Steve Stewart-Williams warns that denying sex differences backfires on health

Why does discussing the biological and evolutionary differences between men and women feel like stepping onto a conversational landmine? As a psychologist, I often sit with people who are deeply afraid of what their own biology might say about them. We worry that looking too closely at our evolutionary heritage will lock us into cages of historical sexism. It is easy to understand why. For centuries, bad science served as a tool to keep women small. In the late 1800s, scientists like Gustave Le Bon claimed intellectually accomplished women were as rare as two-headed gorillas. With a history that messy, feeling nervous about the biology of sex differences is a completely natural defense mechanism.

But avoiding the conversation does not protect us. Real growth happens when we face reality with radical honesty and deep self-compassion. Avoiding the science of sex differences out of fear does not prevent discrimination; instead, it leaves us blind to the actual mechanisms that drive our behavior. During a profound, long-form discussion on Modern Wisdom hosted by Chris Williamson, evolutionary psychologist Steve Stewart-Williams, author of The Ape That Understood the Universe, laid out a compelling case for why studying our evolved nature is the ultimate antidote to historical prejudice, rather than its continuation.

When we understand the "why" behind our baseline tendencies, we can stop judging ourselves for having them. Understanding our ancestral programming is not about giving ourselves an excuse to behave badly. It is about acquiring the self-awareness needed to step out of reactive patterns and make conscious, intentional choices. Growth begins the moment we stop fighting our nature and start understanding it.

The Biological Anchor of Gamete Size

Before exploring complex psychological behaviors, we must anchor ourselves in biological reality. What is biological sex? In recent years, public debates have clouded this fundamental question, yet science offers a beautifully simple, elegant definition. Across the entire tree of sexually reproducing life, biological sex is defined by gamete size.

This is a universal truth of biology. Males produce the smaller, highly mobile gametes called sperm. Females produce the larger, nutrient-rich gametes called eggs. There is no third gamete size. This biological setup, known as anisogamy, evolved from an ancient state where all gametes were the same size. That uniform state was evolutionary unstable.

Imagine a prehistoric biological landscape where organisms produced identical gametes. Over time, natural selection pushed this system in two opposite directions. Some organisms began packing extra resources into their gametes to help the resulting offspring survive. These gametes became larger, heavier, and less mobile. Simultaneously, other organisms began producing tiny, stripped-down gametes designed for speed and numbers. These smaller gametes traveled light, seeking out the resource-rich larger gametes to ride on their coattails.

In this evolutionary transition, the middle of the barbell became a dead zone. Medium-sized gametes were too slow to compete with the small ones and lacked the survival provisions of the large ones. This pressure pushed the system into a clean binary. Today, this binary remains the foundation of sexual reproduction in almost every animal and plant species on Earth.

While there is immense physical and psychological variation within each sex, the underlying biological anchor remains steadfast. Recognizing this simple physical reality is not about limiting human potential. Rather, it provides a stable starting point from which we can explore the magnificent variety of human nature.

The Six Pillars of Unlearned Behavior

How do we know our psychological differences are not merely the products of social conditioning? Many theorists argue that culture alone carves the differences we observe between men and women. While socialization plays a major role in shaping how traits are expressed, a wealth of evidence suggests a powerful, unlearned biological contribution underpins our psychology. Stewart-Williams outlines six distinct lines of evidence that point to these innate drives.

Early Lifespan Appearance

Many key sex differences show up long before cultural conditioning has time to take deep root. Consider risk-taking and physical aggression. As soon as toddlers are mobile, boys are consistently more likely than girls to end up in the emergency room due to high-risk physical play. This difference is not taught; it is a baseline behavioral urge that manifests as soon as the physical body is capable of executing it.

Persistence Across Cultural Pressure

When we look at the historical record, certain differences persist even in the face of active social discouragement. For instance, most modern cultures actively try to suppress young male aggression and violence. Parents, teachers, and law enforcement expend vast energy trying to keep this behavior in check. Yet, despite massive cultural pressure to suppress it, male physical aggression rises sharply during puberty across every studied society.

Cross-Cultural Universality

If culture were the sole author of sex differences, we would expect to find matriarchal, highly peaceful societies where women commit the vast majority of violent crimes, or societies where women do not participate in childcare. We do not. In every single nation on Earth where data is collected, young men commit over ninety percent of homicides. Similarly, women across all cultures participate more heavily in direct infant care. The consistency across vastly different ecological and social systems points to a shared evolutionary template.

Hormonal Correlates

Our psychological profiles track our prenatal and active hormonal exposures. A stark example of this is found in girls born with Congenital Adrenal Hyperplasia (CAH), a genetic condition that exposes developing female fetuses to high levels of male hormones in the womb. Later in life, CAH girls consistently show a strong preference for male-typical toys, a reduced interest in marriage and childcare, and a significantly higher likelihood of entering things-oriented professions. Their psychological preferences shift toward the male average because of early biological exposure, independent of how they are socialized.

The Animal Kingdom Mirror

We do not exist in a biological vacuum. Many of our behavioral differences mirror those of other species that faced similar evolutionary pressures. The sex split in lethal aggression is not unique to humans. In chimpanzees, males perpetrate approximately ninety-two percent of intra-species killings, a figure almost identical to the ninety-five percent statistic observed in humans. When we see our deepest behavioral patterns reflected in our closest living relatives, attributing those patterns purely to modern marketing or social norms becomes untenable.

Long-Term Historical Stability

Despite massive shifts in social roles over the last century, basic psychological differences have remained remarkably stable. Measurements of career interests, mate preferences, and personality traits have shown minimal shifts in their average differences since psychologists first began systematically tracking them in the early 1900s. The surface of culture changes rapidly, but the deep currents of human nature remain remarkably consistent.

The Gender Equality Paradox

Perhaps the most fascinating and counterintuitive finding in modern social science is the Gender Equality Paradox. For decades, social roles theorists argued that if we could build a society with perfect gender equality, the psychological differences between men and women would naturally evaporate. This seemed like a logical prediction. If social conditioning is the sole cause of these differences, removing the conditioning should remove the differences.

But when progressive nations in Scandinavia began implementing deep, systemic changes to promote gender equality, the exact opposite happened. In countries like Sweden and Norway, the psychological gaps between men and women grew larger, not smaller.

In these highly egalitarian societies, women became even less likely to enter engineering and computer science fields, and men became even more likely to choose technical paths. Personality differences in traits like empathy, assertiveness, and neuroticism expanded to their largest recorded levels. Why?

An evolutionary lens explains this beautifully. When a society is poor or restrictive, survival dictates people's choices. A young woman in a developing nation might major in engineering because it is her only ticket to financial stability, regardless of her personal interests. But when you build a wealthy, highly equal society, you remove those economic constraints. You create a safe environment where people are free to do whatever they genuinely want to do.

When you give people total freedom of choice, they do not choose to be identical. Instead, they choose to express their baseline, evolved preferences. Removing social constraints allows our biological differences to bloom fully. This is a liberating truth. It means that the presence of gender gaps in choice-driven fields is not necessarily a sign of systemic oppression; it can be a sign of a healthy, free society.

As a coach, this is where I find the most powerful lesson. We must watch out for "the soft bigotry of male expectations." This is the subconscious belief that the male standard of behavior—striving for high-paying technical jobs, working eighty-hour weeks, and focusing on things over people—is the gold standard of human achievement. When we push women to be exactly like men, we are implicitly devaluing traditionally female-typical preferences, such as prioritizing family, deep human connection, and people-oriented careers. True equality is not about forcing everyone into a single, unisex mold. True equality is about letting people be themselves, without judgment.

Mating, Risk, and the Ultimate Cost of Survival

To understand why these psychological differences developed, we must look at the concepts of parental investment and reproductive variance. In any species, the sex that invests more in producing and rearing offspring is naturally more selective when choosing mates. For human females, the biological cost of reproduction is extraordinarily high, requiring nine months of pregnancy, childbirth, and lactation.

For an ancestral male, the minimum investment required to reproduce was a single physical act. This biological asymmetry created vastly different reproductive limits. A male could potentially father hundreds of children, while a female was limited to a much smaller number of offspring over her lifespan.

This difference in reproductive variance meant that for males, the stakes of the mating game were incredibly high. A successful ancestral male could pass on his genes in massive numbers, while an unsuccessful male faced total genetic extinction. This high-variance environment selected for males who were willing to take extreme physical risks, demonstrate intense competitiveness, and engage in physical aggression to climb the social hierarchy.

This ancestral risk-taking behavior cuts both ways. Young men are vastly overrepresented among those who commit stupid, self-inflicted acts of fatal stupidity. Yet, they are also vastly overrepresented among those who perform extraordinary acts of heroic self-sacrifice to save strangers. It is the same evolved psychological mechanism—a willingness to take extreme physical risks—expressing itself in different environments.

Understanding this evolutionary background helps us look at modern relationship struggles with deeper empathy. When we see differences in interest in casual sex, visual sexual triggers, or patterns of relationship jealousy, we can see them as ancient survival strategies, rather than personal failures. Men's jealousy is historically more focused on sexual fidelity due to the ancient threat of raising another man's child. Women's jealousy is historically more focused on emotional commitment because a partner's emotional desertion threatened her physical survival and that of her offspring.

When we understand these gut reactions as ancient programming, we can stop letting them run our lives. We can validate the feeling without blindly reacting to it. Self-awareness is the bridge that allows us to move from unconscious evolutionary reaction to conscious personal choice.

The Threat of Denying Our True Nature

What happens when we deny these differences? In our well-intentioned quest for equality, we often try to force a narrative of total sameness. But denying the biological reality of sex differences has severe, real-world consequences, particularly in mental and physical healthcare.

When we pretend men and women are identical, we overlook sex-specific presentations of critical health issues. For example, cardiovascular disease presents differently in women than in men. While men often experience classic shooting pains down the arm, women are much more likely to experience shortness of breath. Because the historical medical standard was based on the male average, women's heart attacks are frequently missed.

Similarly, developmental conditions like autism present differently in girls, often lacking the repetitive physical behaviors commonly seen in boys. If we ignore these differences, girls with autism go undiagnosed and do not get the support they need. In mental health, the high rate of depression in women is widely recognized, but this can lead clinicians to overlook clinical depression in men, who may express their distress through irritability or risk-taking rather than sadness.

On a social level, denying our differences creates deep, unnecessary resentment. If we assume that any gap in career representation is proof of active sexism, we end up implementing highly coercive, top-down social engineering. This does not fix discrimination; it simply breeds resentment, pushes people into roles they do not want, and fractures our social cohesion.

My coaching philosophy is simple: let people be themselves. If someone's path aligns with traditional gender roles, that is wonderful. If their path is completely non-traditional, that is equally wonderful. Our goal should not be to enforce identical outcomes, but to remove all barriers, eliminate bias, and respect the unique choices of every individual.

True growth happens one intentional step at a time. By embracing the fascinating, complex science of our evolved nature, we can stop fighting our biology and start working with it. When we replace fear with curiosity, we can build a world where men and women are both understood, deeply respected, and free to achieve their true potential.