Mars and Venus revisited: How deep do sex differences go?
“Vive la différence,” the French say, and they seem to know what they're talking about. But when the rest of us describe human beings as being male and female - masculine and feminine - what are we really referring to? For a long time, the matter seemed to be settled. Every college course on gender and Women’s Studies I ever took was premised on Simone de Beauvoir’s mantra from her book The Second Sex (1949) that “One is not born, but rather becomes, a woman” (and a man too, for that matter). The notion that perceived sex differences are products of nurture and not nature flew in the face of most common wisdom up to that point, and is still unfamiliar to most people today, at least if we go by the extraordinary success of authors like John Gray and Alan and Barbara Pease with their books on why women “can’t park” and men “can’t talk.”
In the so-called developed countries, however, “gender” – i.e., the general notion that, when it comes to behavioral differences between men and women, sociocultural identity formation trumps biological differences – has become the common currency of academia and politics. Biologists and developmental scientists have been increasingly going the same route ever since the early twentieth century. In 2005, psychologist Janet Shibley Hyde summed up much of the research in an article entitled “The Gender Similarities Hypothesis,” in which she stated that
males and females are similar on most, but not all, psychological variables. That is, men and women, as well as boys and girls, are more alike than they are different. In terms of effect sizes, ... most psychological gender differences are in the close-to- zero (d < 0.10) or small (0.11 < d < 0.35) range, a few are in the moderate range (0.36 < d < 0.65), and very few are large (d = 0.66–1.00) or very large (d > 1.00). (…) Extensive evidence from meta-analyses of research on gender differences supports the gender similarities hypothesis. A few notable exceptions are some motor behaviors (e.g., throwing distance) and some aspects of sexuality, which show large gender differences. Aggression shows a gender difference that is moderate in magnitude.
As the new millennium got into swing, it looked as if gender was in, sex was out.
But a new article published in Public Library of Science (PLoS) on January 4, 2012, is once more muddying the waters. In “The Distance Between Mars and Venus: Measuring Global Sex Differences in Personality,” psychologist Marco Del Giudice from the University of Turin, Italy, subjected existing data on male/female differences to fresh and more rigorous analysis. He found that “the idea that there are only minor differences between the personality profiles of males and females should be rejected as based on inadequate methodology.” In fact, he discovered, the personality difference between men and women “turns out to be extremely large by any reasonable criterion.”
Specifically, Dr. Del Giudice found that
Most personality traits have substantial effects on mating and parenting-related behaviors such as sexual promiscuity, relationship stability, and divorce. Promiscuity and the desire for multiple sexual partners are predicted by extraversion, openness to experience, neuroticism (especially in women), positive schizotypy, and the ‘‘dark triad’’ traits (i.e., narcissism, psychopathy, and Machiavellianism). Negative predictors of promiscuity and short-term mating include agreeableness, conscientiousness, honesty-humility in the HEXACO model, and autistic-like traits. Relationship instability is associated with extraversion, low agreeableness, and low conscientiousness. Finally, neuroticism, low conscientiousness, and (to a smaller extent) low agreeableness all contribute to increase the likelihood of divorce.
In addition to their direct influences on mating processes, personality traits correlate with many other sexually selected behaviors, such as status-seeking and risk-taking. Thus, in an evolutionary perspective, personality traits are definitely not neutral with respect to sexual selection. Instead, there are grounds to expect robust and wide-ranging sex differences in this area, resulting in strongly sexually differentiated patterns of emotion, thought, and behavior – as if there were ‘‘two human natures’’, as effectively put by Davies and Shackelford.
Dr. Del Giudice’s research essentially shoots down today’s received wisdom that men and women are more similar than they are different without going on to inform us why, say, women can’t read maps and men can’t ask for directions. But I’m intrigued and can sniff a paradigm shift in the wind. What ramifications do his findings have? And what will happen to the emancipatory notion of gender as opposed to the patriarchal menace of sex? Dr. Del Giudice was kind of enough to take time off from his busy schedule to answer some of my questions:
JM: Dr. Del Giudice, for decades now feminists and gender theorists have been arguing that men and women are basically the same deep down and that whatever differences in their dispositions and behaviors we may perceive are due to socio-political conditioning from earliest childhood and lifelong peer pressure. Are you implying with your work that this perspective is outdated?
MDG: In our PLoS paper we argue that sex differences in personality are much bigger than previously acknowledged. However, our data do not speak to the causes of such differences - indeed, some versions of the social learning theory (such as Eagly and Wood's social roles theory) are quite consistent with large differences in behavior.
If you want a general answer, I do believe that many sex differences have been shaped by evolutionary processes, and that men and women do not have the same psychology. This belief is based on a huge body of theory and data, including many studies of other cultures and species. This, however, does not negate that social learning and cultural practices have a place in the development of sex differences. But even our learning machinery is a product of evolution, and males and females seem to have somewhat different versions of it.
JM: As a scientist, what is your view of such pop-psy best sellers as John Gray's Men Are From Mars, Women Are From Venus and Allan & Barbara Pease's Why Men Want Sex and Women Need Love? Do these books have any scientific basis or do they merely exploit popular stereotypes? Many critics suspect the behaviors described there are self-fulfilling, self-perpetuating (and profit-making) prophecies.
MDG: I must admit I never read any of those books. Striking a balance between rigor and popularization is really hard, and I guess many people are asking for simple, black-or-white generalizations. However, I'm not surprised that these books become popular, because men and women are different in many respects, and they (usually) know. People want to learn how to cope with that, and simply telling them that the differences they see do not exist is not going to work. Then, of course, there are a lot of individual differences within each sex, and this is another important aspect of life. There are many ways of being a men or a woman, and this diversity is also a product of both culture and evolution.
JM: Do you have any concern that your findings could play into the hands of religious fundamentalists and other reactionary forces around the world who have a vested interests in keeping the sexes separate, with men on top and women barefoot and pregnant?
No. [We’ll just have to take his word for that!]
JM: If other researchers choose to build upon your findings, what do you see as the possible consequences, both in terms of what we understand about men and women and also public policy?
MDG: On the scientific side, I hope we will build a more accurate map of the psychological similarities differences between the sexes. However, the descriptive approach we adopted in this study would be sterile without good theories of how and why males and females differ. As for public policy, it is a complex issue. I don't think there should be a one-to-one relation between scientific findings and public policy. However, policies that depend on false premises to work will probably fail, or fail to work as intended. Some policies seem to be based on very strict assumptions - e.g., that sex differences in the relevant domain are exactly zero, or that they can be eliminated by social learning. Those assumptions are unlikely to be true. But I'm really not saying anything new here.
JM: On your website you write: "A common thread underlying much of my current work is the application of life history theory and sexual selection theory to the study of individual and sex differences in attachment, mating, social competition, and personality," which sounds utterly fascinating. Can you give us a preview of what we can expect?
MDG: Thanks for the kind words. I work on sex differences in attachment styles and their development, from childhood to adulthood. Some of my theoretical work concerns the evolution of autistic-like traits - a fascinating dimension of individual differences, which also has sex-related aspects. At the moment, I'm doing a lot of interdisciplinary research on the development of the stress response system, including prenatal stress, and some of my future projects will deal with psychopathology. I keep myself busy!
The illustrations for this article are taken from the website 12 Images to Show You the Subtle Difference Between Men and Women.