The Peter Attia Drive
#374 - The evolutionary biology of testosterone: how it shapes male development and sex-based behavioral differences, | Carole Hooven, Ph.D.
01 Dec 2025
View the Show Notes Page for This Episode Become a Member to Receive Exclusive Content Sign Up to Receive Peter's Weekly Newsletter Carole Hooven is a human evolutionary biologist whose research centers on testosterone, sex differences, and behavior. In this episode, she explores how prenatal testosterone orchestrates male development in the body and brain, how early hormonal surges shape lifelong behavioral tendencies, and what rare natural experiments—such as 5-alpha-reductase deficiency—reveal about the biology of sex differentiation. She discusses distinct male and female aggression styles through an evolutionary lens, how modern environments interact with ancient competitive drives, and the implications of attempting to suppress them. The conversation also covers testosterone across the lifespan, the role of hormone therapy in both men and women, and Carole's own experience after surgical menopause, culminating in a broader discussion of masculinity, cultural narratives, and the consequences of denying biological sex differences. We discuss: How Carole became interested in exploring the biological and evolutionary roots of sex differences and the role of testosterone [2:30]; How testosterone and other hormones influence sex differences in aggression and behavior across species [9:45]; How chromosomes, the SRY gene, and early hormones direct embryonic sexual differentiation [12:15]; A stark contrast of male social bonding compared to females, and evolutionary parallels in chimpanzees [19:30]; How hormones like DHT shape sexual differentiation, and how 5⍺-reductase deficiency reveals the distinct roles of these hormones [22:45]; How sex chromosomes and prenatal testosterone shape early brain development and explain sex differences in childhood behavior [31:30]; How gamete differences shape reproductive strategies, energetic costs, and sex-specific behavior [42:30]; How evolutionary biology shapes sex differences in play, aggression, and conflict resolution (and how modern environments and cultural messaging can disrupt those patterns) [49:00]; Why males commit disproportionately more violent crime, and how cultural and environmental forces shape aggression [1:01:00]; Why females evolved different behavioral strategies: nurturing, risk aversion, and the cultural norms that override biology [1:04:00]; Whether male aggression is still necessary in modern society, why the underlying biological drives persist, and how modern society redirects these drives [1:06:30]; How testosterone levels naturally shift to support fatherhood and caregiving [1:13:30]; How testosterone shapes male mating strategies, and why long-term pair-bonding persists even when reproduction is no longer at stake [1:18:30]; The distinct roles of estrogen in male development, mood, libido, and muscle [1:25:00]; How evolution, health, lifestyle, and androgen receptor biology shape modern testosterone replacement therapy (TRT) [1:34:15]; Carole's experience with hormone replacement therapy (HRT), and the risks associated with TRT in younger men [1:45:15]; How Carole rebuilt after controversy: leaving academia and recommitting to scientific honesty [1:51:30,]; Carole's next book: examining masculinity, cultural narratives, and the cost of denying biological sex differences [1:57:30]; and More. Connect With Peter on Twitter, Instagram, Facebook and YouTube
Chapter 1: What is discussed at the start of this section?
Hey, everyone. Welcome to The Drive Podcast. I'm your host, Peter Attia. This podcast, my website, and my weekly newsletter all focus on the goal of translating the science of longevity into something accessible for everyone. Our goal is to provide the best content in health and wellness, and we've established a great team of analysts to make this happen.
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If you want to take your knowledge of this space to the next level, it's our goal to ensure members get back much more than the price of a subscription. If you want to learn more about the benefits of our premium membership, head over to peteratiamd.com forward slash subscribe. My guest this week is Carol Hoeven.
Carol is a human evolutionary biologist, a former Harvard lecturer, and non-resident senior fellow at the American Enterprise Institute. Her research focuses on testosterone, sex differences, and behavior. She holds a PhD in biological anthropology, now human evolutionary biology, from Harvard University, and is the author of T, The Story of Testosterone, The Hormone That Dominates and Divides Us.
In this episode, we discuss how prenatal testosterone shapes the male body and brain, turning genetic signals into thousands of developmental changes that underlie later sex differences, critical hormone surges and why they matter for lifelong behavior.
DHT, androgen receptors, and rare natural experiments, for example 5-alpha reductase deficiency, that reveal how external genitalia and the prostate masculinize, distinct male and female aggression styles, direct physical confrontation versus indirect or relational tactics, and the evolutionary logic behind each, why modern life changes but doesn't erase ancient drives like male competitiveness and the trade-offs of trying to suppress them.
testosterone, aging, and hormone therapy for both sexes, including Carol's personal experience after surgical menopause, and the cultural debate over masculinity and the cost of denying biological sex differences, a theme of Carol's forthcoming book. So without further delay, please enjoy my conversation with Carol Hoeven. Carol, thank you so much for coming out to Austin.
Great to meet you in person.
Thank you so much for having me. I'm thrilled to be here.
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Chapter 2: How does Carole Hooven's background influence her research on testosterone?
Some of that was my fault for not understanding the culture well enough and what I was getting into. 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 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 to Harvard to try to do a graduate degree where I could do more to understand the evolutionary basis of human behavior. I ended up
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 to believe that most human sex differences are cultural.
Or if you think that they're not, it's better you don't say that out loud to too many people or in the wrong place. So when I spent time with the chimps, I was really blown away by the ways that 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, 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 not just the ability to produce sperm or eggs, but kind of the way that the organism is designed and the 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 got interested in testosterone because this is one thing I could grab onto that links very clearly humans, chimpanzees, every other mammal in terms of males having much higher levels than females. And it's not just mammals. There are other forms
of steroid hormones that other species have, but this is pervasive and just a very powerful way to understand proximately, that means what's happening 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 up reapplying to Harvard and getting into the grad program there. And I did my dissertation on testosterone and sex differences in cognition.
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Chapter 3: What role does testosterone play in male behavioral differences?
the way we think and process information and I had men watch sexy videos and also videos of dental surgery and collected their saliva and measured their testosterone in the lab and then I just stayed on at Harvard mostly just teaching.
I want to go back to something you said a second ago, which is the distinction between mammals and non-mammals. And I never really thought of it until you said this. But if I were to look at 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 hormone?
So 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, 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. First of all, 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 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 an interesting way to understand some male competitive strategies. But generally, when... In the species, if the female is just as aggressive, often it's maternal aggression and not necessarily mate competition. Maternal aggression tends to be mediated more by estrogen than testosterone, even in hyenas, 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. And that seems not to be mediated in the adult, at least by comparable levels of testosterone. There seems to be potentially something going on in early development.
But I don't know of good evidence that testosterone acts similarly in females to mediate, say, aggression. We'll say mating aggression.
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?
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Chapter 4: How does testosterone affect aggression and social dynamics in males?
Yes, yes, exactly. I just want to start with, let's get through the first nine months and then let's help understand how 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 heterozygotic chromosomes. So there's temperature-dependent sex determination.
So people should not confuse the sex hormones themselves with the definition of sex.
Chromosomes are the sex hormones.
Sorry, chromosomes. Thank you. In mammals, the chromosomes determine sex, but do not define sex. Again, across almost all sexually reproducing organisms, it's the gamete type that the organism is basically designed around, that the reproductive system is designed around, that defines sex.
Other organisms can be hermaphroditic, produce both gamete types at the same time, or they can be sequential hermaphrodites. So I just want to get that out first. So in humans, the mother's egg, the sex chromosome is always going to be an X that it donates 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 an X. in general. Those two combine and the developing embryo is going to be either XX and XY. So let's just start with the XY. So you were an XY.
I had a son who was an XY, which is weird for women because they will have something inside of them that has testicles that produce testosterone, which I think is interesting. So an XY fetus around five or six weeks. I should just say that XX and XY are both, 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 gene. 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 either one.
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Chapter 5: What drives male aggression and how does it relate to testosterone?
What would it take for you to not eat that chocolate?
Well, it's interesting. Food is a really tough one, isn't it? It can be done. It just takes a ton of willpower.
Food is a great way to think about it. There's food and sex and aggression is for ultimately in a way for sex.
Yeah. Well, I mean, for both.
Yes. For men more than women, aggression is certainly more about.
To play off that, I don't need to be an alpha male to get as much food as I need today.
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Chapter 6: How do testosterone levels influence fatherhood and caregiving?
But you are an alpha male and you have a lot of food. But I don't need to be.
We don't need to be an alpha male to get food.
No, that's right.
That's my point.
So you're saying we should get rid of the drive.
I'm just exploring this idea.
Because there's physical competition, which we certainly do not need. But think about what we get from the male.
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Chapter 7: What are the implications of testosterone replacement therapy?
So there is a sex difference in certain drives. Men tend to be more driven to achieve specific and more narrow goals and like hyper-focused on certain goals and to achieve, to be the top of the heap in one thing. Chess, I wrote some article on sex differences in chess and learned a lot because I was like, why are men consistently better at chess than women? And they are.
If you only knew of the rabbit hole, we could go down on that front, but I'm going to refrain.
Okay, so I'm really interested in that. And what I suspected appears not to be the case in terms of doesn't seem to be explained by differences in cognition. At least that's not necessarily the driving force. What is, I think, the driving force is that boys and men are much more willing to spend
Chapter 8: How does Carole Hooven view the cultural narrative around masculinity?
countless hours studying the moves and practicing and seeing their coach and trying to beat their competition. And for women, there are other things to do that matter in their lives more. Certainly there are some women who do that kind of focus, but there are way more men. I'm saying this because that competitive drive, chess, I don't know what we're like getting out of that,
You haven't played, have you?
No, I have.
You have?
Okay. Yes. I'm not super seriously, but my son was really into it for a while. My brother, I know a lot of people who are obsessed with it. But when I say what we're getting, I mean socially. Competitive men, I'm not saying that women are not competitive or haven't made incredible 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. Being in academia, as I was for 25 years, There's a lot that is produced because people want to be first. They want to nail finding this gene or be the first to make a certain discovery.
It's tremendously productive often, that insane drive that men have. And I think women have less of it because we have kids. We are designed to have the kids. We don't have the same, I must do something else, have to produce this other thing with the same drive. Again, there's tons of variation here. There's tons of crossover. This is just a pattern.
I think men have more of that, potentially because they're not designed to have kids, to produce them with their own bodies.
Let me play back to you what I think I'm hearing and with a little bit of- I'm in trouble.
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