#374 - The evolutionary biology of testosterone: how it shapes male development and sex-based behavioral differences, | Carole Hooven, Ph.D.

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Dec 1, 2025

Carole Hooven, a human evolutionary biologist and former Harvard lecturer, dives deep into the fascinating world of testosterone and its impact on male development and behavior. She explains how prenatal testosterone influences brain development and lifelong behavioral patterns, highlighting unique aggression styles and play behaviors. Carole shares insights on the implications of modern society on male aggression, the necessity of testosterone therapy, and her own experience with hormone therapy. She also discusses her upcoming book on masculinity and cultural narratives.

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INSIGHT

Testosterone As A Cross‑Species Mechanism

Testosterone links human and non-human male behavior and offers a proximate mechanism for sex differences.
Evolutionary pressures from sperm vs egg production shape broad patterns in bodies and behaviors.

INSIGHT

SRY Triggers Male Gonadal Differentiation

The SRY gene on the Y chromosome triggers undifferentiated gonads to form testes, changing developmental trajectories.
Without SRY expression, the gonad actively differentiates toward ovaries rather than passively staying female.

INSIGHT

DHT Masculinizes External Genitalia

5α‑reductase converts testosterone to locally potent DHT in genital tissue to masculinize external genitalia.
Individuals with 5α‑reductase deficiency show typical male bodies but feminized external genitalia until puberty.

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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.

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