 22:18
  Speaker 1: about biology shaping human behavior, there is always the lingering
• 22:21
  Speaker 1: growth of the nurture argument, the socialization theory, right, the
• 22:25
  Speaker 1: idea that maybe it's not the womb, maybe it's how
• 22:27
  Speaker 1: you raise the society you live in, the socialization you
• 22:30
  Speaker 1: receive as a child.
• 22:31
  Speaker 2: But there is a very dark, deeply tragic chapter in
• 22:35
  Speaker 2: medical history that forcefully closes the door on the idea
• 22:39
  Speaker 2: that sexual orientation is just a product of socialization.
• 22:42
  Speaker 1: The surgical reassignment cases of the mid twentieth century.
• 22:46
  Speaker 2: It is a highly sensitive topic, particularly the famous case
• 22:48
  Speaker 2: of David Reimer, but scientifically it provides irrefutable data regarding
• 22:53
  Speaker 2: early brain organization.
• 22:55
  Speaker 1: Let me contextualize this because between the nineteen sixties and
• 22:58
  Speaker 1: two thousand, under the influence of psychologists like John Money,
• 23:06
  Speaker 1: there was a prevailing medical theory that children were essentially
• 23:09
  Speaker 1: born as psychosexual blank slates.
• 23:11
  Speaker 2: Right.
• 23:12
  Speaker 1: The theory aggressively asserted that gender identity and sexual orientation
• 23:15
  Speaker 1: were entirely learned constructs. Consequently, when infant boys suffered catastrophic
• 23:20
  Speaker 1: accidents like botched circumcisions or were born with severe penile defects,
• 23:25
  Speaker 1: doctors recommended surgically reassigning them to be female.
• 23:28
  Speaker 2: The infants were surgically castrated, provided with female genitalia, and
• 23:32
  Speaker 2: their parents were strictly instructed to raise them as girls.
• 23:35
  Speaker 2: Just horrifying, they were heavily socialized with traditional female clothing, toys,
• 23:40
  Speaker 2: and pronouns, and the medical establishment insisted the parents never
• 23:44
  Speaker 2: reveal the truth about their biological birth sex.
• 23:47
  Speaker 1: So, if the nurture theory was correct, if sexual orientation
• 23:51
  Speaker 1: is just a product of how you are raised and
• 23:53
  Speaker 1: what clothes you wear, these children should have grown up
• 23:56
  Speaker 1: to be women who were attracted to men. They should
• 23:58
  Speaker 1: have DA shows the exact opposite. Despite being heavily socialized
• 24:03
  Speaker 1: as females with absolutely no knowledge of their biological truth,
• 24:07
  Speaker 1: these individuals almost universally grew up to be strongly attracted
• 24:11
  Speaker 1: to women.
• 24:11
  Speaker 2: Their sexual orientation tracks strictly with their biological sex and
• 24:14
  Speaker 2: their pre naval brain organization, completely overriding years of intense,
• 24:19
  Speaker 2: deliberate and pervasive social conditioning.
• 24:22
  Speaker 1: You cannot socialize a biologically male organized brain to be
• 24:26
  Speaker 1: attracted to men just by treating them like a girl.
• 24:28
  Speaker 1: The neurological hardwiring is laid down before birth. We've established
• 24:32
  Speaker 1: that the fetal brain is incredibly sensitive to the mother's
• 24:35
  Speaker 1: hormonal environment, but hormones aren't the only biological agents circulating
• 24:40
  Speaker 1: in that shared bloodstream. We also have to consider her
• 24:43
  Speaker 1: immune system, which leads to one of the most reliable
• 24:47
  Speaker 1: and bizarre statistics in this entire field.
• 24:49
  Speaker 2: Oh, the fraternal birth order effect.
• 24:51
  Speaker 1: The statistic is just staggering to me. For every older
• 24:54
  Speaker 1: biological brother, a man has his odds of being gay
• 24:58
  Speaker 1: increased by thirty three percent.
• 25:00
  Speaker 2: Let's clarify the exact parameters of this finding, though, because
• 25:03
  Speaker 2: they are incredibly specific.
• 25:05
  Speaker 3: Okay, what are the caveats?
• 25:07
  Speaker 2: It only applies to right handed men. The statistical effect
• 25:10
  Speaker 2: vanishes in left handed men, a neurological quirk we still
• 25:13
  Speaker 2: don't fully understand.
• 25:15
  Speaker 3: Wait, really, left handed men are exempt.
• 25:17
  Speaker 2: Yes, And crucially, it only applies to biological brothers who
• 25:21
  Speaker 2: just stated in the same mother's wombs.
• 25:23
  Speaker 1: So if a boy is adopted into a family with
• 25:26
  Speaker 1: five older boys, his odds do not increase. It has
• 25:29
  Speaker 1: absolutely nothing to do with the social environment of growing
• 25:32
  Speaker 1: up around older brothers exactly.
• 25:34
  Speaker 2: It is strictly a biological phenomenon occurring inside the womb.
• 25:38
  Speaker 1: What is the biological mechanism proposed for this?
• 25:40
  Speaker 2: The leading theory is the maternal immune hypothesis.
• 25:44
  Speaker 1: Okay, explain the immunology of this. How does a mother's
• 25:47
  Speaker 1: body react to her own baby.
• 25:50
  Speaker 2: Remember that the mother is biologically female, right, her cells
• 25:54
  Speaker 2: only possess X chromosomes. A male fetus has a Y chromosome.
• 25:58
  Speaker 2: As the male feet is developed, that Y chromosome directs
• 26:02
  Speaker 2: the production of highly specific proteins such as the nognfull
• 26:05
  Speaker 2: y in hy antigens antigens. These proteins are vital for
• 26:09
  Speaker 2: building the male body and masculinizing the fetal brain. But
• 26:13
  Speaker 2: because the mother's immune system has never encountered these male
• 26:15
  Speaker 2: specific proteins in her own body, it registers them as
• 26:18
  Speaker 2: foreign invaders.
• 26:19
  Speaker 3: WHOA.
• 26:20
  Speaker 1: It's treating the baby's proteins the same way it would
• 26:22
  Speaker 1: treat a virus or a bacterial infection.
• 26:25
  Speaker 2: During a first male pregnancy, the mother's immune system detects
• 26:29
  Speaker 2: these Y proteins and slowly begins activating B cells to
• 26:32
  Speaker 2: create targeted antibodies against them.
• 26:33
  Speaker 3: But the first baby is fine.
• 26:35
  Speaker 2: Yes, by the time the immune system has manufactured a
• 26:38
  Speaker 2: sufficient army of antibodies. The first sun is usually already born. However,
• 26:43
  Speaker 2: the human immune system possesses long term.
• 26:46
  Speaker 3: Memory AH like a vaccine response.
• 26:48
  Speaker 2: With each successive male pregnancy, her immune system recognizes those
• 26:52
  Speaker 2: y proteins immediately and produces antibodies much faster and in
• 26:56
  Speaker 2: significantly higher quantities, and.
• 26:58
  Speaker 1: These maternal antibiododies physically travel into the baby's body.
• 27:02
  Speaker 2: Yes, the placenta is designed to transport maternal antibodies to
• 27:06
  Speaker 2: the fetus to provide passive immunity against diseases. Specialized receptors
• 27:11
  Speaker 2: on the placenta grab these IgG antibodies and pull them
• 27:15
  Speaker 2: across the placental barrier into the fetal bloodstream.
• 27:17
  Speaker 3: So the antibodies get in.
• 27:19
  Speaker 2: The theory suggests these anti male antibodies cross into the
• 27:22
  Speaker 2: fetal brain with a bind to the NLG and four
• 27:25
  Speaker 2: YE proteins, essentially neutralizing them.
• 27:27
  Speaker 1: So by neutralizing those proteins, the antibodies prevent them from
• 27:31
  Speaker 1: executing their job of masculinizing the neural circuits that direct
• 27:34
  Speaker 1: sexual attraction.
• 27:35
  Speaker 2: The brain remains in its default female typical orientation.
• 27:39
  Speaker 1: The more older brothers you have, the higher the mother's
• 27:42
  Speaker 1: antibody count, and the higher the statistical odds of that
• 27:45
  Speaker 1: neural masculinization being interrupted.
• 27:47
  Speaker 2: That is the hypothesis.
• 27:48
  Speaker 1: Yes, I want to push back on this though, Let's
• 27:51
  Speaker 1: play Devil's advocate. This sounds like a neat, tidy explanation
• 27:55
  Speaker 1: with a bow on top, but it clearly doesn't explain
• 27:58
  Speaker 1: the entirety of human sexuality.
• 28:00
  Speaker 2: It absolutely does not, and we have to examine the
• 28:02
  Speaker 2: limitations of this data. While the fraternal birth order effect
• 28:06
  Speaker 2: is statistically robust, epidemiological estimates suggest it only accounts for
• 28:12
  Speaker 2: about fifteen to twenty nine percent of gay men.
• 28:15
  Speaker 1: Exactly, what about firstborn gay men? What about gay men
• 28:18
  Speaker 1: who only have older sisters. Furthermore, researchers have found zero
• 28:22
  Speaker 1: evidence of an equivalent older sister effect for lesbians. The
• 28:25
  Speaker 1: maternal immune hypothesis appears strictly limited to the gestational mechanics
• 28:30
  Speaker 1: of male fetuses.
• 28:31
  Speaker 2: There's also the issue of how science gets published.
• 28:33
  Speaker 3: Oh publication bias.
• 28:35
  Speaker 2: Yes, the publication bias problem. Researcher J. Michael Bailey is
• 28:38
  Speaker 2: frequently cautioned that the scientific publishing industry is highly incentivized
• 28:43
  Speaker 2: to highlight surprising findings, and.
• 28:45
  Speaker 1: A thirty three percent increase per older brother is highly surprising.
• 28:50
  Speaker 2: It generates headlines, it secures grant funding, and it boosts
• 28:53
  Speaker 2: academic careers. While the data itself stands up to rigorous
• 28:57
  Speaker 2: peer review, we must remain scared optical of how much
• 29:00
  Speaker 2: weight we assign to it. It is merely one biological
• 29:04
  Speaker 2: mechanism in a sea of unknown variables.
• 29:06
  Speaker 1: It's a massive, cautious mosaic. Hey, quick reminder, if you
• 29:11
  Speaker 1: are finding this exploration as fascinating as we are, take
• 29:14
  Speaker 1: a second to tap that five star rating on your
• 29:16
  Speaker 1: podcast app. It genuinely supports our work on beyond infographics.
• 29:19
  Speaker 2: Yes, thank you so much for that.
• 29:21
  Speaker 3: Okay, let's keep going.
• 29:22
  Speaker 1: We've talked about genetics, testosterone washes, epigenetic software glitches, and
• 29:26
  Speaker 1: maternal antibodies neutralizing proteins. All of these mechanisms are purportedly
• 29:31
  Speaker 1: altering the physical structure of the fetal brain.
• 29:33
  Speaker 2: Yes, the physical structure.
• 29:35
  Speaker 1: If these maternal antibodies are actively neutralizing masculinizing proteins in
• 29:39
  Speaker 1: the fetal brain, we shouldn't just be seeing behavioral changes
• 29:42
  Speaker 1: decades later. We should be able to look inside the
• 29:44
  Speaker 1: adult brain and see the physical scars of that interrupted development.
• 29:49
  Speaker 3: Are there?
• 29:49
  Speaker 1: Physical anatomical differences we can point to.
• 29:52
  Speaker 2: We have to delve into neuroanatomy for that. Specifically, the
• 29:55
  Speaker 2: landmark research conducted by Simon LeVay in the early nineteen nineties.
• 29:59
  Speaker 2: Okay Leve LaVey was a neurobiologist who decided to investigate
• 30:02
  Speaker 2: the hypothalamus.
• 30:04
  Speaker 1: Now, the hypothalamus is situated deep in the brain. It's
• 30:07
  Speaker 1: essentially the command center for the endocrine system, regulating fundamental
• 30:10
  Speaker 1: primal drives like temperature, hunger, and sexual behavior exactly.
• 30:15
  Speaker 2: LaVey focused his attention on a microscopic cluster of neurons
• 30:18
  Speaker 2: within the hypothalmus called the third interstitial nucleus of the
• 30:23
  Speaker 2: anterior hypothalamus or IONA.
• 30:25
  Speaker 3: Three NAH three got it.
• 30:27
  Speaker 2: In animal models, the equivalent of this neural region is
• 30:30
  Speaker 2: demonstrably responsible for directing typical male sexual behavior, like mounting
• 30:35
  Speaker 2: an attraction to females. Because brain imaging technology in the
• 30:39
  Speaker 2: nineteen nineties lacked the resolution to measure a structure of
• 30:42
  Speaker 2: this tiny and living patients, LaVey had to perform post
• 30:45
  Speaker 2: mortem dissections.
• 30:46
  Speaker 1: He manually measured these neuron clusters and deceased individuals.
• 30:50
  Speaker 2: He discovered that the INH three region in heterosexual men
• 30:53
  Speaker 2: was more than twice the size of the IONH three
• 30:56
  Speaker 2: region in homosexual.
• 30:57
  Speaker 3: Men, twice the sith.
• 30:58
  Speaker 2: Yes, the neural cluster in the gay man was significantly
• 31:02
  Speaker 2: smaller structurally, resembling the size typically found in heterosexual women.
• 31:07
  Speaker 1: So a physically feminized brain structure. But wait, I remember
• 31:10
  Speaker 1: reading the history of the study and there was a
• 31:12
  Speaker 1: massive confounding variable that critics instantly attacked.
• 31:15
  Speaker 2: Uh. Yes, the HIV AIDS epidemic.
• 31:18
  Speaker 1: Right, it was the early nineteen nineties and the epidemic
• 31:21
  Speaker 1: was devastating the gay community. Didn't the vast majority of
• 31:25
  Speaker 1: LaVey's gay subjects die of AIDS related complications.
• 31:28
  Speaker 2: They did. Critics rightfully pointed out that the HIV virus
• 31:32
  Speaker 2: itself or the toxic anti retroviral medications used at the time,
• 31:36
  Speaker 2: might have caused the neurodegeneration that shrank that part of
• 31:39
  Speaker 2: the brain.
• 31:39
  Speaker 1: They argued, it was a symptom of a terminal illness,
• 31:42
  Speaker 1: not a natural anatomical difference link to sexual orientation.
• 31:45
  Speaker 2: How did Levey defend his findings against that critique?
• 31:48
  Speaker 3: Wait, didn't he have a specific control group?
• 31:51
  Speaker 2: He did? He anticipated the variable. His control group of
• 31:54
  Speaker 2: heterosexual men intentionally included individuals who had contracted HIV through
• 31:59
  Speaker 2: intravenous drug use or blood transfusions and had subsequently died
• 32:02
  Speaker 2: of AIDS.
• 32:03
  Speaker 3: Oh, that's smart.
• 32:04
  Speaker 2: When he dissected their brains, the straight men who died
• 32:07
  Speaker 2: of AIDS did not exhibit a shrunken h three. Their
• 32:11
  Speaker 2: neuron clusters retained the typical larger male volume. This effectively
• 32:15
  Speaker 2: proved that the disease process was not responsible for the
• 32:17
  Speaker 2: structural difference.
• 32:19
  Speaker 3: That is meticulous scientific control.
• 32:21
  Speaker 1: What really solidifies this anatomical argument for me is that
• 32:24
  Speaker 1: we observe the exact same phenomenon occurring naturally in the
• 32:28
  Speaker 1: animal kingdom, specifically in domestic sheep.
• 32:32
  Speaker 2: The ovine model provides an incredible biological parallel.
• 32:35
  Speaker 1: Apparently, six to eight percent of domestic rams are exclusively
• 32:38
  Speaker 1: attracted to other rams. They display zero mating interest.
• 32:41
  Speaker 3: In the use.
• 32:42
  Speaker 2: Yes, it's quite well documented.
• 32:44
  Speaker 1: When veterinary researchers perform autopsies on these homosexual rams, they
• 32:49
  Speaker 1: examine the ovine equivalent of the NAH three, a brain
• 32:52
  Speaker 1: region called the oSDN. The results mirror levase human studies perfectly.
• 32:57
  Speaker 2: The brain region in the gay rams is significantly smaller.
• 33:00
  Speaker 1: Exactly, it's structurally feminized. Compared to the straight rims. It
• 33:04
  Speaker 1: proves that this neuroanatomical variation isn't a unique artifact of
• 33:08
  Speaker 1: human society or culture. It is an evolved biological variation
• 33:12
  Speaker 1: in mammalian brain structure, and.
• 33:14
  Speaker 2: Modern technology allows us to look beyond microscopic neuron clusters
• 33:18
  Speaker 2: and examine macro level structural differences in living brains. This
• 33:22
  Speaker 2: brings us to the neuroimaging work of Ivankasavich in Sweden.
• 33:26
  Speaker 3: What did she do?
• 33:27
  Speaker 2: Her team utilized MRI and PEAT scans to analyze the
• 33:31
  Speaker 2: overall symmetry of the brain's hemispheres alongside mapping the internal.
• 33:35
  Speaker 1: Neurowiring Okay, what patterns emerged from the scans?
• 33:38
  Speaker 2: They discovered a fascinating pattern of cross sex shifts in
• 33:42
  Speaker 2: heterosexual men in lesbians, the brain exhibits structural asymmetry. The
• 33:47
  Speaker 2: right hemisphere is slightly larger than the last like how
• 33:50
  Speaker 2: much larger? Approximately two percent larger in straight men and
• 33:53
  Speaker 2: one percent larger in.
• 33:54
  Speaker 3: Lesbians okay, and the other groups.
• 33:56
  Speaker 2: Conversely, when they scanned gay man and straight women, their
• 33:59
  Speaker 2: brain sans were remarkably symmetrical. Both cerebral hemispheres possessed essentially
• 34:04
  Speaker 2: identical volumes.
• 34:05
  Speaker 1: Oh wow, gay men's brains structurally resembled straight women's brains
• 34:10
  Speaker 1: and lesbian's brains resembled straight men's.
• 34:13
  Speaker 2: Yes. Furthermore, when analyzing the amigdala, the region governing emotional
• 34:17
  Speaker 2: processing and the fight or flight response, they mapped the
• 34:20
  Speaker 2: neural pathways. Gay men and straight women shared similar wiring
• 34:24
  Speaker 2: patterns with their amigalas connecting primarily to regions involved in
• 34:28
  Speaker 2: internal mood regulation and anxiety. Lesbians and straight men shared
• 34:33
  Speaker 2: a different wiring pattern, connecting more directly to the sensory
• 34:36
  Speaker 2: motor cortex region's tasks with translating emotion into physical action.
• 34:41
  Speaker 1: It is an incredibly compelling visual narrative, but I want
• 34:45
  Speaker 1: to step in with a crucial critical thinking moment regarding
• 34:49
  Speaker 1: the mathematical statistics used to support these claims.
• 34:52
  Speaker 2: Oh this is important.
• 34:53
  Speaker 1: I recently read a skating critique of the Savic study
• 34:56
  Speaker 1: authored by an astrophysicist who runs a blog called.
• 34:59
  Speaker 3: In the Dark.
• 35:00
  Speaker 2: The intervention of an astrophysicist in neurobiological peer review is
• 35:04
  Speaker 2: exactly why interdisciplinary scrutiny is.
• 35:06
  Speaker 1: Vital, Because the blogger tore into the statistical methods the
• 35:10
  Speaker 1: Swedish researchers utilized to prove the brains were asymmetrical. To
• 35:13
  Speaker 1: measure asymmetry, you have to create a ratio.
• 35:16
  Speaker 3: You divide the.
• 35:17
  Speaker 1: Volume of the left hemisphere by the volume of the
• 35:19
  Speaker 1: right hemisphere right.
• 35:20
  Speaker 2: If the two sides are perfectly symmetrical, the ratio is
• 35:22
  Speaker 2: one exactly, but division is a standard mathematical operation. Where
• 35:27
  Speaker 2: is the.
• 35:27
  Speaker 1: Flaw Well in advanced probability theory, when you take two
• 35:31
  Speaker 1: independent variables that have a normal Bell curve distribution and
• 35:34
  Speaker 1: you divide them by each other, the resulting numbers do not.
• 35:38
  Speaker 3: Form a normal Bell curve.
• 35:39
  Speaker 2: What do they form?
• 35:40
  Speaker 1: They create something known mathematically as a Kachi distribution. A
• 35:44
  Speaker 1: Kauchi distribution is an absolute nightmare for standard statistics because
• 35:49
  Speaker 1: it possesses incredibly long, undefined tails. The variance is infinite
• 35:54
  Speaker 1: because the numbers are so close to one. Tiny fluctuations
• 35:58
  Speaker 1: create massive, unpredictable.
• 36:00
  Speaker 2: Outliers, meaning the standard deviation is fundamentally meaningless in a
• 36:04
  Speaker 2: Kachi distribution exactly.
• 36:06
  Speaker 1: But the neurobiologists applied standard run of the mill bell
• 36:09
  Speaker 1: curve statistical tests like T tests to this Kauchi distribution
• 36:13
  Speaker 1: to generate their P values and claim their findings were
• 36:16
  Speaker 1: highly significant.
• 36:17
  Speaker 2: Which is a mathematical error.
• 36:18
  Speaker 1: And even worse, to make their data look cleaner, they
• 36:21
  Speaker 1: actually deleted a key outlier data point from their calculations.
• 36:25
  Speaker 1: In a standard distribution, dropping a massive outlier might be justifiable,
• 36:29
  Speaker 1: but in a Kachi distribution, massive outliers are mathematically expected.
• 36:33
  Speaker 1: By deleting it, they manipulated the math. The astrophysicists demonstrated
• 36:38
  Speaker 1: that their mathematical proof was fundamentally flawed.
• 36:41
  Speaker 2: That critique highlights a pervasive issue in neuroscience, whereas small
• 36:45
  Speaker 2: sample sizes and complex statistical models frequently lead to false positives.
• 36:50
  Speaker 1: Right, it doesn't necessarily mean the researchers are entirely wrong
• 36:53
  Speaker 1: about brand symmetry, but it demonstrates that their evidence is
• 36:56
  Speaker 1: significantly weaker than they claimed. I bring this up not
• 37:00
  Speaker 1: to entirely debunk the Savik brain scans, but to remind you,
• 37:04
  Speaker 1: the listener, that we must constantly interrogate the math. Science
• 37:07
  Speaker 1: is not an absolute dogma handed down from on high.
• 37:10
  Speaker 1: It is an ongoing, messy, intensely debated process.
• 37:14
  Speaker 2: Well said, but if we synthesize the genetic data, the
• 37:18
  Speaker 2: epigenetic models, the birth order statistics, and the anatomical dassections.
• 37:22
  Speaker 2: They all heavily point toward a profound biological basis for orientation.
• 37:26
  Speaker 2: They really do, and that synthesis brings us face to
• 37:29
  Speaker 2: face with the ultimate overarching question, the Darwinian paradox AHH.
• 37:34
  Speaker 3: The evolutionary puzzle.
• 37:36
  Speaker 1: If we accept that these biological differences are hardwired and
• 37:39
  Speaker 1: genetically linked.
• 37:40
  Speaker 3: Why do they exist?
• 37:41
  Speaker 1: If the entire premise of evolutionary fitness is predicated on
• 37:44
  Speaker 1: surviving long enough to pass your genetic code to the
• 37:46
  Speaker 1: next generation through direct reproduction, wouldn't exclusive homosexuality be selected
• 37:52
  Speaker 1: out of the gene pool immediately? It appears completely maladaptive
• 37:55
  Speaker 1: on the surface.
• 37:56
  Speaker 2: It does. But to resolve the paradox, we have to
• 38:00
  Speaker 2: completely reframe how we view human sexuality. We tend to
• 38:04
  Speaker 2: view it strictly through a reproductive lens, but that ignores
• 38:07
  Speaker 2: basic human anthropology in what way. Unlike the vast majority
• 38:11
  Speaker 2: of mammals, human beings do not possess a specific heat
• 38:14
  Speaker 2: or rigid mating season.
• 38:15
  Speaker 1: We are continuously sexually receptive year round.
• 38:18
  Speaker 2: Yes, because of that biological reality, the overwhelming majority of
• 38:23
  Speaker 2: human sexual activity is entirely nonprocreative.
• 38:26
  Speaker 3: So what's its purpose?
• 38:27
  Speaker 2: Then? Evolution repurpose sex to function as social glue. It
• 38:31
  Speaker 2: builds emotional intimacy, diffuses tribal tension, and creates complex pair
• 38:35
  Speaker 2: bonds that hold communities together.
• 38:37
  Speaker 1: That makes a lot of sense. Furthermore, the assumption that
• 38:40
  Speaker 1: non heterosexual people do not reproduce is historically and factually inaccurate.
• 38:46
  Speaker 1: Societal pressures, bisexual behavior, and alternative reproductive strategies ensure that
• 38:51
  Speaker 1: these genes absolutely do get passed on.
• 38:53
  Speaker 2: Exactly by moving away from viewing sex solely as a
• 38:57
  Speaker 2: reproductive transaction, evolutionary biologists have hypothesized specific mechanisms that actively
• 39:04
  Speaker 2: preserve same sex attraction in the gene.
• 39:06
  Speaker 1: Pool right like the kin selection hypothesis frequently referred to
• 39:10
  Speaker 1: colloquially as the gay uncle fury yes kin selection break
• 39:14
  Speaker 1: down the mechanics of kin selection.
• 39:15
  Speaker 2: For us, evolutionary fitness is not merely about passing on
• 39:19
  Speaker 2: your own direct DNA. It is about ensuring the survival
• 39:22
  Speaker 2: of your genetic lineage. You share fifty percent of your
• 39:25
  Speaker 2: DNA with your siblings, and you share twenty five percent
• 39:28
  Speaker 2: of your DNA with your nieces and nephews. I follow
• 39:30
  Speaker 2: if an individual does not expend their energy, food, and
• 39:33
  Speaker 2: protective resources on raising direct offspring. They possess a surplus
• 39:37
  Speaker 2: of resources.
• 39:38
  Speaker 1: And they redirect those surplus resources toward the extended family.
• 39:41
  Speaker 2: Precisely by helping their siblings raise their children, Those children
• 39:45
  Speaker 2: experience a significantly higher rate of survival in harsh evolutionary environments.
• 39:50
  Speaker 2: Ensuring the survival of your nieces and nephews is an
• 39:53
  Speaker 2: incredibly effective backdoor strategy to guarantee that twenty five percent
• 39:57
  Speaker 2: of your own genetic code survives.
• 40:00
  Speaker 1: So over thousands of generations, this localized helper role provide
• 40:04
  Speaker 1: such a massive survival advantage to the family's overall genetic
• 40:08
  Speaker 1: line that the biological traits predisposing someone to same sex
• 40:11
  Speaker 1: attraction are carefully preserved.
• 40:14
  Speaker 2: It's an elegant mathematical theory.
• 40:15
  Speaker 1: It is, But is there empirical evidence that gay people
• 40:19
  Speaker 1: actually exhibit this behavior. I know plenty of straight uncles
• 40:22
  Speaker 1: who are incredibly generous, and plenty of gay uncles who
• 40:24
  Speaker 1: are totally aloof fair point.
• 40:27
  Speaker 2: When researchers initially surveyed men in the United States and
• 40:29
  Speaker 2: the United Kingdom, they found no statistical difference in generosity
• 40:33
  Speaker 2: or family affinity between gay and.
• 40:34
  Speaker 3: Straight manas oh, so the theory fell flat.
• 40:36
  Speaker 2: It appear flawed. However, evolutionary psychologist Paul Vasy realized that
• 40:41
  Speaker 2: Western hyperindividualistic societies are terrible environments to test evolutionary tribal theories.
• 40:47
  Speaker 3: Where did he go? Instead?
• 40:48
  Speaker 2: He shifted his research to Samoa.
• 40:50
  Speaker 3: Ah.
• 40:50
  Speaker 1: Samoa is a collectivist culture, and they possess a socially
• 40:54
  Speaker 1: recognized third gender called the fophaphene.
• 40:58
  Speaker 3: Right.
• 40:58
  Speaker 2: Yes, the Faffafene are biological males who are attracted to men,
• 41:02
  Speaker 2: but they exist socially distinct from both traditional men and women.
• 41:06
  Speaker 2: Right because the Faphatheene are deeply integrated into the collectivist
• 41:09
  Speaker 2: family structure, Vacy hypothesized this was the ideal environment to
• 41:14
  Speaker 2: observe kin selection in action.
• 41:17
  Speaker 3: And what did he find?
• 41:18
  Speaker 2: His studies revealed that the papatheene exhibited significantly higher avuncular
• 41:22
  Speaker 2: or uncle like tendencies compared to straight Samoan men. They
• 41:26
  Speaker 2: were far more willing to babysit, purchase toys, tutor children,
• 41:30
  Speaker 2: and contribute financially to medical care.
• 41:33
  Speaker 1: But the crucial evolutionary detail is exactly who they were
• 41:36
  Speaker 1: willing to help. Right, They weren't just exhibiting general blanket
• 41:39
  Speaker 1: generosity to the whole village.
• 41:41
  Speaker 2: No, they were not.
• 41:41
  Speaker 1: Their avuncular tendencies were highly specifically targeted at their own
• 41:45
  Speaker 1: biological nieces and nephews. They did not exhibit the same
• 41:49
  Speaker 1: level of resource sharing for unrelated kids in the community.
• 41:52
  Speaker 2: Evolutionary psychologists classify this as an adaptive cognitive dissociation, meaning
• 41:58
  Speaker 2: it is a highly targeted, evolved psychological mechanism designed to
• 42:02
  Speaker 2: protect shared DNA. Vac's research provides incredibly compelling real world
• 42:07
  Speaker 2: evidence for the kin selection hypothesis, suggesting that in the
• 42:11
  Speaker 2: proper cultural context, same sex attraction is deeply intertwined with
• 42:15
  Speaker 2: the evolutionary survival of the extended family unit.
• 42:18
  Speaker 1: The idea that homosexuality evolved not as a genetic error
• 42:22
  Speaker 1: but as a mechanism of communal survival and love is
• 42:25
  Speaker 1: genuinely beautiful. It is are there other evolutionary theories at
• 42:29
  Speaker 1: play here?
• 42:29
  Speaker 2: Evolutionary mechanisms rarely operate in isolation. Another major hypothesis is
• 42:34
  Speaker 2: antagonistic pleaotropy.
• 42:35
  Speaker 1: We discussed plaotropy earlier. When one gene influences multiple traits.
• 42:39
  Speaker 2: Exactly, antagonistic pleaotropy proposes that the exact same genetic package
• 42:44
  Speaker 2: that increases the probability of same sex attraction in the
• 42:46
  Speaker 2: male might cause hyperfertility when that exact same genetic package
• 42:50
  Speaker 2: is present in a female.
• 42:52
  Speaker 3: Okay, let me make sure I understand.
• 42:53
  Speaker 1: So, if a mother possesses this specific gene variant, she
• 42:57
  Speaker 1: passes it to her son, the son is and does
• 43:00
  Speaker 1: not directly reproduce. However, she also passes that exact same
• 43:04
  Speaker 1: gene variant to.
• 43:05
  Speaker 2: Her daughter, and the daughter becomes exceptionally fertile and successfully
• 43:09
  Speaker 2: raises say, six children instead of the average two.
• 43:12
  Speaker 3: Wow.
• 43:13
  Speaker 1: So the biological trade off is an evolutionary net positive
• 43:16
  Speaker 1: for the family line. The reproductive loss of the sun
• 43:19
  Speaker 1: is overwhelmingly compensated for by the daughter's hyperfertility. The genetic
• 43:24
  Speaker 1: traits survive and proliferate throughout the population.
• 43:27
  Speaker 2: That is the core of antagonistic pleotropy.
• 43:30
  Speaker 1: We have covered a massive expanse of biological territory today.
• 43:33
  Speaker 3: We have traversed from.
• 43:34
  Speaker 1: The fluid scales of kinziin kline, zoomed down into the
• 43:37
  Speaker 1: microscopic type setting of our DNA through genome wide association studies,
• 43:42
  Speaker 1: waded through the hormonal baths of the.
• 43:44
  Speaker 2: Room, measure the bone growth in our fingers.
• 43:46
  Speaker 1: Explore the immune responses of mothers, dissected the hypothalamus, debated
• 43:50
  Speaker 1: the long tails of statistical math, and traveled to Samoa
• 43:53
  Speaker 1: to observe evolutionary family dynamics.
• 43:55
  Speaker 2: In action, it is a breathtakingly complex mosaic of human.
• 43:59
  Speaker 1: Biology, synthesizing everything we've explored. The absolute clearest takeaway is
• 44:04
  Speaker 1: that there is no single gay gene, There is no
• 44:06
  Speaker 1: simple binary choice, and there is no purely environmental how
• 44:11
  Speaker 1: you were raised cause now sexual orientation is an intricately
• 44:15
  Speaker 1: woven tapestry of thousands of polygenic variants, the crucible of
• 44:19
  Speaker 1: prenatal hormones, maternal immune responses, and deep ancient evolutionary survival strategies.
• 44:25
  Speaker 2: This leads me to a final thought something for everyone
• 44:27
  Speaker 2: listening to Mollover. We expend an enormous amount of energy,
• 44:31
  Speaker 2: both in scientific research and in societal discourse, attempting to
• 44:35
  Speaker 2: force human attraction into rigid, neat little boxes.
• 44:38
  Speaker 1: We desperately want the clean X ray exactly.
• 44:41
  Speaker 2: We want to label someone as exclusively straight, gay or by,
• 44:45
  Speaker 2: and then we want to find the exact biological switch
• 44:48
  Speaker 2: that have flipped them into that specific category.
• 44:50
  Speaker 1: We want the math to be simple and the biology
• 44:52
  Speaker 1: to be binary.
• 44:53
  Speaker 2: But when we observe the incredible sexual fluidity over a lifespan,
• 44:57
  Speaker 2: the polygenic nature involving thousands of overlapping genes, the delicate
• 45:02
  Speaker 2: epigenetic balances mediating hormone exposure, and the clear evolutionary usefulness
• 45:07
  Speaker 2: of diverse sexual behaviors, we have to ask a larger question.
• 45:10
  Speaker 4: What's that?
• 45:11
  Speaker 2: What if the true biological default of humanity isn't strict
• 45:15
  Speaker 2: categorization at all? What if the biological baseline is an inherent,
• 45:19
  Speaker 2: deeply adaptable spectrum.
• 45:20
  Speaker 1: The X ray isn't broken, We've just been using the
• 45:23
  Speaker 1: wrong machine to look at a kaleidoscope. Thank you all
• 45:26
  Speaker 1: so much for joining us on this exploration today. If
• 45:29
  Speaker 1: you enjoyed this journey into the biology of attraction, please
• 45:32
  Speaker 1: hit that five star rating on your app, leave a review,
• 45:34
  Speaker 1: and share it with friend who loves a good scientific mystery.
• 45:37
  Speaker 1: Until next time, stay curious, keep questioning the simple answers,
• 45:40
  Speaker 1: and we'll catch you on the next deep exploration here
• 45:43
  Speaker 1: on Beyond Infographics, m