Hey everyone, welcome to the Drive

Podcast. I'm your host, Peter Aia.

Carol, thank you so much for coming out

to Austin. Great to great to meet you in

person.

>> Thank you so much for having me. I'm

thrilled to be here.

>> This is a topic that we we talk a lot

about on the podcast, but usually from a

pretty narrow lens, right, which is in

the form of replacement. Um, we talk

about hormones. um both in men and women

uh sex hormones and we talk about how

they they wax and wayne as a as an

individual ages. We obviously then talk

about you know sort of the medical use

of them but I don't think we've spent

any time understanding the more basic

fundamentals of these hormones, the role

they play in our evolution. Um, and

anecdotally,

you know, I I'll just share with you

kind of the observation that any parent

probably has uh if they have male and

female children, right? So my my first

child was a girl and

I we my wife and I very very stupidly

and arrogantly thought we were the

perfect parents because like she was so

well behaved and we were like what do

all of these other parents with their

boys running around misbehaving? Like

what are they doing wrong? And like how

could we teach them how to be as good as

we are? I mean, we didn't actually say

that, but there was undoubtedly an

annoying smuggness to us.

Um, and if you believe in a god, that

god smacked us into our place with two

boys that followed who were for all

intents and purposes treated the same

way, socialized the same way. And there

is a level of aggression in them, a fury

in them that I've never seen probably

unless I were to go back and hear

stories of what my mom said I was like.

How old are your boys now?

>> Uh, eight and almost 11.

And they're a diff they're not I

wouldn't say they're a different sex. I

would say they're a different species.

>> Yeah, I was just going to say that.

>> Yeah. So, all of that is to say

I don't I don't feel we did anything

different and yet they couldn't be more

different. And I I appreciate that

that's not going to be the case for

every parent. Um, but I also don't know

how much, well, what I hope to learn is

how much testosterone has to do with

that because I also am under the

impression that at this age the

testosterone levels wouldn't be that

much different. And I understand and

we'll probably talk about the

differences in testosterone levels

during the embryologic phase because

obviously that led to the differences.

But anyway, with that as backdrop,

>> yeah,

>> how did you get interested in this

topic?

>> Great. Okay. So, I want to make sure to

come back to everything that you just

said. Um,

so how did I get interested? I'm going

to start at the beginning, which is that

I grew up with three older brothers, and

I'm assuming that this had something to

do with my interest in testosterone. We

They were different than I was I am in

some in some consistent ways. I don't

think I thought much about that. And I

think that probably

made me really want to understand what

motivates um male behavior in general

and why it's different from female

behavior.

That wasn't sort of an idea that I had

when I was in college that I was going

to go study this, but I did become

intensely interested in the evolutionary

origins of human behavior in general and

what makes us different from other

animals. And that happened, I think,

because of traveling. I traveled

to a lot of different places in the

world mostly by myself uh during and

after college and there were such

extreme differences culturally. Egypt

with your family's Egyptian. That was

one of the places I went that really

freaked me out because I that really

shook me um because the cultural

differences

>> were so profound in terms of the

incredibly important role that sex plays

in social life and the segregation uh

and different rules that applied to

males and females. I was I was alone

traveling by myself as a young woman,

totally ignorant of what I was getting

into in Egypt. I was harassed endlessly.

Um, some of that was my fault for not

understanding the culture well enough

and what I was getting into. Uh

so this combination of

being immersed in not only different

societies that treated sex and sex roles

very differently but also different

ecologies. I spent some time um in

Africa and Kenya and Tanzania and got

really interested in all of the animal

behavior and why we are different from

other animals etc. So I had a whole

other career before graduate school and

I ended up leaving that career and

applying uh to Harvard to try to do a

graduate degree where I could um do more

to understand the evolutionary basis of

human behavior. I ended up uh getting

rejected and I just persisted and then

was offered this job out in Uganda

studying chimps for what was supposed to

be a year. And that is what really

triggered my interest in sex differences

and testosterone because

we I think to a certain extent are

indoctrinated uh to believe that most

human sex differences are cultural or if

you think that they're not it it's

better you don't say that out loud to

too many people are in the wrong place.

Uh, so when I spent time with the

chimps, I was really blown away by the

ways that the sex difference in the sex

differences in the chimps paralleled

human sex differences. Of course, not

exactly the same, but the very basic

things that you just described um, even

just in terms of energy and aggression

are present in the chimps in terms of

being higher in the males and lower in

the females. And I'm getting goosebumps

because the reasons for that are so

profound and far-reaching and start with

sperm and egg. And that's what sex

really is about is the um not just the

ability to produce sperm or eggs, but

kind of the way that the organism is

designed and the uh reproductive

phenotype including body and behavior.

And then that in humans plays out in

these really complex ways in terms of

social systems. So I thought I really I

got interested in testosterone because

this is one thing I could grab on to

that links very clearly humans,

chimpanzees and every other mammal in

terms of um males having much higher

levels than females. And it's not just

mammals. There are other forms um of

steroid hormones that uh other species

have but this is um pervasive and just a

very powerful way to understand

approximately that means what's

happening sort of here and now in the

organism why the sexes are different and

then there are these deep evolutionary

pressures that have to do with

reproductive strategies for organisms

that produce sperm versus organisms that

produce eggs and so then I ended

uh reapplying to Harvard and getting

into the grad program there and I did my

dissertation on testosterone and sex

differences in cognition

um and the way we think and process

information and I had men watch sexy

videos and also videos of dental surgery

and collected uh their saliva and

measured their testosterone in the lab

and uh and then I just stayed on at

Harvard uh mostly just teaching. So, I

want to go back to something you you you

sort of said a second ago, which is the

distinction between mammals and non-

mammals. Uh, and I never really thought

of it until you said this, but if if I

were to

look at a a male great white shark and a

female great white shark, first of all,

do they have testosterone in them as the

androgen or sex form?

>> Vertebrates, most vertebrates will have

testosterone or something very, very

close

>> to testosterone. Yep. Now, if you again

go back to the example of great white

sharks,

>> yeah,

>> typically the females are larger. I

would reckon they're just as aggressive

as the males. Is that reflected in

comparable levels of testosterone in

those species?

>> So, sharks I don't know about

specifically, but first of all, uh males

are not always bigger than females.

Males will do whatever they need to do

generally to compete for mates. And in

many species, it's not uh to be larger.

Also there are differences in the

ability to defend a territory or defend

mates in air and water and land and

that's really a interesting way to

understand some male competitive

strategies.

So, but generally when in the species if

the female is just as aggressive, often

it's uh maternal aggression and not

necessarily uh mate competition. And if

it's

>> uh maternal aggression tends to be

mediated more by estrogen than

testosterone, even in hyenas that uh

which are very difficult to tell apart,

the females are very difficult to tell

apart from the males. They have this

clitoris that looks exactly like a penis

and experts often can't even tell the

difference. They're highly aggressive.

Um, and that seems not to be mediated by

adult in the adult at least with uh by

comparable levels of testosterone. There

seems to be potentially something going

on in early development. But often I I

don't know of good evidence that

testosterone acts similarly in females

to mediate um say mate aggression that's

we'll say mating aggression.

>> So so just make sure I understand in the

hyenas if you took an adult male and an

adult female hyena would they have

similar levels of testosterone and

estrogen?

>> No the males would be higher.

>> The males would be higher. Um,

>> despite the fact that phenotypically

they look the same and they're both

equally aggressive.

>> I believe they're either just as a

aggressive if not more so. I think

they're I believe that they're dominant

to the males.

>> Got it.

>> Uh, and there's something going on with

potentially adrenal and like maternal

adrenal androgens when the fetus is

developing that becomes the aggressive

female. But I don't think it's uh

completely worked out. I haven't looked

at the literature on that in ages. So

the the

extent of my recollection from um from

medical school on this topic was that

and again we can come back and talk

about the edge cases but

99.9% of cases are either XX or XY

right in terms of humans humans. Yes.

>> Yeah. Right. So we can talk about

Turners and Klein filters and things

like that later, but in the 99.9% of

cases of XX and XY,

what are the steps

and um how do they involve sex hormones

that create the phenotypic differences

in the embryo?

>> Yes. So phenotypic um we'll just stick

to the body and then we can also talk

about the behavior.

>> Yes. Yes. Exactly. That's what I want. I

just want to start with let's get

through the first nine months

>> and then like let's help understand how

those those two options of chromosomes

lead to two different body types.

>> And I just want to say right at the

outset that we have a sex determination

system that relies on chromosomes, but

not every animal does. So chromosomes do

not equal sex. And birds have used

chromosomes, but they have a different

system where the female is the one that

has hetererozygotic um chromosomes. So

there's temperature dependent sex

determination. So people should not

confuse uh the sex hormones themselves

with the definition of sex. However,

>> the chromosomes are the sex hormones.

>> Sorry, sorry. Sorry. Did I say sex

hormones? Sex chromosomes. Sorry.

>> Yes.

>> Uh thank you. So se the in in mammals

the chromosomes determine sex but do not

define sex. Again across sexually re

almost all sexually reproducing

organisms it's the um gameamt type that

the organism is basically designed

around uh the re that the reproductive

system is designed around that defines

sex. So and also we can have other

organisms have um can be hemaphroditic

have uh produce both gameamt types at

the same time or they can be sequential

hermaphrodite. So I just want to

>> yep

>> get that out first. So in humans the uh

mom the mother's egg is always the the

sex chromosome is always going to be an

X that it donates um in its egg and it's

going to combine with a sperm. 50% of

the sperm are going to have a Y sex

chromosome and 50% of the sperm are

going to have a X chromos uh gonna have

an X in general. So those two uh combine

and the developing embryo is going to be

either XX and XY. So

let's just start with the XY.

Uh so you were an XY. I had a son who

was an exy, which is weird for women

because they h they will have a

something inside of them that has

testicles that's producing that produce

testosterone. Uh, which I think is

interesting. And so an XY fetus

around

uh five or six weeks.

I should just say that XX and XY are

both uh

almost completely they're almost

identical until that time.

>> And the Y chromosome has a gene on it

called the sex determining region of the

Y chromosome that produces a protein

called the SRY protein. And this is a

very important protein because it

triggers the differentiation of the

undifferentiated gonad. So what's really

cool and interesting is that before that

time we all have a gonad that can become

>> both

>> either one. It can become um testes or

it can become ovaries. And that's sort

of an amazing design. And that's

evolution's way of not wasting energy,

not have having to have two

>> two systems,

>> two different systems that one develops

and the other gets discarded at least in

terms of the gonads. So they come first.

And

so in terms of sexual differentiation

that means that for XY

um individuals the gonads are going to

develop along the testicle route and

without the SRY gene they will by

default when I say by default that

doesn't mean that nothing else has to

happen. other genes have to be expressed

and and that's an active process. It's

not a passive process. But without the

SRY gene, those undifferiated gonads

will differentiate in the female

direction to form ovaries. So, so I

remember my overly simplistic and this

is almost 30 years ago, but I could have

sworn I used to think about this in the

embryology class as by default we are

female and this gene had to turn on to

basically take the X-wise and make them

male phenotypically. But that's

obviously oversimplified.

>> Yes. So, in some ways that is true. Uh

I would not

put it that way be but

by default you the individual will

develop say female

>> because if you have an XY that is

missing that region you will be

phenotypically

female but chromosomally male.

>> So you will be uh chromosomally male.

Sure. um

you will not develop but you won't

develop functional ovaries. Correct. You

won't be able to reproduce that but you

would look for all intents and purposes

you would look female. Correct.

>> Yes. So your external genitalia would

appear to be female

>> and we we'll get into those cases. Again

these are kind of these edge cases.

>> Yeah. If you think about what the

genitalia look like in a early

developing fetus, it looks female. It

doesn't have to change that much. It

gets bigger. Y

>> but to if you take what looks like um

even adult female genitalia, basically

you modify the clitoris and and the

labia to get what looks like um typical

male genitalia. So that has to do a lot

of growing and changing. And it's like

that in in the embryo or sorry in the in

the fetus. So if we're going down the

the male route, you get the expression

of SRY. And what that does is it um

causes certain cells in this

undifferentiated gonad to develop into

first uh leig cells and then later

cerolely cells. So that's happening and

then later ovarian uh differentiation

takes place.

So two things happen. The lady cells

start producing testosterone

uh first. And

I'm going to go back and just talk about

the wolfian ducts and the malarian

ducts.

>> Oh my god, I have not heard that term

since medical school. I I what a blast

from the past. Okay, so this is du

cts, not duck like quack-quack. So these

are ducted systems. Yeah.

>> And so here's another kind of cool

thing. So we start out with this

>> um

two primordial or primitive gonads that

can become either

>> and they're high. I remember they're in

the almost in the chest. And so

obviously the males have to descend into

what becomes the scrotum and the females

just stay there.

Um and and that seems very sensible.

>> You you know we still don't completely

understand why males take all this

valuable

>> stuff and keep it outside of their body.

That's a whole other

>> maybe temperature regulation.

>> Yeah. I wrote about this in my book and

I researched it um

pretty thoroughly and came up with no

answer because elephants uh have their

testicle elephants and whales and um but

I think elephants might there's oh one

other vo or something that has their

testes inside but all other mammals it's

outside and yes it's there certainly is

temperature regulation uh but then why

don't we have the system however it is

that the elephants can get

genetic.

>> I'm just going to take you down a stupid

detour for your next book.

>> Um, we were at my younger son's uh

baseball party at the end of the season.

And so now picture at the, you know, at

the time a bunch of, I don't know, 27y

old boys running around the pool playing

baseball, playing football, goofing off.

And me and the dads were sitting there

hanging out and we were observing their

behavior and and I came up with this

observation which is

there's estimated to be about 110

billion humans that have lived right

over the past 250,000 years inclusive of

of course the eight or so billion that

are alive today. And just watching this

small group of 20, you could already see

the number of times one boy would walk

up to the other and sort of flick him in

the nuts. Okay. And I was like, "All

right, to the dads."

>> How many times How many times in the

history of 250,000 years has one male

gone up to another male to flick him in

the nuts? How what's that number?

>> So it go it's goes back. So the chimps

did this.

>> Well, so but let finish the punch line.

The punch line is whatever that number

is, it's enormous.

>> Yeah.

>> Now, what's the number of females that

have gone up to another female and gone

and tried to flick them in the clitoris?

Like zero.

>> There is sometimes a little breast play,

I guess, teenagers, but nothing like

what boys.

>> Is this like what it's you're talking

about a ratio of 0 to 87 bill432

million.

>> All right. Give me your hypothesis about

why this happens.

>> I mean, my only hypothesis is that boy,

males are idiots. Like, it's such an

evolutionary stupid thing to do to like

that's a very precious part of real

estate.

>> That's the point. So, why would they do

that?

>> So, maybe it's threaten. It's like

basically I'm going to make sure you

can't reproduce. Like, I'm going to be

dominant. I'm going to I'm going to

reduce your probability of reproduction.

>> So, these are kids who are good friends

usually, right?

>> Yes.

>> And only a good friend could do it.

>> Yeah. Well, only a good friend will get

away with it.

>> Like if a stranger did it, then you're

going to come across.

>> Okay, so that so that's the point, I

think. Um,

>> so male intimacy involves insults.

Uh, the the the harsher the insult

somehow the more intimate unless it's

rejected like you just described with

the flick. So chimps,

>> and this was amazing to see because I

didn't know about it. uh when they're in

a high stress or or conflict situation

or there has been a conflict, they will

uh the subordinate will cup the balls of

the dominant one and and and they also

sort of play sex from behind kind of,

but it's this intimate trusting weird

situation where I think it really is

saying I'm down for you. I'm not gonna

hurt you. I'm holding your testicles and

you can trust me. I think, you know, I I

don't know, but uh that's that's

interesting.

>> It it just blows my mind because again,

the dads, we sat around and we laughed

hysterically at this because most of us

have daughters and we're like our our

girls have never once behaved in this

way.

>> Yeah.

>> Anyway, sorry, carry on. I apologize. So

I'm going to be

>> So there's all these things we don't

understand and one of them is why would

you leave this precious real estate

outside your body if you could

potentially thermmore regulate inside

the body.

>> I mean maybe there's an answer now and I

haven't found it and someone will you

know write in

>> we'll hear about it in the comment

section. Yeah.

>> Um so I'm just going to go through the

ducts a little more quickly. That's

there's two different systems. So the

wolfian ducks become what I'll just say

is the male internal plumbing and

thearian malarian ducts become what is

the female internal plumbing.

>> So what's what's important is that the

lady cells produce testosterone which

stabilizes the development of the

wolfian ducts. The testicles have to

produce uh two hormones. Lady cells

produce testosterone to stabilize the

wolfen ducts to connect the um sperm

producing organ to the delivery system

ultimately which is the penis and they

have to cause the degeneration of the

malarian duct. So that's antimmalarian

hormone and testosterone. So healthy

testes and this is important when we

talk about uh the disorders or

differences of sexual development.

Healthy testes will have those effects.

And you can also think about well what

happens if they can't produce

antimmalarian hormone or what happens if

there's no receptor for testosterone or

no no receptor for malarian hormone.

>> And by the way is there at any point is

any of this testosterone being converted

to DHEA in any meaningful amount? Not

that I know of. DHT for sure. Yep.

That's extremely important and that

comes next. Uh so I would like to

>> Sorry, I meant DHT. I'm sorry. I'm

sorry. Yeah. Yeah. So I I want to make

sure I can just talk about it a little

bit now. Uh so so that conversion is via

the enzyme five alpha reductase that's

present that's present in uh high

concentrations in the genital tissue. So

what's interesting about this is that

you have a mechanism to achieve high

concentrations of a more potent androgen

without that uh having to circulate

through the general circulation which

you do not want in a developing fetus.

You want to be able to control um the

development of the penis say which is

one of the things that DHT does. It

takes the uh so this so so the genital

tubrical can become the clitoris or the

penis essentially in the presence of

testosterone and functional uh five

alpha reductase it becomes a penis the

labia grow and then fuse to become the

scrotum uh and that and also the

prostate the uh DHT is necessary for

full prostate development and can later

uh sustain the function of the prostate

so what's it it is interesting because

it is this solution to in to providing

very strong androgenic signals in the

tissues that need it without wasting

energy on uh strong androgenic signals.

>> I've never actually unders I've never

thought about this until now. Is that

why DHT has such a high affinity for the

androgen receptor? You think? Yes. Is so

that you could permit it to only have a

local effect? Yes.

>> During embryologic development because

otherwise I don't know that it would

matter as much in me at this old age

that DHT is that much more potent than

testosterone. Right. So, I don't think

it would matter as much uh

>> because I'm I'm okay to be exposed to

circulating

androgens in a way that the fetus

presumably you wouldn't want.

>> I think that DHT is something like two

to five times more potent. So, and I

just

>> I thought it was even more than that.

>> It could be more. But what this means is

that it binds the receptor more tightly

and it stays on for longer, which means

that it um produces more of whatever the

protein is that it's um upregulating

because it's a steroid. Testosterone is

a steroid. Estrogen is a steroid. And

steroids, this is the way that they

typically act is by either inhibiting

but generally upregulating um androgenic

genes. So

yeah, I think that's super interesting.

And of course, there's a disorder five

alpha reductase uh deficiency where

individuals are

basically just typical males, but they

happen not to be able to produce DHT,

which seems not to, we can talk about

this later, but it seems not to have any

DHT is not what masculineizes the brain,

but it does masculineize external um

genitalia. So without that, you're going

to have what look like female genitalia

in a male. Yeah.

>> Whose otherwise typical male because the

testosterone works and the androgen

receptors are present.

>> Unfortunately, these

>> these are really really rare conditions

because that's

>> I mean these are Yeah, I I sort of It's

funny in medical school you you come

away thinking these things occur all the

time because of how much time you spend

studying these these very very rare uh

disorders. Um but but again fortunately

they're not common

>> but they do help I I used to teach a lot

about these cases because

uh yes they really help to understand

the typical pathway but also how

powerful even tiny little mutations in

little genes how powerful those

mutations can be and

uh I think it increases compassion when

we understand what the pathway is that

leads to these differences or disorders

how you know

>> because going back to that specific case

>> you have an individual that is born that

I assume at birth looks female

>> it depends where they're born if they're

born and this will become relevant if we

talk about this later in terms of sports

if they're born in places without a sort

of modern medical care often they are

sexed as uh female

But I think it becomes apparent quick

pretty quickly in childhood that that um

they're actually male. That's a whole

complicated,

>> right? Because they look male everywhere

else, right?

>> Uh

yeah, we should probably talk about that

later. But they the body the body will

look male once puberty hits. But there

is a lack of facial hair and other body

hair

>> and that do they have ovaries?

>> No no no testes. No ovaries.

>> No they have testes

>> but they haven't descended.

>> Uh they may or may not have generally.

So the the ones that really do appear to

be female and can even be uh yeah people

may believe that they're female until

puberty when they start developing male

musculature

>> uh

>> because then they're producing totally

normal testosterone levels. Yes. Just

not DHT.

>> That's right.

>> Which Yeah. The testosterone at this

point is the determining factor.

>> Um determining what?

>> Muscle mass, body hair, things like

that. Well, it can. If you don't make

DHT, some body hair will won't be

produced. You won't have full uh male

typical levels. You certainly won't have

any facial hair.

>> You won't have uh male generally, I

don't think you have male pattern

baldness.

>> Uh so the and and

the so the lack of facial hair really

makes a huge difference.

>> Yeah, that's so interesting.

>> Um because it gives a sort of more

feminine appearance to the facial skin.

So DHT is important. Um and and the the

reason part of why five alpha reductase

deficiency is relevant now is because uh

there are people who are sexed as female

and are legally female who are coming

from say a rural town in South Africa

because they've been running uh as a

female on female sports teams and then

or boxing for instance.

>> This is obviously the case we're all

familiar with. brings up complicated

social issues about what to do and that

really that means that we really do need

to understand the science there. And the

important thing from my point of view is

that um DHT has been clearly as I think

pretty clearly shown not to be uh

necessary for male typical patterns of

musculature and and other um physical

features that would give men an

advantage over women which is difficult

because sometimes these people have you

know been in a female social role

depending on where they

>> although that's also an easy experiment

to do. You could imagine giving a male a

five alpha reductase inhibitor from

birth.

>> Oh, from birth.

>> Like as a thought experiment, right? If

you took if you took a normal

chromosomally phenotypically normal male

and from the time they were call it 5

years old, you just gave them five alpha

reductase inhibitor.

>> Yeah.

>> All you're doing is turning their DHT

down to zero and doing nothing else.

You're basically asking the question,

will they develop normal musculature?

>> Yes. So Bessine Challenger Bessine and

at all have done that experiment and

there's no difference between uh this

animal and no they did it in humans.

>> How did they get an IRB for that?

>> I Yeah. Well, you know, I'm you know I

think you know his work. They've gotten

an IRB for a lot of um incredible

studies that are

>> would never be done today.

>> Super rigorous and gold standard and

>> Yeah. Interesting. Okay.

>> So, all right. You and I are probably

the only ones at this point this excited

about this discussion because we're now

so far down the weeds of embryology.

But, um, sort of bringing it back to the

surface, the takeaway here is that

XXXY start out for about 5 weeks

indistinguishable.

At about that fivew week mark, a gene on

the Y chromosome specifically begins to

trigger the differentiation pattern.

That differentiation pattern triggers

the transcription of hormones that then

transcribe

>> transcription of genes.

>> Transcription of genes that turn on

hormones that are going to

>> further activate and drive sex

differentiation.

>> So yes, thank you for that last piece.

Uh that's very important. So the

production of testosterone

in the testes,

this is really important and just

fundamental to understanding sex

differences. It's not that we have so

many different genes. So at the same

time, I should say there is we're

learning more about the role of the 70

to 100 genes on the Y chromosome, many

of which are crucial for uh typical

development of male uh reproduction and

and reproductive function.

uh but also it appears that there's some

role even prior to the production and

action of testosterone on the body and

brain. The there may be early expression

of genes on the Y chromosome that act in

the brain to shape later patterns of

behavior. Uh so that there's a lot of

work going on there to understand that.

Excuse me.

Um, so there are genetic differences and

I also want to say that the genetic

differences don't just stop at the

differences with those genes on the Y.

Uh, all the other genes are the same

except for the sex chromosomes, but

having one X versus two X's makes a huge

difference. It's extremely important. Uh

so typically so people think that the

that females completely silence one of

their X chromosomes

uh in each cell which is something that

basically does happen so that we don't

have a double dose of X chromosome genes

compared to males. So that's something

called a bar body.

>> But if that were true then wouldn't it

must be more complicated or else you

wouldn't have Turner syndrome.

>> It is so yes. So what happens is and

that's right and we can talk about

Turner syndrome but uh something like

20% and here someone might correct me

but I think around 20% of the genes on

the silenced X escape inactivation and

that turns out to be important that

there are some genes in females that

need where where the female needs the

double dose of those genes and if she

doesn't have the double dose

as in uh Turner syndrome. That's a

>> which we can define for folks as single

X chromosome

>> which presumably they got from mom and

then they didn't get a chromosome from

dad or do we know that

>> they can get it from mom or dad and

that's another rabbit hole we could go

down. There are imprinted genes um

depending on the the parental origin,

meaning certain genes are preferentially

expressed or suppressed in the mom's ex

versus the dad's for interesting

evolutionary reasons because the mom and

dad have

>> uh competing interests in what happens

to the kid.

>> And phenotypically, a woman with Turner

syndrome does appear phenotypically

female. Yes. But I believe she's not

able to reproduce.

>> That's correct. As far as I understand,

I think that there's some evidence that

there's technology now where where they

could

>> reprod but she's sterile and maybe

natural.

>> I think in some rare cases that can

happen, but generally the ovaries don't

uh

>> but her stature is distinctive, right?

She's going to be shorter

>> and there's a sort of

>> there's a sort of wider neck and a few

other uh characteristics,

>> but generally they're uh not Yeah. Yeah.

And and so um something about these 20%

or thereabouts of genes on the

supposedly silenced X chromosome are

clearly making the difference because

that would be the biggest difference you

would notice.

>> I don't know if that's the total uh

complete difference. I don't I don't

know enough about Turner but Turner's

but they turn out to to yes be important

and I don't even know if it's well

unders I think there is actually some

research on exactly which genes are

typically uh escaping but

>> and is it always the same genes

>> yeah

I don't know I don't know

>> okay

>> but so I just wanted to make the point

that in terms of the test so at this

point we have a high level of

testosterone in the fetus that is

approaching concentrations that uh in

male puberty. So this is not happening

in the female. This is a huge difference

and the reason it matters is because

testosterone

as a steroid is then going around and

acting as a transcription factor when it

uh binds with this receptor to alter

gene transcription on thousands of

genes. So uh that is happening in males

and not in females.

>> At about what stage of development? How

many months or weeks

>> we're talking? So I think around 8 weeks

it begins peaking around

15 to 20 weeks and then of course after

birth

>> it goes back down.

>> It well it goes down at birth but then

it goes up for uh peaking at 3 months

after birth and that's called mini

puberty. So this

>> I don't I don't even remember this.

>> Okay. So let because it's new you

probably didn't learn about it in

medical school. Now it's getting a lot

of attention.

>> But the point is somewhere in the second

early second trimester

that level of testosterone in a male

fetus is comparable to what it

>> it's lower. It's a it's not exactly as

high but it's very high.

>> But it's if a male in puberty is at

1,200 nanogs per deciliter this could be

600 nanogs per deciliter.

>> Maybe 400.

>> Okay.

>> Uh if I remember correctly

>> but still screaming high

>> but it's very high. And the point is

that this is affecting the development

of the brain. So I'm really interested

in behavior and from an evolutionary

point of view, what is going on

in this

early environment is extremely

important. The body is realizing, the

male body is realizing that it's going

to be a sperm producing animal. So the

brain is and we have very firm evidence.

We can't do these experiments in humans.

So people don't like it when all the

evidence comes from non-human animals,

but most of it does. And that's just

because we can't manipulate genes and

hormones and developing fetuses and see

to see what happens. We have some quote

natural experiments, but all the

evidence shows that testosterone is a

potent regulator of neural development

and differentiation from females, which

is why boys and girls aren't the same.

That is why it is 100% the reason and it

is 100% in my view uh this you know

>> this explains the birthday party

phenomenon.

>> Yes. If there could be new evidence that

comes out in humans, but all the

evidence we have points to testosterone,

>> socialization matters, right? If you

punish your kid for not playing mas,

being masculine enough, or being too

masculine, which happens because now

toxic masculinity and rough and tumble

play is supposed to be toxic. It's not.

It's healthy. It's necessary.

>> I didn't know that. I didn't even I I

missed that memo, fortunately.

>> Sorry. I get worked up about this

because there's lots of evidence showing

that first of all it is testosterone.

So even in I'll just go back to the

chimps. The males play more roughly than

the females. In many mammals where there

is a sex difference in play, the males

are playing more roughly. There's a

reason.

>> And and just to make sure people are

following this logic because I there's

one part of the swing we didn't finish.

Okay? Because it's because I keep

interrupting you. So, it's my fault, but

I'm going to do my best to synthesize

this.

>> Bring us back.

>> So,

>> testosterone, you have this real peak

difference in testosterone during a

critical window of development when the

brain is developing. And so, you have a

female brain that is developing in the

absence of testosterone. And you have

>> I wouldn't I just got to pause. We got I

I wouldn't necessarily call it Yeah, I

guess u a female brain because you've

got the the genes. You've also got XY in

every

>> When I say female, I'm just meaning

>> more female t you got a feminized. It's

it's more the XX brain is developing in

the absence of testosterone. The XY

brain is developing in the presence of

high amounts of testosterone.

Testosterone then falls. By the time

these two babies are born, they both

have really low testosterone.

Then it sounds like you're saying

unbeknownst to me until a few minutes

ago, you have this little mini puberty

that comes three months later. How how

high does testosterone get there and

what are the

>> Okay, I want to go back to the critical

period. This is also extremely important

and it's been shown

uh in non-human animals. So there are

the critical period in development.

You've got the period where testosterone

is being produced. um in the fetus and

within that there are

certain developmental periods where

different parts of the brain and body

are receptive to testosterone's actions.

And this is um there are different we

know from um non-human primates that

there are different per critical periods

for say development of the genitalia

other parts of the reproductive system

and potentially for sexual and

aggressive behavior separately. So,

uh that's interesting because

when we want to understand certain

aspects of male behavior or differences

in male behavior, uh it's helpful to

know that possibly

uh aggressive and sexual behavior may

have different thresholds for male

typical versus female typical

>> and that there may be different um

critical periods. So that we don't

really know in humans. Also in males

once you hit your sort of male typical

level of testosterone, we're just

talking about male versus female typical

patterns of behavior. In males there,

it's not really in adulthood at any

stage. There isn't really a dose

response relationship. It's more you're

at a level that's like 10 to 20 times

more than females. female have some

testosterone exposure in uterero and and

some females have more than uh would be

typical and we should talk about that

there there is a dose response

relationship because our levels are so

low and we're extremely sensitive to

differences but males have so much more

those um differences don't seem to make

uh a difference

>> once you cross this threshold.

>> Yes. Yes. Thank you. But I think the

main thing I'm hearing you say, Carol,

is that when you observe

5-year-old boys and 5-year-old girls

behaving completely differently,

the most obvious explanation for the why

is a behavioral difference, not a diff

and the behavioral difference is driven

by potentially the way their brains

developed during that critical window of

being bathed in testosterone as opposed

to the differences in testosterone. one

in a 5-year-old boy versus a 5-year-old

girl, which are dimminimous.

>> Okay, thank you so much.

>> Is that correct?

>> Yes. And thank you for saying it so

clearly because there are some really

important points here.

>> People and and I think what you just

said and what we're going to talk about

in terms of childhood shows that you

cannot judge anyone by their current

testosterone levels. You can't predict

that much.

You can't attribute

uh all variation in behavior and

individual differences in behavior

necessarily to current testosterone

levels. And even within that, if you do

have current levels, um often, yeah, you

can't predict much in terms of say

sexual behavior or aggressive behavior.

You certainly can't with kids because

they don't have any differences. They

hardly have any testosterone at all.

What they do have is on average I I

should have said this before but all of

this is on average there is tremendous

variation. The only thing that

differentiates the sexes cleanly and

essentially is the gameamt the gameamt

production.

>> Define that again because I I want to

make sure the listener understands when

you're referring to gameamt what you're

talking about and the production of them

>> sperm and eggs. So, what road are what

does evolution what has evolution

designed you for? If you're XY and

you're going to be making sperm and that

uh there's going to be a suite of

characteristics

generally that are going to be different

from the suite of characteristics that a

female who has egg who's has ovaries and

eggs will need to maximize reproduction.

So all evolution cares about is how many

uh what portion of your genes are making

it into future generations. So the

design here is about reproductive

strategies that coordinate how your body

grows, what your body is like, what

physical features you develop,

coordinates uh the hormones coordinate

that with certain um patterns of

behavior on average. every all of the

the bodies and the behavior can vary

across XX and XY, but what we're talking

about is these broad patterns mostly to

do with sex and aggression that tend to

differ between males and females. So,

it's really all and this is across

sexually reproducing organisms for the

most part. So, all the other stuff can

vary. It's not that like all XY people

are going to have a higher sex drive and

be some more aggressive. That's just not

the case. It's bodies vary, behavior

varies.

>> I know you weren't consulted during the

design phase, but do you have a sense of

why the female gameamtes are all

produced up front?

>> Oh god.

>> And you you basically get your lot at

birth and then you that's it. It's a

rate of attrition versus why the male

gameamt is just produced on demand.

>> I mean, again, I'm being a bit

facicious. Of course, we don't know

this, but do you do you have an insight

into why that's the case? I

I'm sure there's a better answer, but

here's what I think. And I um

and I hope people will write in with the

better answers.

Making eggs is expensive calorically

and in terms of time and calories, it

they're expensive

and organisms.

So, what we are designed to do is

convert energy into offspring. That's

basically what evolution uh put us here

to do. And you want to do that as

efficiently as possible.

>> So eggs are energetically expensive.

Sperm is less energy energetically

expensive. And I don't know what happens

in terms of how the eggs that go atic.

So we start out with what is it

10 million? I know you just had

>> I know I just talked about this with

Paula. the numbers are sort of

staggering how much attrition there is

between birth and uh

>> so and then you end up at birth you have

1 million and something like that okay

I'm not 100 right yeah

>> but most of them just die so maybe

there's some selection process there

there's an over production and then

because

>> for females there's so much that goes

into the production of each egg and time

and energy and each egg um that you

produce produce is going to limit your

ability. If it takes a long time, that

means you can only have like eight or 10

or however many kids over a lifetime.

Um,

so they're very valuable. So, we're

talking about testes and sperm being

uh testes sort of being not so well

protected, but the eggs are

extraordinarily

well protected if they're um made early

and then just stored.

>> Yeah,

>> I I think and uh that they resume

meiosis of course when when they are

ovulated.

So maybe there's this store and then

there's a selection process that goes on

throughout.

>> That's interesting. I that's a very

interesting idea, right? Which is maybe

you make and let's just pretend we got

these numbers right, but directionally

let's say you make a million, you have

the first 18 years of life or whatever

it is or 16 years of life to select the

best of those. And so it's not a

stochastic process that takes you from

the million to the 10,000 or whatever

the number is. It's truly a winnowing

down of the best of the best of the

best.

>> It could be.

>> Again, this is a teologic BS discussion,

but

>> it is a super interesting question and I

should know uh more about it, but it

does,

>> I think, illustrate the the you know,

the reason why we have different

strategies. It's because

the uh time and energy that females

have to put into reproduction. If say

imagine we're living as hunter

gatherers, there's no birth control.

We're not going through life getting our

periods over and over and going to Whole

Foods and having a job. We're having kid

after kid after kid. We're nursing.

We're, you know, producing the milk with

our own bodies. We have to grow the baby

in an energy relatively energy

restricted environment. The burden for

female mammals, the energetic and time

burden for female mammals is enormous to

produce each offspring. And if you don't

have the right egg or the right sperm,

you you should care about where you're

getting the sperm, then you've lost, you

know, a huge chunk of your potential

reproductive output. Men don't lose a

big chunk of their that just doesn't

happen to them. And this is the you know

sex difference in parental investment

that shapes that's why eggs and sperm

matter in terms of our bodies and our

behaviors because we have to do very

different things and live in different

ways to maximize our reproduction. Okay.

So I wanted to I don't want to get I

want to come back to what you said um

about mini puberty and uh the

differences in hormones. So, I do think

it's the differences in in the increase

in testosterone that males have that

explain

uh why they're more likely to have rough

and tumble play, more energy.

>> And by the way, how high a peak is this

mini puberty and how long does it last?

>> It starts uh within a month after birth,

but then peaks around three months and I

think then goes down until something

like six months. uh

and it appears that it has important

effects on brain development and on the

putting the like lengthening the penis.

So it seems to be an important and

>> but does the female do it as well? In

other words, does the female experience

a rise in estrogen? Yes, there's a a

lower postnatal peak, but the mini

puberty in boys appears to

also be associated with activity levels

in the boys and growth even growth

trajectories. So,

and so that's interesting. Um, but

>> there's a very narrow window of time,

right? Three to six months.

>> Yes. Yes. So in terms of the activity

levels uh you know it could be that that

post-natal

time that that the play in boys is has

something to do with differences in

activity levels, differences in novelty

seeking, different temperament, less uh

fear also. And but if you think about it

from an evolutionary point of view in

male mammals that have to compete for

status and uh operate in a dominance

hierarchy, there's a a lot of male

mammals have dominance hierarchies which

tend to function to reduce aggression

overall because instead of duking it out

every time there's a fertile female or a

delicious piece of fruit in a tree, you

just signal, I'm not going to take your

fruit. I'm subordinate to you. Uh so you

can get along kind of as a group. Yes,

there's there's infighting just like

humans have, but humans have dominance

hierarchies also. And if you don't learn

how to compete physically with other

males as a kid, this has been shown in

in non-human animals and there's some

evidence for this in humans

that uh you have more trouble.

Sorry, it just occurred to me that this

is obviously happening with social

media. People are using their iPhones to

compete instead of getting out in the

yard and play fighting or fighting with

other boys. That's actually healthy

because it ends up reducing aggression.

It it helps especially young boys and

young men learn their place in the

hierarchy, what they're capable of

physically, how to be threatening and

when to be threatening, uh when to

signal that they're submitting. you

know, all of that happens and it's fun.

So, they're driven to do it because it's

adaptive for them evolutionarily. So, I

just wanted to throw that in. And

females tend to have more nurturing

play. I had three older brothers. I was

climbing trees. I was wrestling with

them. But the girls almost never play by

choice just uh with each other. Like,

they don't have a play date where they

just tackling each they're tackling each

other. My son is 16 now. he's still

doing it and he's six feet and his

friends are like one of them is like 62

and it makes me very very nervous. Um

because they can really hurt each other

now. But yeah, they're still doing it.

But

>> yeah, it's it's it's

so it's such a beautiful thing to watch

if you if you just stop judging it for a

moment and just ask yourself the why

question like what is driving this

behavior? Right? Again, for whatever

reasons that are tragic, this has become

a political discussion, but it's really

not. It's simply a discussion of

biology, and it's endlessly fascinating,

right? Like, why is it that when I walk

into the pantry and I see a candy bar

versus a cheese stick or something, I

want to eat the candy bar? Well, that's

evolution. Like I can't I can make a

choice not to do it, but it would be

silly for me not to appreciate how much

my brain looks at the candy bar and sees

the sweetness, the energy density, the

fat, the sugar, and it's like, yeah,

that's what I want. Versus like, you

know, whatever, pick the bland,

healthier option.

>> And similarly, when we watch kids play,

um I find it very interesting. I wasn't

obviously aware of half of what you're

saying, but this idea that um if you let

boys kind of duke it out the way we all

did um

that ultimately it settles them down

again because it's probably too soon to

tell what the results are of the natural

experiment where kids play less. I mean,

we there's certainly no shortage of

discussion about what happens when kids

are all the anxiety and things that come

from endless social media, but this is

kind of a deeper uh and more interesting

question, which is what does it teach us

about aggression uh or lack thereof? And

um I'm I'm curious, have have people

been studying that as closely as they've

been studying the effects of social

media on anxiety and some of

>> I know that there are I'm not sure. um

what the

current literature is on how social

media is affecting play other than it's

not happening as much.

>> Yeah.

>> Which I think is obviously bad. Uh

you're out there, you're being physical,

you're learning about your body, you're

uh

developing relationships with other boys

in particular that are trusting but in

can involve physical aggression. And you

mentioned something about there about um

wanting to have what did you say the

chocolate bar? What was it?

>> Yeah. Yeah. Just like your knee-jerk

reaction is to always eat something

that's sweeter, more calorie dense. Yes.

You know, it's it's

>> okay. So, that's a mis we have a

mismatch. We're designed to be motivated

to seek out these foods and we have to

expend energy to get high calorie foods.

say like we would have maybe gotten

honey and that would have been super

rewarding and we only would have had a

little bit and then we would have ran

around and spent those calories and now

we have you know you can just get your

chocolate bar. So that's a mismatch

situation that's maladaptive.

And

what's interesting is that we've figured

out what to do to some degree with the

male uh any women watching this who are

super competitive and aggressive. That's

a thing, too. It's not that women are

not this way. They certainly are. And I

see more and more examples on my iPhone

from like basketball games and stuff

recently. Um but they're not they tend

to be less physically competitive than

men

>> on average

>> on average. So we have sports that

ritualize this um

motivation or this you know this desire

especially on the part of men and we

have a lot more men who are interested

in watching sports because they're kind

of getting that need met vicariously.

They're like jumping out of their

chairs. often their testosterone is uh

responding also to even the vicarious

participation in sport.

>> Given that we want to um

for the males to get this aggression out

physically,

what do we say about boys that play a

ton of video games and get their

aggression out there? So, you could

argue, well, you know, if they're

playing with their other friends,

they're also, you know, I don't I don't

I don't know enough about video games,

so I'm gonna embarrass myself, but like

I I'm sure there are super aggressive

video games where you're killing each

other and doing something in a virtual

world that you would do if you were, you

know, wrestling. Um, is there a positive

to that? Is there aside from the fact

that they're not getting exercise of

course and not being physically active?

Do we know if that serves as even a

reasonable proxy? I as far as I know

there isn't any getting your aggression

out um getting that need met if it is a

need you know some people don't have

that and in fact most men are not

terribly physically uh aggressive

there's a competitive

uh yeah this is a good question I think

you could sort of compare it to

pornography and ask are men getting out

their sexual need I there's more

evidence that maybe they are getting

some need met there. Uh but in terms of

aggression, I'm not sure

that that it works the same way.

>> So if a parent is listening to this,

is there anything that they should be

concerned about? Um in other words, we

know that all siblings are a little bit

different. So even my two boys are

different. So they're clearly both a

step function more aggressive and

physical than their sister was at a

comparable age, but they're quite

different themselves. The younger one is

a still a step ahead in aggression of

the middle one. That meaning of

>> the younger boy is more aggressive than

the older boy.

>> Can you say what you mean when you say

aggressive?

>> So there's three years between them.

>> Yeah. And

and the obviously the older one is

larger,

the younger one will instigate

physically more.

>> Okay.

>> Right. So if if if if he's unhappy,

>> Yeah. he will attack the the larger

older boy

>> and he doesn't have that same he doesn't

respond maybe even

uh aggressively or

>> well it's you know the the the he he's

just um he just hits not like he'll hit

anything and anyone that stands in his

way whereas the middle one is you know

he's not quite that bad I feel horrible

saying all this stuff my wife's going to

kill me she's like you make them sound

like monsters they're not monsters but

it's like they're just they're boys and

this is boys,

>> but like with with other kids, they're

pretty they're they're more in control,

but with each other, they're they're at

their worst. And which of course I think

is normal for for male siblings. But my

point being is just even between them,

there's quite a difference in

aggression. And maybe it's birth order,

right? Maybe when you're the younger

one, you have to you have to stand your

ground even more.

>> He used to hit my uh older my older

brother, so I was kind of a big hitter

myself. So, so is there anything that I

guess my point is should a parent just

say, "Look, I'm just going to let these

kids do what they're going to do and

understand that there are differences.

Some boys are going to be aggressive,

some are going to be less aggressive,

some are going to play rough, some are

not going to play that rough." Like, are

we is is the best thing you can do as a

parent from from any available evidence

just let them do their thing?

>> So, this is an interesting question. I

hadn't thought about it in this way. So,

I would say the rough play generally if

they're having fun, if they're smiling

and laughing, let them go for it and

don't they need to learn to work their

stuff out and I think the more play the

better and we are designed to play boys

and girls in different ways and it helps

us learn how to be social and have

social relationships and respond

physically and all of that is so

important. important and if we're not

doing that then I think we're going to

have more trouble as adults but when it

gets

uh where it's not so much fun and people

are getting hurt yeah then I think that

the parent has you know

>> so let me let me give you let them work

that out too let me give you a specific

example are boys more likely to bully

than girls

>> I don't think so uh so here's

there there's this difference where boys

will say to your face, you fat f uh you

know, they'll insult you to your face

and bully to your face. Girls are very

aggressive also, but what's interesting

is that they tend not to do it in a

direct confrontational way where they're

exposing themselves as the perpetrator.

Yeah. So they can hide from physical

harm and they c which is adapt more

adaptive but they can denigrate the

reputation say of other girls which they

do because they're their competition in

terms of um mating competition for say

high status males. So they can denigrate

the appearance or behavior especially

sexual behavior and it's cruel. It's

extremely cruel the way that um this

sort of feminine aggression and they

don't have the uh it

>> do we see that kind of behavior amongst

other mammals?

>> Oh, that's a great question.

Well, we certainly see more face-to-face

aggression among male mammals. We do

what? Sorry. What we do see in female

hierarchies sometimes is that there's

harassment

say in um some monkeys there's

harassment of a subordinate female by

the dominant so much so that cortisol

goes up in the one who is being harassed

and the and it interferes with her

capacity to reproduce. So that is uh not

a physical

necessarily confrontation. It's just

harassment. But the uh sex difference in

human aggression with fe with females

doing more of this passive aggression. I

think part of that is that females have

not evolved the same skills to resolve

conflicts so that the hierarchy can sort

of be reinstated. Males can get onto the

basketball, you know, have a pickup game

on the basketball court. It can get

rough. They can insult each other, but

by the end they've sort of worked it

out. Maybe there's a change in the

status hierarchy, but they've worked it

out. It's over. It doesn't go on for

weeks. You don't have to talk about it

endlessly. Females do not have the same

ability to resolve those kinds of

complex social what for us would be very

complex social conflicts. That that is

such an obvious statement the way you

make it for from I mean I I I don't

think of it that way but you I

completely noticed that even thinking

back to high school.

>> Yeah.

>> Like we would as boys get into huge

fights and it would be over by the end

of the day. But there's something

that feels fair about that and to sort

of backstab and not give somebody the

opportunity to and not to be able to

work it out and to gossip about behind

people's backs. So I don't think men

deserve yes more you know out of there's

murder and rape and men are over

represented in those in in horrible

crimes but we shouldn't

glorify you know feminine ways of

interacting necessarily and and try to

get men to be more feminine because

there's a lot of issues also with

typical feminine behavior.

>> So let's talk a little bit about the

pathology though. You just alluded to

it, right? There aren't too many female

murderers and rapists and the the

disproportionate representation of men

in violent crime is, you know, you don't

need statistics to understand that

>> but we definitely do have the statistics

like 95% of murders everywhere are

>> okay

>> male and obviously sexual assault is you

know 98% or something.

>> So what what do what role does

testosterone play in that? So here

again, I think just like with play, uh

people aren't going to like this, but I

want to make sure I so I want to make

sure I I say it clearly. I do think that

the difference, this broad pattern is

similar to what we see in nonhuman

animals where the males are much more

likely to kill each other than the

females. There's many more violent or

aggressive

interactions. So, we have the same like

if you look at both of us, we have

different bodies. You are bigger and

stronger. I started lifting weights

because of you a year ago, so I'm I'm

getting there, but I'll never get to

where you are. Also, I'm older, but um

so physically, men are developed for

competition for ma essentially malemale

competition for mates.

this plays out in this destructive way

in in society. Um, and so I'm I I

believe that the ultimate reason for the

difference is testosterone.

Uh,

however,

the uh crime say the murder rates in

Canada,

men are committing, you know, fewer

murders in Canada than they are in the

US. We can't attribute that to

testosterone levels.

>> So that's not because of differences in

testosterone level.

>> It is because socialization and culture,

religion, the laws uh you know all have

a huge impact on what the values are in

any particular society, what is

tolerated, what is encouraged. Some

societies basically allow men to beat

and rape their wives, right? So it's so

you have higher rates of those male

behaviors where it's not tolerated and

the culture is totally different. You

have lower rates of those behaviors, but

everywhere

>> you're you will have the sex difference

with all of these behaviors higher in

men. Uh, so

I'm glad you asked this because the re I

think the main reason people don't like

biological explanations for sex

differences is is because they

misinterpret

uh a tendency or a predisposition

for a behavior or um

or a biological explanation as

suggesting that it's impossible to

change behavior. It's not uh you know

that there's no variation across the

sexes in behavior. there is and just

because there might be a biological

explanation or even a a genetic

explanation

uh

the important thing to remember is that

we develop within an environment every

you know it's gene environment

interactions we develop within a society

and how we develop

and even how our hormones say respond to

different kinds of interactions is

impacted by the social system and and by

the ecology and everything else. So it's

complicated. Um but yeah, I think that

the re the ultimate reason is is because

of gen the genetic difference which is

the Y chromosome and the hormones that

it hormonal differences that it leads

to. And I, you know, we haven't talked

about female behavior, but of course,

nurturing, if you're going to be growing

and producing and holding and feeding

and caring for a baby, and you're the

one who absolutely has to do it, and

that's the female. Of course, we get

help from men. Um, and sometimes men

even take over as the uh primary

caregivers, which is extremely unusual

in animals uh in mammals. But so men are

capable of all of that nurturing if the

society values it because some societies

don't value that and then they're still

capable but they're not apt to do that.

Uh but so for females it just doesn't

pay reproductively

in general to be super aggressive. We

need our bodies to be healthy and we

have to live a long life. So the longer

our lives, the longer our reproductive

output. Men can live short uh you know

die young and have great reproductive

success. Yes. If they take risks and

physical risks and that just doesn't

have the same payoff for females. There

are some uh primates for instance where

the females are you know relatively

aggressive but it's almost never to the

same extent um as males. It's so

interesting when you think about

how as humans, right, like we we hold

ourselves to a higher standard than we

would hold animals, right? And and and

look, but I'll give you I'll give you a

very concrete example. Okay? So,

>> if we go back in time 500 years, first

of all, neither of us would be alive.

So, let's forget that part of the

discussion. But let's just say 500 years

ago, if you had a male that was 25 years

old, he would readily reproduce with a

14year-old female, right? That would be

completely normal and evolutionary

evolutionarily wise.

But we've made a decision, at least in

our society, that that's unacceptable.

>> And I think most people think that

that's a good decision, right?

>> Yeah. So that's an example of we have

made a societal norm that says it's

unacceptable for a 14-year-old girl to

be reproducing um certainly at the hands

of an older man. So if she gets pregnant

from her 14-year-old boyfriend, we

that's a different discussion and we can

help them both out. But

>> in this country anyway. Yeah. My point

of the story is we've made a decision

that this is no longer acceptable. Just

as we've made a decision that a husband

can't rape his wife, we have just

decided that that's not, you know, maybe

that was cool 200 years ago, it's not

cool today.

>> Yeah.

>> So to play the other side of some of

these arguments, right? Is there someone

watching us who's saying, "Peter, Carol,

you guys are talking about all this

aggression stuff, but we're humans

living in the 21st century, like we have

to change. We have to evolve as a

species. Is there a case to be made that

men should be less aggressive because

all of these evolutionary reasons that

you described aren't as necessary? Women

and men are going to live through their

evolutionary uh pardon me, their

reproductive lives. We don't have this

urgency. We don't need this competition.

Again, I'm not saying I agree with that

or anything, but I'm just saying like

there there's a steel man for the other

side of this, just as in those extreme

examples of we don't have sex with 14y

olds and we don't rape our wives.

>> So, what would it take for you to not

eat that chocolate?

>> Well, it's interesting, right? Food is a

really tough one, isn't it? Um, it can

be done. It just takes a ton of

willpower. That's the truth. I think it

can be. So the food is a great way to

think about it. There's food and sex. Uh

and aggression is for ultimately in a

way for sex.

>> Yeah. Well, I mean for both Yes. But

people will

>> Yes. Yeah.

>> Um so for men more than women,

aggression is certainly more about

>> but like to to play off that I don't

need to be an alpha male to get as much

food as I need today. Like,

>> but you are an alpha male and you have a

lot of food and you have like you

>> but I don't need we don't need to be an

alpha male to get food.

>> No, that's right.

>> That's my point. Today I don't

>> So you're saying we should get rid of

the drive. Okay. I'm not saying I I'm

just exploring this idea exploring

because I think so there's physical

competition which we certainly do not

need

>> but think about what we get from the

male. So there is a sex difference in

certain drives. Uh men tend to be more

sort of

driven to achieve specific and more

narrow goals and like hyperfocused on

certain goals and to achieve via you

know um

to be the top of the heap in in one

thing like chess. I wrote some article

on sex differences in chess and learned

a lot about, you know, cuz I was like,

what? Why are men consistently better at

chess than women? And they are.

>> No, no, I'm only laughing. If you only

knew of the of the rabbit hole, we could

go down on that front, but I'm going to

refrain.

>> So, I'm really interested in that. and

what and I had what I suspected was not

uh appears not to be the case in terms

of it's not doesn't seem to be explained

by differences in cognition at least

that's not necessarily the driving force

what is the I think the driving force is

that men boys and men are much more

willing to spend countless hours

studying the moves and practicing and

seeing their coach and you know trying

to beat their competition. And for

women, like there are other things to do

that matter in their lives more. They're

just certainly there are some women who

do who do that kind of focus, but there

are way more men. And I'm saying this

because

there's that competitive drive. chess. I

don't know what we're like getting out

of that, but uh

>> You haven't played, have you?

>> No, I have.

>> You have? Okay. All right.

>> And not super seriously, but my son was

really into it for a while. My my

brother I I know a lot of people who are

>> obsessed with it. Um but when I say what

we're getting, I mean so socially. So

competitive men super and people I'm not

again I want to I'm not saying that

women are not competitive or haven't

made incredible adv you know social

advances in all kinds of domains but

what I am saying is that if we want to

interfere with the male desire to

compete we are also interfering with

whatever products we get or advances we

get from that intense drive in Being in

academia as I was you know for 25 years

there's a lot that's that is produced

because people want to be first. They

want to nail finding this gene or be the