Editorial note: The answers are editorial distillations based on the interview and on his book A Billion Years of Sex Differences.
Does evolutionary psychology say that behaviour is biologically fixed?
No. An evolutionary origin does not necessarily mean a trait is fixed forever. Genes may push development in certain directions, but they are not the only influences. Learning, culture, incentives, and institutions also matter. The claim is not that biology alone is destiny. The claim is that biology is part of the causal story.
Does explaining a behaviour excuse it?
No. Explanation and justification are different things. Evolutionary psychology may help explain sex differences in aggression, jealousy, sexual behaviour, and parental care. But an explanation does not tell us whether a behaviour or sex difference is morally desirable. “Natural” does not necessarily mean “good.” Why would it?
Are most psychological sex differences huge?
No. In our species, at least, most psychological sex differences are statistical differences with substantial overlap. Men and women may differ on average, but many women score higher than many men on so-called male-typical traits, and many men score higher than many women on so-called female-typical traits. Average differences are not rules about individuals.
What is a “fuzzy” sex difference?
A fuzzy or statistical sex difference is a difference in group averages, not a clean division. For example, one sex may have a higher average on a trait, while the two distributions still overlap heavily. Most human sex differences fall into this category, rather than into a simple “men are like this, women are like that” pattern – or even a “most men are like this, most women are like that” pattern.
What kinds of sex differences does the book discuss?
The book discusses physical, developmental, psychological, behavioural, and mental-health sex differences. Examples include differences in size and strength, the timing of puberty, life expectancy, sexual orientation, interest in casual sex, mate preferences, aggression, risk-taking, childcare, things-oriented versus people-oriented interests, spatial versus verbal abilities, childhood play and toy preferences, ADHD, autism, substance abuse, depression, anxiety, and eating disorders.
Are evolutionary-psychology hypotheses unfalsifiable?
No. This is a common misconception. Evolutionary hypotheses are falsifiable, and many have been falsified, including some of Stewart-Williams’s own hypotheses.
What is one example of a falsified evolutionary hypothesis?
One example discussed in the interview is E. O. Wilson’s kin-selection hypothesis about same-sex sexual orientation. The idea was that people with a same-sex orientation help boost their relatives’ reproductive success, rather than their own, thus indirectly passing on the genes giving rise to their sexual orientation through the relatives. Researchers tested the idea, and the verdict is that it does not seem to explain same-sex sexual orientation in humans.
What about the ovulatory-shift or “good genes” hypothesis?
The dual-mating or ovulatory-shift hypothesis holds that women sometimes seek investment from one kind of man and “good genes” from another, with preferences shifting around ovulation. In the interview, Stewart-Williams called it an interesting hypothesis and said the debate is not completely closed. But he also said he currently is much more persuaded by critics who argue that the evidence has not borne it out.
Does socialisation explain sex differences?
It explains some things, but not everything. Socialisation clearly matters, as do stereotypes and culture. But it is not sufficient as a complete explanation. Several points count against nurture-only accounts: some differences appear early in development or in the wake of puberty; many appear across cultures; some are linked to prenatal hormones; some resemble patterns in other species; and some grow rather than shrink in more gender-equal countries.
What is the gender-equality paradox?
The gender-equality paradox is the finding that many sex differences are larger, not smaller, in wealthier, more individualistic, more gender-equal countries. Stewart-Williams treats this as a problem for simple patriarchy explanations or explanations based on societal sex roles.
Are stereotypes always false?
No. Following Lee Jussim, Stewart-Williams argues that stereotypes can sometimes track social reality. That does not mean stereotypes are always accurate, harmless, or morally acceptable. They can exaggerate or minimize differences, become self-fulfilling to some degree, or encourage unfair treatment of individuals. But the mere fact that a belief is a stereotype does not prove that it is false.
Can acknowledging average differences reduce stereotyping?
Possibly. Nikil Mukerji raised the point that stating average differences need not always make people conform to them. It could sometimes have the opposite effect: if people know the average tendency, they may consciously decide not to follow it. Stewart-Williams accepted the possibility. The responsible position is to acknowledge average differences while encouraging individuality.
How can denying sex differences harm mental health care?
If sex differences in psychological disorders are ignored, clinicians and ordinary people may miss problems in the less affected sex. In the interview and the book, examples include ADHD and autism, which may be overlooked in girls because the standard descriptions of these disorders fit boys better (autism less often involves repetitive behaviour in girls, for instance). Another example is depression, which may be overlooked in men because the standard description fits women better (in men, depression more often involves anger, aggression, or substance use, for example).
How can denying sex differences distort public policy?
If average differences in interests are ignored, occupational gaps may be treated as if they were entirely caused by discrimination. Stewart-Williams argues that this can misdirect resources, create resentment, and justify coercive policies. Bias exists, but it is rarely the whole explanation. A good policy diagnosis has to ask how much of a gap is due to bias, how much to interests and lifestyle preferences, and how much to other factors.
Does affirmative action have possible costs?
Stewart-Williams argues that it can. If positions are reserved for one sex, or if a less qualified candidate is chosen to achieve numerical parity, the policy may reverse discrimination rather than eliminate it. It may also cast doubt on the competence of the supposedly benefited group and increase impostor feelings among beneficiaries. This is presented as a risk of some policies, not as a claim that every affirmative-action policy is unjustified.
What does “sex” mean biologically?
In the book, Stewart-Williams uses the gamete definition, which has been the standard scientific definition since the late 1800s. Females are organised around the production of large gametes, eggs; males are organised around the production of small gametes, sperm. Chromosomes, genitals, hormones, and secondary sex traits are connected to sex, but they do not define it.
Why be skeptical of the term “gender”?
Because it has too many meanings. Sometimes it means sex. Sometimes it means masculinity or femininity. Sometimes it means social roles, stereotypes, gender identity, personality profiles, or differences supposedly caused by nurture. Stewart-Williams argues that this ambiguity makes the term less useful for science. If one means sex, one should say sex. If one means personality, one should say personality. If one means social roles, one should say social roles. In addition, many definitions of gender have serious problems of their own.
What is the responsible position on sex differences?
The responsible position is neither denial nor exaggeration. Stewart-Williams argues for telling the truth carefully: acknowledge average differences where the evidence supports them; emphasise overlap and individuality; reject the naturalistic fallacy; avoid treating averages as prescriptions; and give every individual a fair chance.