Gender, Nature, and Nurture - Richard A. Lippa 2014


I dogmatise and am contradicted, and in this conflict of opinions and sentiments I find delight.

—Samuel Johnson

Nature and Nurture came together one day to have tea in an outdoor café. As they sat and observed the people about them, their conversation turned to the nature of women and men. The following is a transcript of their impromptu discussion.

Nature: I'm glad we finally have a chance to sit down for a civilized cup of tea. I don't have to tell you that it gets a little wild where I'm from.

Nurture: I can see by the stains on your clothes. I don't wish to criticize, but you really shouldn't stick your fingers out when you lift your cup.

Nature: Well, I haven't had the benefit of your upbringing.

Nurture: Anybody can learn, with the proper environment.

Nature: It takes some native ability too.

Nurture: Let's not start that again!

Nature: You remember the last big fight we had?

Nurture: What were we discussing that time?

Nature: Intelligence!

Nurture: Well, for heaven's sake, let's stay away from that topic today. Let's chat about something that's not controversial, like all the rest of these people. Let's have a normal conversation for once. Did you overhear those women over there, discussing fashions and recipes? Those are safe topics. I have a great new recipe for a vegetarian "meatloaf" that I can share it with you, if you're interested. And listen to that group of men over there, arguing about football and cars. What do you think? How will the 49ers do this year?

Nature: St just goes to prove what I've said all along. Men and women have different natures.

Nurture: Oh no, not again! I'm sure it comes as no surprise to you to learn that I disagree with you. For an elemental force, I find you to be really behind the times. This is the 21st century! We've moved past the sort of essentialist nonsense you just spouted about the nature of gender!

Nature: I don't think it's nonsense to say that men and women have different natures. I just began to read a book entitled, Gender, Nature, and Nurture

Nurture: Yes, I started to read the very same book. Quite interesting. Made a number of good points about the importance of nurture. But some of the arguments on the other side seemed a bit strained to me.

Nature: Really! My take on the book was just the opposite of yours. There were a number of excellent points about biological influences on men and women's behavior. However, much of the stuff about nurture seemed rather farfetched to me. Wordy too. The author needed a good editor

Nurture: You're right there. The chapter on biology could have been pruned down considerably. It was quite repetitious. And many of its arguments were specious to boot. All that stuff on animal research, about hormones affecting the nervous system, sexual behaviors, and so forth. Let's be realistic. We know that human beings are much more complex than lower animals. We have higher thought processes and culture. We are conscious thinking beings.

Nature: I didn't know you were human.

Nurture: Don't be ridiculous. I am what makes humans human. Without the benefit of nurture, humans would be no better than animals. Let me use sex as an illustration.

Nature: By all means! I like to talk about sex!

Nurture: That doesn't surprise me. But as I was saying, we all know the mating of animals is largely reflexive. But human sexuality is largely learned. When people make love, they have feelings, fantasies, and romance. Human sexuality is molded by cultural influences; it is socially constructed.

Nature: But you are ignoring a fundamental fact: People are animals. We eat and drink, we breathe and bleed. We have all the basic bodily functions. We are DNA-based organisms, and we have evolved just like amebas, lizards, and rats.

Nurture: I didn't know you were human.

Nature: I am everything. I embrace the whole spectrum of living things. That's my point exactly. People are a part of nature. There's no escaping it.

Nurture: But you overstep yourself. You are not everything. That's your problem. You think everything can be reduced to DNA: genes, hormones, and nerve impulses. To you, everything is a Darwinian struggle, "red in tooth and claw." But let me tell you, there's more to human beings than their biological parts. And there's more to men and women than their genes and genitals. There are emergent properties you don't acknowledge, things like consciousness, beliefs, language, and culture. These things are learned, and they cannot be readily explained by biology.

Nature: I'll concede this much: consciousness, language, and culture complicate things. But biology can have a direct influence on human behavior, despite the factors you cite. Cultures across the world vary in their cuisine; however, people all over the world like sweet and fatty foods. Cultures provide variations on a theme, but the basic themes are biologically set.

Nurture: I thought we were talking about gender.

Nature: Okay, let's talk about gender. Let's return to one of my favorite topics—sex. You read that book. The evidence is quite clear. Across the world, despite cultural variations, men are more interested in casual sex than women are, they desire more sexual partners, and they prefer youth and beauty in a mate more than women do. In contrast, women are more interested in a mate's wealth, status, and dominance than men are, and they are more monogamous. These differences must be due to biology.

Nurture: But you are ignoring the fact that men have more power and status the world over.

Nature: Well, why do men have more power and status?


A Darwinian pick-up line. Has evolution led men and women to prefer different traits in a mate?

Nurture: I repeat, men have more power and status the world over. And people who have power and status can pick young, attractive things for dates and mates. On the other hand, if you are economically dependent—as women traditionally have been—then it's important for you to mate with someone who has power, money, and status. But things have changed, now that women are less oppressed and more economically independent...

Nature: Women still prefer good earnings and status in a mate more than men do, according to recent research.

Nurture: Well that will change, as the two sexes come closer to achieving equality.

Nature: You seem to have forgotten David Buss's study of 37 cultures across the world and David Schmitt's fascinating recent cross-cultural studies of men's and women's sexual styles. The sex differences they found in mating preferences and sexual styles were quite consistent across cultures, and this implies that there are biological factors as work. I know you don't want to hear these words, but I'm going to say them anyhow: There are biologically determined sex differences in human sexual behaviors and mate preferences.

Nurture: I'm glad you brought up Buss's research because there was a very interesting article in the American Psychologist by Alice Eagly and Wendy Wood (1999) that challenged Buss's evolutionary position, using Buss's own data.

Nature: You read a lot for an elemental force.

Nurture: Don't be silly! I am synonymous with cultural learning. Of course I keep up with current knowledge!

As I was saying before you interrupted, Alice Eagly and Wendy Wood analyzed David Buss's own data from more than 30 different cultures, and they showed that the size of sex differences in mate preferences depends on women's status in those cultures. Sex differences in preferences for a mate's earning potential were particularly large in societies in which women had low status and education. However, sex differences were smaller in societies In which women had higher status and more education. Clearly, what you claim to be a biologically determined sex difference varies a lot depending on cultural and economic factors.

Nature: But was there any culture in which men valued the earning prospects of a mate more than women did?

Nurture: Well, no...

Nature: There you go! Of course there are cultural variations in mate preferences. No one denies that. But there are still consistent sex differences, despite all the cultural variations. And the only plausible explanation for these consistencies is biology. They are due to nature, in short.

Nurture: You just don't understand what I'm saying!

Nature: I understand you all right; however, I'm looking at the data in a different light. You want to emphasize cultural variations in sex differences. However, I want to emphasize cross-cultural consistencies in sex differences and argue that only biology can explain these consistencies. David Schmitt's (in press) recent work on committed versus uncommitted sexual attitudes found that sex differences were more than twice as large as differences across nations and cultures.

Nurture: I must remind you that cross-cultural consistencies in sex differences can result from sexist institutions and social roles that are common across cultures. Furthermore, I must remind you that Schmitt clearly stated in his paper that there was substantial evidence supporting social role theory in his data.

Nature: That's true. So maybe both biological evolution and social roles play a role in molding men and women's sexuality. But let's look at another example, sexual orientation. You must agree there's a huge sex difference there. Most men are sexually attracted to women and most women are sexually attracted to men. Surely you admit this is largely due to biological factors.

Nurture: Not necessarily. As I was telling you before, human sexuality is socially constructed. In most cultures, people are taught heterosexuality from birth on.

Nature: But you are familiar with the evidence. Variations in prenatal androgen exposure affect masculine and feminine sexual behaviors in rodents and monkeys. Studies of humans exposed to unusual levels of sex hormones also show a link between prenatal hormones and adult sexual orientation. You read that book.... I don't need to say more. The evidence is really overwhelming—don't you think?—that biology plays an important role in sexual orientation.

Nurture: Not necessarily. You talk about human sexual orientation as if it were some immutable, fixed thing. Let me quote from Anne Fausto-Sterling's (1992) excellent book, Myths of Gender, which argued against LeVay and others of his ilk who wish to make sexual orientation a simple, gender-linked trait:

Human behavior... is much more complex than [LeVay] admits. How can he explain the football hero—masculine to the core—who is nevertheless gay? And what about the highly feminine lesbian, the straight man who fantasizes about having sex with a man while making love to his wife or who experiences sexual arousal from anal penetration, the lesbian who fantasizes about penile penetration while making love to her lady friend, or the well-known phenomenon of situational homosexuality that occurs in institutions such as prison? These examples reiterate that human sexuality is not an either/or proposition. Nor do sex roles necessarily mirror sexual orientation. (Fausto-Sterling, 1992, p. 249)

Nature: Whew, that's a real mouthful! Did you memorize all that?

Narture: Yes. I'm a quick learner.

Nature: You must be. But to return to Fausto-Sterling, I think she is mixing apples, oranges, and rutabagas in that passage. Let me try to untangle some of it. First of all, I must say that it seems quite strange for a social constructionist like Fausto-Sterling to describe any man as "masculine to the core." However, for once I find myself in agreement with her, for I do believe that some men are "masculine to the core" and that some women are "feminine to the core." Why? Because it is in their biological natures!

In response to the straight man who fantasizes about having sex with a man while making love to his wife, my answer is simple. Chances are, he's not really a straight man! Similarly, the lesbian who fantasizes about penile penetration while making love to her lady friend is not truly a lesbian; she's either a heterosexual woman experimenting with lesbianism or she's bisexual. And situational homosexuality—as occurs in prisons—is no big deal. The question is, what do these men prefer once they are out of prison? If they resume sexual relations with women, chances are they are straight. If they continue having relations with men, chances are they are gay.

Fausto-Sterling created unnecessary conceptual confusion when she failed to distinguish between sexual behaviors, which of course are molded by social forces and environmental opportunities, and sexual desires. When I speak of human sexual orientation I am speaking, most fundamentally, of one's sexual desire for men or for women. This is the aspect of sexual orientation that I believe is most influenced by biology.

Nurture: Now I am going to trap you with your own words!

Nature: Uh oh!

Nurture: You just defined sexual orientation in a totally different way from most of the animal studies you admire so much. In these studies, sexual orientation is defined in terms of mounting behaviors and sexual presenting. Do these behaviors assess desire for males or desire for females? I think not.

Nature: Well, you must admit it's hard to assess a rat's desires

Nurture: Then admit that you are measuring quite different things in animal and human studies. And if you admit this, then you must admit also that studies on the effects of sex hormones on animals' so-called masculine and feminine sexual behaviors don't tell us very much about human sexual orientation.

Nature: Are you through?

Nurture: For now.

Nature: Then I want to make one final comment about Fausto-Sterling. I believe she was simply wrong when she claimed there is no relation between sexual orientation and other aspects of gender. Recent research shows there are strong links between sexual orientation and some measures of masculinity and femininity. Furthermore, children who are gender nonconformists—feminine boys and masculine girls—are much more likely than gender-conforming children to grow up to be homosexual adults. All of this evidence points to the strong likelihood that there are biological factors that influence both sex-typed behaviors and sexual orientation.

Nurture: Not so fast! You forget that there are gay and lesbian subcultures that influence the adoption of supposedly masculine and feminine behaviors, just as mainstream society socializes the masculine and feminine behaviors of the majority.

Nature: I just don't understand your resistance on this topic. It seems so obvious to me that biology influences sexuality. If biological evolution molded any aspect of gender, wouldn't it be sexual behavior and, in particular, sexual orientation? If sex is about anything, it's about sex; that is, if male and female have any biological purpose whatsoever, it is reproduction and genetic recombination. Darwinian evolution is all about reproduction. I think you are being simply wrongheaded when you refuse to acknowledge that biological evolution molded sexual orientation and other aspects of human sexuality. But I don't want to beat a dead horse. Let's move on.

Nurture: That sounds like a good metaphor for your theorizing, although it seems you're beating dead rats more than horses. But neither provides a particularly good model for human sexuality.

Nature: Let me ask you a more general question about gender. And be honest now. Are you really claiming that there are no biological differences between men and women?

Nurture: No, obviously not. After all, men have penises and women have vaginas.

Nature: And that's it? Sometimes you make me want to scream!

Nurture: Well, why don't you go howl with some hyenas? It seems to me that you have more in common with them than with human beings. Look, I'll concede a point, just to calm you down. I do believe there are some biological differences between women and men, beyond the fact that men have penises and women have vaginas.

Nature: Okay, that's better... I feel a little calmer now. What are the other differences you think are due to biology?

Nurture: First of all, men are bigger than women and have greater upper body strength. Second, women carry babies, and they lactate and nurse.

Nature: And that's it?

Nurture: Don't be silly. That's enough. Do you realize how important these differences have been over the history of the human race? In prehistoric times, men were more responsible for hunting and warfare because of their greater size and strength and because they were not tied down by pregnancy and lactation. On the other hand, women were more responsible for child care and close-to-home foraging because they were tied down by pregnancy and nursing.

Nature: Ah, I think I'm going to trap you with your words now.

Nurture: Uh oh!

Nature: Look, you said that men are bigger than women and that men have greater upper body strength than women. But why is this so? Evolutionary theory is the only reasonable explanation for these differences. The reason men are bigger and stronger is because of sexual selection. Ancestral men must have competed with one another for status and mates. I can give you some papers to read....

Nurture: Don't bother. I read more than you think. So what if men are bigger than women? Look, I'm not a member of the Flat World Society. I believe in biological evolution. I do not believe, however, that evolution directly explains sex differences in human behavior. You promulgate an altogether too deterministic and reductionistic form of evolutionary theory for my taste. I repeat, the only evolved sex differences that I'm willing to concede to you are that men evolved to be larger and to have greater upper body strength and that women evolved to give birth and lactate. All the rest is learned and cultural. I don't have to restate it. Reread that book we were discussing earlier—particularly the chapter entitled, "The Case for Nurture."

Nature: You are so infuriating!

Nurture: Go howl with your hyenas!

Nature: No, I refuse to be goaded. And I'm not going to let go of what I just said. The best explanation for why men are larger than women is sexual selection. And if human males did indeed evolve to be physically larger than women because of sexual selection, then they likely also evolved behavioral traits, such as male-on-male aggression, dominance, and status-seeking. These are the traits that helped ancestral males get mates in the past.

Nurture: Oh, all this ranting and raving about ancestral males! It gets so tiresome. Were you there, during this mythical ancestral past? No, of course not. You and your evolutionary friends incessantly make up these "just so stories,"* which explain everything under the sun, after the fact. But you fail to see the obvious environmental explanations right under your noses.

Nature: You folks do pretty well with "just so stories" yourself. For years you've been preaching that gender differences and gender variations are a matter of parental treatment. Then psychologists looked carefully into this claim, and low and behold, they found that parents treat boys and girls more alike than different. Furthermore, they concluded that when parents do treat boys and girls differently, it may be in response to the children's behavior rather than because of any desire to enforce gender stereotypes.

Then you and your friends come up with a new dogma, that sex differences are caused by the mass media. But this makes no sense because influences like parental rearing and the mass media should make same-sex siblings more similar to one another in their masculinity and femininity. However, behavior genetic studies show that same-sex siblings in a given family are no more similar than strangers are, once you account for genetic influences. You people make up "just so stories" too, when they suit your purposes. It's just that your "just so stories" are always environmental ones.

Nurture: Look, you clearly didn't read that book very carefully. No one denies that gender socialization is a very complex process. It depends on parents, teachers, and the mass media. Children's peers are also very important. And to make matters even more complex—and this supports what I said earlier—people are conscious, thinking beings. People have self-concepts. They learn gender stereotypes. And then there's also the whole matter of sexist institutions. Let's face up to the complexity. We don't need to accept your simplistic alternative, that all observed sex differences are due to biology.

Nature: You simply didn't understand the compelling evidence for biology presented in that book.

Nurture: I understood it! I also understood all the flaws in that evidence. First of all, there's the problem of over-generalizing from animals to human beings. Then there are all those claims about testosterone levels being linked to people's aggressiveness, criminality, personality, and visual-spatial abilities. Well, any introductory psychology student could criticize those findings. They're all correlational! We don't know what causes what. You would like to conclude that testosterone causes aggression and dominance and so on. But correlational studies don't allow such cause-effect inferences. Aggressiveness may elevate testosterone levels, rather than testosterone causing aggressiveness.

Nature: But there's a lot of convergent evidence by now, from an awful lot of studies on testosterone...

Nurture: I am not finished! And then, all that research about people with atypical hormones and genes is hopelessly flawed too. You folks claim that CAH girls are masculinized because of high prenatal androgen levels. But these girls often appear different at birth. Their genitals are often masculinized and then surgically "corrected." The parents of CAH girls know about their daughters' condition. Sometimes these girls are even mistaken for boys at birth. It's clear to me that there are lots of ways in which parents may treat CAH girls differently from non-CAH girls.

Nature: But some studies have taken genital masculinization into account, and this doesn't seem to affect their findings. And research on girls exposed to DES does not suffer from the confounding problem of genital masculinization.

Nurture: The results of that research are much weaker.

Nature: But...

Nurture: Don't interrupt me! I'm not finished! Then you and your friends go on and on about people with androgen insensitivity. When testosterone doesn't organize the nervous system, you claim, people develop as females. But you ignore the obvious fact that androgen-insensitive individuals look like females, and therefore they are reared and treated as females. So it's obvious to me, the reason androgen-insensitive people are feminine is because of socialization.

Nature: What about reductase-deficient boys, who grow penises at puberty?

Nurture: Some of them look genitally ambiguous, and they may be reared differently from normal girls.

Nature: What about Reiner and Gearhart's work on cloacal exstrophy boys born without penises?

Nurture: Too preliminary. Hasn't been replicated by independent researchers yet. Some have already reported contradictory results (Schober et al., 2002). Let's wait and see if it's for real.

Nature: What about the "John/Joan" case? For years you and your friends have claimed that this case proved that gender identity is learned and a product of socialization. You argued that a genetic boy could become a girl if he were reared as a girl from an early enough age. Now it turns out that "Joan" was never really comfortable as a female, and he reverted back to being a male. Biology won out! Admit it!

Nurture: It's only a single case study, and therefore not definitive. Furthermore, "John" was castrated at a relatively late age and his parents were probably conflicted over the whole matter. It doesn't necessarily prove anything.

Nature: But there are other similar cases reported in the literature.

Nurture: And I remind you that in at least one of these cases, an XY individual was castrated, reared as a girl, and she accepted a female gender identity (Bradley, Oliver, Chernick, & Zucker, 1998).

Nature: But I remind you that even with her female gender identity, this individual is sexually attracted to women and works in a masculine job—as a mechanic, or something like that.

Nurture: Notice how you focus only on the facts that support your case.

Nature: You should talk! You pick and choose only studies that are consistent with your point of view!

Nurture: You should talk! You ignore half a century's worth of research on gender socialization from psychology, sociology and anthropology.

Nature: That's not true! I simply see flaws in that research.

Nurture: Like what?

Nature: We both read the same book, so we can agree on some things. Remember those studies on similarities between parents and children? Working mothers produce children who are less sex-typed. Siblings influence their brothers' and sisters' sex-typed behaviors. I don't have to repeat all those findings. I'm sure you're familiar with them.

Nurture: Yes, it's clear that parents and siblings have a big effect on children's masculinity and femininity.

Nature: But what's the nature of the effect? This research is all correlational; we don't know what's causing what. None of these studies ever mentions the possibility that parents and children are similar because of shared genes. We cannot understand the impact of parental rearing without acknowledging the possibility of genetic influences. There is a fundamental flaw in most existing research on gender socialization, and that flaw is that the research never even considers the possibility that parents and their children share genes. This fundamental flaw renders much socialization research unin-terpretable. Admit it!

Nurture: I will not.

Nature: Furthermore, behavior genetic research shows that common family influences on people's sex-typed behaviors are very weak. Gender socialization, which you seem to think is so overwhelmingly important, just doesn't have the powerful effects it should have on all the boys and on all the girls in a family. The evidence is clear that boys and girls bring strong predispositions—genetic predispositions—to gender socialization. One might even say that they bring different natures to gender socialization.

Nurture: You really need to read that book again and review the evidence about how parents encourage different kinds of play in boys and girls ...

Nature: I'm glad you brought up the topic of play. First of all, I insist that you acknowledge that parents may be responding to girls' and boys' different toy preferences rather than creating them. The evidence is clear. As early as researchers can observe children, boys and girls show different toy preferences and play styles. There must be something innate going on here. Did you know that even monkeys show sex differences in their toy preferences and play styles? Male monkeys engage in more aggressive, rough-and-tumble play and prefer mechanical toys; female monkeys play more with doll-like toys (Alexander & Hines, 2002; Meaney, Stewart, & Beatty, 1985).

Nurture: Look, I'm not willing to concede anything to you about sex-typed toy play in human beings. Forget about monkeys. Human gender socialization and cognitive learning starts at birth (Martin, Ruble, & Szkrybalo, 2002). Even if there are sex differences in children's toy preferences by the second year of life, these children have already had more than a year to learn those differences, a year of parents handing them different toys and encouraging different play activities, and a year of learning about differences between males and females.

Nature: That's an implausible explanation for such an early, pervasive, and cross-species sex difference.

Nurture: Is it more plausible that there are doll centers in girls' brains and truck centers in boys' brains?

Nature: That's putting it in a derisive way. But yes, there are innate predispositions, which ultimately must have some physiological basis, that lead the boys and girls to prefer certain kinds of activities to others. And what about sex differences in occupational preferences? Men more prefer realistic occupations; they like being mechanics, farmers, and plumbers. Women more prefer social and artistic occupations; they like being social workers, teachers, nurses, and editors.

Nurture: But a lot of men prefer those occupations too!

Nature: But on average, men more prefer thing-oriented occupations, and women more prefer people-oriented occupations. This difference is quite large. And I'm sure you recall that recent behavior genetic research indicates that over 50% of individual differences on the people-things dimension are due to genetic influences. Surely, you can't believe that the huge observed difference between men and women on the people-things dimension is due entirely to environmental factors?

Nurture: I do indeed. The fact that individual differences are highly heritable within each sex does not necessarily tell us anything about the causes of gender differences. I believe that gender socialization is the reason why women and men prefer different kinds of occupations.

Let me remind you of Jacquelynne Eccles' research, which found that parents have different expectations for their daughters' and sons' math performance and furthermore that these expectations influence girls' and boys' estimates of their own abilities. Eccles' research helps explain why men are more likely than women to choose thing-oriented fields like engineering and natural sciences.

In addition, there are also other powerful situational pressures, as you very well know. For example, it is obvious that university science and engineering departments create notoriously hostile environments for women to work and learn in. It's no wonder that women avoid these settings and their related occupations. And I remind you that powerful social roles have continually channeled women into low-status occupations throughout history. Until gender stereotypes are abandoned and gender roles dismantled, we cannot say with any certainty what the true occupational preferences of women and men are.

Nature: I'm glad you brought up Jacquelynne Eccles' research. You must be aware that a number of studies have used Eccles' data to investigate the power of self-fulfilling prophecies (Jussim & Eccles, 1995; Jussim, Eccles, & Madon, 1996; Madon et al, 1998). In general, these studies have shown that teachers have pretty realistic assessments of their students' abilities and that self-fulfilling prophecy effects are pretty weak. I think you over-estimate the power of gender stereotypes to guide people's occupational choices, and you under-estimate people's innate preferences.

Nurture: Preferences need not be innate. The studies on self-fulfilling prophecies that you mention in no way invalidate Eccles' findings that parents have different expectations for sons and daughters and that these expectations affect sons' and daughters' beliefs about their own competencies.

Nature: But consider this: Women's occupational pursuits have changed enormously over the past several decades, at least in industrialized countries. The Women's Movement has had a major impact. Women have gained more and more access to higher education. As a matter of fact, a majority of all college students in the United States are now women. Women have entered high-status occupations in ever increasing numbers. Nonetheless, there remain large sex differences on the people-things dimension. Most women just don't seem drawn to fields like engineering and physics (Browne, 2002).

Nurture: You're wrong. It varies from country to country. In Hungary, half the university physics teachers are women (Dresselhaus, Franz, & Clark, 1994). And I remind you, gender differences in occupational choices are still confounded with status differences between the sexes.

Nature: But women are drawn to some high-status occupations, like medicine, law, and the social and biological sciences. I believe this is because these fields are more on the "people" side of the people-things dimension. Don't you think that some of the sex differences on the people-things dimension may be due to biological factors?

Nurture: I do not.

Nature: How about all the research on sex differences in visual-spatial ability? These differences are consistently found and they are quite large, at least for certain kinds of spatial ability. Men score a lot better on mental rotation tests than woman, for example.

Nurture: But women do better on spatial location tests than men.

Nature: That's true.

Nurture: I still don't believe any of these differences are due to biology. Girls and boys have very different learning experiences throughout childhood. They play with different kinds of toys. They participate in different kinds of sports. They take different math and science classes.

Nature: Could some of these childhood differences result from differences in visual-spatial abilities rather than causing them? Recall that sex differences in visual-spatial ability are quite consistent across cultures. Recent work suggests that these differences are present in young children, and there is intriguing recent evidence that nonhuman primates also show sex differences in spatial abilities (Kimura, 1999). Surely biology must play a role in all of this.

Nurture: I don't think so.

Nature: Well, just as a thought experiment, I'd like you to suspend your disbelief for just a second. Imagine that there were a biologically based sex difference in certain kinds of visual-spatial abilities. Do you think that this could lead men and women—on average—to prefer different kinds of occupations?

Nurture: I reject the premise of your question.

Nature: But it's just a thought experiment.

Nurture: You know, for years people have claimed that so-called men's work and women's work were dictated by native abilities and innate preferences. And usually, women were portrayed as have some kind of deficit in comparison with men. But this is just hogwash. Jobs do not have genitals!

I refer you to a compelling article by Janet Shibley Hyde (1990) that offers some calculations to refute just the kind of argument you are making. She assumed—for the sake of discussion—that to be an engineer, a person requires spatial abilities in the top 5% of the population. Assuming a d-value of 0.40 for sex differences in overall spatial ability, 7.35% of men and 3.22% of women would have the requisite level of spatial ability to be an engineer. This suggests the ratio of male to female engineers should be around 2-to-1. But in fact, the ratio is more like 20-to-1. This means that there must be other factors—social factors—which lead to such huge differences in the number of men and women who pursue careers in engineering.

Nature: But those other factors could just as well be other innate abilities and traits. Hyde's assumptions are mere conjecture, as I'm sure you'll agree. But let me play her game, just the same. First, I'd like to point out that some sex differences in spatial ability are larger than her assumed d-value of 0.4. More importantly, there are sex differences in other abilities that are also very important for success in engineering, such as math ability and mechanical aptitude, and the differences are largest at the highest levels of ability Furthermore, men on average are more thing-oriented than women are, and this difference is large. If we combine the effects of all of these sex differences—in visual-spatial ability, math ability, mechanical aptitude, and people-versus-thing-orientation—it becomes more understandable why the male-to-female ratio in engineering is 20 to 1.

Nurture: You are adjusting your assumptions to fit your conclusion.

Nature: Just as Hyde was. However, at least Hyde acknowledged that professions like engineering do in fact require exceptional skill and abilities in certain domains. To be an outstanding engineer or physicist, for example, it is not sufficient simply to be above average in math ability. You must be outstanding in math. You know, I think you're setting yourself up for a big fall.

Nurture: What are you talking about now?

Nature: You're always criticizing biological theories, and you're always stating that the biological research is primitive and flawed...

Nurture: I'm glad you used those words. You are so right! The brain sciences are still in their infancy. Our understanding of the biology of human behavior is quite primitive. There is much we do not understand, including the neural bases of memory, learning, thought, emotion, and sexuality. Even if there were some bona fide gender differences in brain structure—and the current evidence on this topic is highly debatable, in my opinion—who knows what these differences mean?

Neuroscientist Marc Breedlove (1994) put it well. All psychological phenomena—including learning, memory, and motor skills—must be a function of the brain. However, to say that behavior is a function of the brain is not to say that behavior is innate. The human brain is extraordinarily plastic. Gender differences in brain structure may result from gender differences in learning, experience, and socialization.

Nature: But more and more research is honing in on gender-linked biological processes—particularly prenatal androgen levels—and the evidence is growing stronger and stronger that these processes influence later behaviors. I don't need to repeat it all... you read that book!

Nurture: The recent findings about the influences of prenatal hormones on humans and on physical markers of hormones and behavior are very preliminary. The findings haven't settled down yet, and I'm not ready to accept that these studies have convincingly demonstrated biological causes of gender-related behaviors.

Nature: Well, this brings me back to my earlier comment that you're setting yourself up for a fall.

Nurture: What exactly did you mean by that?

Nature: It's clear to me that biological knowledge is increasing at an exponential rate. The Human Genome Project will soon generate huge advances in knowledge about the biological causes of human behavior. I foresee major discoveries about the biology of sex and gender in the near future. People with their heads in the sand—like yourself, I'm afraid—are going to be surprised by many of these soon-to-come findings. By summarily rejecting all biological influences on gender, you are setting yourself up to be refuted.

Nurture: Look, the biological determinists have been declaring victory for more than a century now, but their evidence remains muddy and unconvincing. I suspect it will remain so for a very long time to come. And you ignore the fact that psychologists, sociologists, and anthropologists continue to study gender too. Undoubtedly, there will be major advances in their research as well.

Nature: I'll make this prediction to you. Social science in the 21st century will need to be biologically informed, or it will be doomed to failure. Now note, I'm not saying that biology will supplant the social sciences, but I am saying that social sciences need to form a strong partnership with biology. I recommend Edward O. Wilson's (1998) fascinating book, Consilience, in which he argued for the unity of ail sciences.

Nurture: Isn't that the same Edward O. Wilson who is the father of modern sociobiology? I'm not likely to accept his philosophy of science. He's always been guilty of over-generalizing from animals to human beings, and he's always making grandiose claims about the power of evolutionary theory to explain human social behavior. I think Wilson should stick to his original love—studying ants—and leave the study of people to others!

Nature: As I said before, you may choose to stick your head in the sand.

Nurture: But perhaps you are the ostrich here! I haven't heard you discuss any social psychological research on gender. Anyone who's serious about the topic of gender knows that social forces create, enforce, and sustain the behavior of women and men. Read that book again. People act in ways that are consistent with their gender stereotypes.

Nature: But a lot of recent research shows that gender stereotypes are often quite accurate (Eagly & Diekman, 1997; Hall & Carter, 1999). People are not making up what they believe about men and women. Social reality creates gender stereotypes more than gender stereotypes create social reality.

Nurture: Alice Eagly's social role theory acknowledge that apparent social reality creates gender stereotypes. But let's extend your analysis a step further. Gender stereotypes sometimes reflect social reality, but social reality is often created by the powerful and invisible hand of social roles. Change gender roles and you will change women's and men's behavior. And ultimately, you will change the gender stereotypes that result.

Nature: You go on and on about self-fulfilling prophecies and behavioral confirmation. But all of the social psychology experiments you cite are really only plausibility demonstrations. All they show is that, under very controlled and ideal experimental circumstances, social psychologists can demonstrate statistically significant behavioral confirmation effects. But these are not necessarily large effects. I told you before that recent research shows self-fulfilling prophecy effects are often quite weak in real-life settings.

The same criticism applies to stereotype threat experiments on women's math performance, which are often conducted on high-ability women from elite universities. However, we don't know how much these effects occur in real-life settings. Furthermore, if you look closely at stereotype threat experiments—and I'm sure you have—you'll notice that they often don't study subjects' raw test scores. Rather, they statistically "correct" test scores based on subjects' previous SAT performance. In addition, some of these experiments compute test scores in strange ways, for example, as the proportion of questions a person gets right out of just those questions attempted. This is not how real SAT or GRE tests are scored, if you want to claim that stereotype threat effects are large and significant in the real world, you'd better conduct studies that use real-life tests and testing procedures on representative populations of women and men. Indeed, recent analyses of real-life data don't find evidence for stereotype threat effects (Cullen, Hardison, & Sackett, 2004; Sackett, Hardison, & Cullen, 2004). Deep down, I think the stereotype threat effect has been oversold.

Nurture: You make me so mad! You want to dismiss every careful piece of research that demonstrates the social origins of gender differences.

Nature: No, I simply want you to be as critical of social psychological research as you are of biologically oriented research. Furthermore, even assuming that there are stereotype threat effects, what do you suggest as a remedy? Should women have extra points added to their SAT math scores? That hardly seems fair. Not to mention that it would bolster negative attributions about women's math abilities. Should universities stop requiring SAT math scores, even though these scores are quite useful for selecting engineering and natural science students? That's really throwing the baby out with the bath water! Do you want women to take tests only in all-women groups? What attributions will women make about their abilities if they require special test-taking settings, and furthermore, what happens later when women must solve math problems in real-life mixed-sex settings?

Nurture: You're really getting way off track here! The central point I was trying to make is that gender stereotypes have the power to undermine women's performance in some settings. The key point is that we don't need to propose innate sex differences to explain sex differences in test performance.

Nature: You know, this discussion triggers a much broader complaint I have about psychological approaches to gender. According to many psychologists, everything's a matter of thought processes. Psychologists make it seem as if people think their way into gender.

Nurture: But they do, in an important sense. I keep telling you, thought processes are important in human beings. Gender is a matter of beliefs, stereotypes, and expectations.

Nature: But you are ignoring an important finding in the developmental literature. Children display sex-typed behaviors before they achieve the ability to label their own or others' gender correctly.

Nurture: Primitive gender cognitions occur very early, before the verbal labeling of gender emerges (Martin, Ruble, & Szkrybalo, 2002). Furthermore, no one ever argued that gender labeling is the only route to sex-typed behavior. Conditioning, reinforcement, and modeling are important too, particularly when children are very young. And I must remind you that when children are able to accurately label gender, their behaviors are affected. For example, gender labeling can affect sex segregation and aggression in girls.

Nature: Sometimes. But again, sex-typed toy preferences and play precede gender labeling (Serbin et al., 2001).

Nurture: Look, it's clear that thought processes are important in the development of gender. You can't tell me that boys are born feeling that doll play is repellent, embarrassing, and disgusting. Even if boys are born with a preference for certain kinds of play—which I don't believe—this cannot explain why boys derogate girls' toys and play.

Nature: Well, there certainly are some interesting psychological processes going on there, which could be related to the development of in-group and out-group feelings.

Nurture: And these are cognitive processes, which social psychologists have studied intensively.

Nature: I still think you and your psychologist friends have grossly overestimated the impact of cognition on gender-related behaviors. In my view, gender cognitions are often epiphenomena; they float above gender-related behaviors. They come after the fact. I remind you once again that the relationship between children's gender beliefs and their sex-typed behaviors is often quite weak.

Nurture: But I remind you that experiments on adults show a clear link between gender stereotypes and behavior. Consider all the studies on self-fulfilling prophecies, behavioral confirmation, and stereotype threat.

Nature: But as I told you before, these experiments are plausibility demonstrations rather than demonstrations of real-life effects. Let's use the "Baby X" studies as an example. For the purpose of experimental control, researchers briefly present the same baby—sometimes labeled as a male and sometimes as a female—to adults who are asked to judge or interact with the baby. In other words, the researchers present the adults with standard stimulus materials, so that any differences in their reaction to the baby "boy" or "girl" can be attributed to gender labeling and gender stereotypes. But in real life, you are not faced with standardized he's and she's. Rather, you are faced with actual boys and girls, who do in fact behave in different ways, have different preferences, and respond to your actions in different ways (Lewis, Scully, & Condor, 1992).

Consider also studies on the effects of gender stereotypes on judgments of adult men and women. Experimenters present us with impoverished stimulus materials—a photograph of a person or a person described by a few trait words or by a transcript—and then ask us to judge this person who has been labeled as either as "John" or "Joan." But in real life we do not judge such phantom people. Rather, we judge people who behave, talk, and interact with us, who provide us with a huge amount of rich, individuating information Research shows that when we judge people based on lots of information, the information wins out and stereotypes have only weak effects (Kunda & Thagard, 1996).

Nurture: Even if the effects of stereotypes on people's judgments are weak—which, by the way, I don't buy—stereotypes exert their effects over and over again, and these cumulative effects may be much stronger than any single effect. If teachers hold even weak beliefs that boys are more able than girls in math, then imagine the cumulative effect of these beliefs, when teachers interact hour by hour, day after day, and year after year with girls and boys. It's not as easy to assess the real-life effects of stereotypes as you suggest.

Nature: I don't think we're going to make any headway here,

Nurture: Not if you remain as pigheaded as you've been.

Nature: Okay, let's change topics, then. We've already discussed sexuality. But what about aggression? Surely you must believe that biology contributes to sex differences in physical aggressiveness.

Nurture: Not necessarily.

Nature: But the evidence is so consistent and varied. Sex differences in aggression occur at an early age, and, if anything, they are stronger in children than in adults. Our closest primate relatives show sex differences in aggression. Testosterone levels are related to aggression in both animals and humans. Cross-culturally, men are more aggressive than women are, and these differences are particularly large when you focus on extreme forms of aggression such as homicide, violent assault, and warfare.

Nurture: Much of this can be explained by greater male size and upper-body strength. It can also be explained by sexist institutions, patriarchy, social roles, and gender socialization, particularly the socialization of masculinity. We don't need to postulate that men have a higher innate level of aggressiveness than women do.

Nature: But body size cannot explain greater male aggressiveness in young children.

Nurture: Learning and socialization can explain sex differences in young children's aggression. Furthermore, I think you overemphasize the cross-cultural consistencies. There are some cultures—think of the Amish, for example—in which both sexes show very low levels of aggression.

Nature: I don't doubt that both men and women In some cultures display low levels of aggression, often in response to very strong social pressures and ideologies. Absolute levels of aggression undoubtedly vary a lot across cultures, but this doesn't negate the fact that sex differences are also very consistent across cultures. I wish someone would do a careful study of aggression in Amish communities. I'm willing to bet that the rates are higher in men than women, even among the Amish.

Nurture: I'll take you up on that. Let's place a bet on it!

Nature: I accept! If you win, I'll treat the next time we meet for tea.

Nurture: Okay. However, I don't think I can endure another tea with you.

Nature: But we must keep meeting until this is resolved!

Nurture: I doubt if this will ever be resolved. To return to what I was saying, I still don't accept that males are innately more aggressive than females. The socialization of boys to be tough and aggressive is so pervasive that it's premature to accept any biological explanations.

Nature: I'm afraid that there's no empirical evidence that will serve to convince you that any human sex difference is influenced by biological factors.

Nurture: And deep down, I'm afraid there's no evidence that will convince you that human gender differences are the result of learning, socialization, and environmental forces.

Nature: What do you make of the fact that some sex differences—and again, aggression is a good example—are so strong and pervasive?

Nurture: Notice how much, you always focus on differences. You never acknowledge that there is enormous variation within each sex. All the behaviors you focus on—aggression, visual-spatial performance, occupational choices, sexual orientation—show enormous variability within each sex. Your constant harping on differences obscures this fundamental fact!

Nature: This is not my intent at all! Remember, there are two sides to gender: differences between the sexes and individual differences in masculinity and femininity. Masculinity and femininity are all about within-sex variations. And I remind you that behavior genetic research suggests that much of this variation is due to genetic factors.

You may wish to take refuge in the fact that there is a lot of variability among men and among women. But I think this is a false refuge, for these variations, which you take as evidence of the non-reality of gender, are sometimes themselves due to gender-related traits!

Nurture: I view within-sex variability as evidence against simplistic, bipolar, either-or constructions of gender. Society wants to divide humanity into two essential categories: male and female. But reality is not nearly so simple. I refer you to Anne Fausto-Sterling's book, Sexing the Body (2000). Did you know that even in genetic and anatomical terms, a significant number of people are intersex, that is, neither purely male or purely female. Such individuals include CAH females, androgen-insensitive males, Turner syndrome females, reductase-deficient males, true hermaphrodites (people with both male and female reproductive organs or genitals), and others as well.

Nature: Well surely, such individuals must be a small minority.

Nurture: Fausto-Sterling estimated that 1.7% of the population is intersex. This is not a trivial number. In the United States alone, this represents millions of people.

Nature: Some researchers say the proper estimate is a hundred-fold less (Sax, 2002). But you are getting off track. Let's return to the topic of variations among men and variations among women.

Nurture: Intersex people represent one kind of gender variation. I can see why you're uncomfortable. My discussion of intersex individuals questions the very categories of male and female, which are so important to you.

Nature: You are wrong. I am not uncomfortable. Nonetheless, I do think that the biological categories of male and female make sense. They are not merely social constructions. The fact that there are genetic, physical, and developmental anomalies that affect a small percentage of people does not alter the validity of this fundamental biological classification. But again, I would like to return to the topic of variations within each sex.

Nurture: By all means.

Nature: You would like to argue that variations within each sex somehow negate the essential categories of male and female. But I think that this argument is false. Even if there are variations in sexual orientation within each sex, for example, this should not blind us to the fact that there are still huge differences between the sexes. And despite within-sex variations, there are still large sex differences in physical aggressiveness, visual-spatial ability, and people-versus thing-orientation.

In a strange way, variations within each sex offer us a backdoor way of examining the nature and nurture of gender. The very fact that some men are gay, for example, or interested in interior design, or terrible at doing mental rotations shows that monolithic gender socialization—which you claim to be so overwhelmingly powerful—does not take in some people. I suspect that genetic and biological factors provide the explanation for why the behavior of significant numbers of men and women goes against the tide of gender socialization.

Nurture: You are sounding like James Dabbs (2000, p. 211) now: "If [boys] are not masculine, it is more likely because of physiology than parenting." Give me a break!

Nature: But it's true. And there's yet another way that within-sex variations offer us a backdoor entry into probing the nature and nurture of gender. As I've noted before, the socialization factors most emphasized by psychologists and sociologists—parental treatment, social models, and mass media effects—should show themselves as common environmental effects in behavior genetic studies of masculinity and femininity. That is, these nurture factors should equally affect all the boys and all the girls in a given family. They should therefore make all the boys in a given family more similar to one another in masculinity and all the girls' more similar to one another in femininity. But behavior genetic studies show that this is not true!

Something is fundamentally wrong with the classic socialization accounts of gender. Gender socialization does not inevitability and inexorably lead to sex differences and within-sex homogeneity. Rather, it interacts with the biology and temperament of individual boys and girls. Therefore, behavior genetic studies, which are often portrayed to be about genetics, actually tell us something very important about the socialization of gender.

Nurture: I think you place altogether too much faith in behavior genetic studies. Their analyses are based on debatable statistical assumptions about how genes and environments work. Personally, I believe in much more interactive and epigenetic models of development.

Nature: What do you mean by that?

Nurture: At all levels of human development—the genetic, the cytoplasmic, the hormonal, the embryoiogical, the individual, the family, the social, and the cultural—there are complex feedback loops, whereby events at one level influence events at other levels. In such complex systems it's not possible to distinguish between nature and nurture. There are no simple, linear, cause-effect sequences. Genes direct the production of proteins and hormones, but environmental events—for example, being stressed—in return influence hormones, which then serve to turn on some genes and turn off others. The causal arrows go in all directions, across all levels. Environmental factors—nutrition, infectious diseases, maternal stress levels—influence embryoiogical development, and embryoiogical development in turn influences environmental factors—the maternal immune system, for example. Individuals seek out certain environments, which can then influence the action of genes and hormones. No level and no factor is walled off from another, and no factor is causally preeminent.

Nature: Well, at least biological factors have a place in your epigenetic system.

Nurture: Of course they do! I never have denied that we are embodied creatures. What I deny is the primary and preeminent role you assign to biological factors. In your system of thought, biology is always the cause, and behavior is the consequence. I'm afraid the truth is not nearly as simple as that.

Nature: I've heard a number of writers offer the following analogy that asking whether behavior is more influenced by nature or nurture is like asking whether the area of a rectangle is more influenced by its width or height.

Nurture: The point is that they're both important, right?

Nature: Right. However, this analogy goes only so far, I think.

Nurture: Damn! I thought that we would finally be able to end our conversation on a note of agreement.

Nature: End our conversation? But there's still a potful of tea left! Don't you want to hear the limits of the rectangle analogy?

Nurture: I doubt I have a choice.

Nature: I find it scientifically unsatisfying to say, "Both things count," and to leave it at that. If the science of gender is to advance, we must understand how nature and nurture have their effects, and more subtly how they interact.

Nurture: Well, I hate to sound churlish, but I have always felt that you've been exceedingly vague in specifying the precise mechanisms by which biology has its effects on gender. I hear all this talk about hormones, but no one has spelled out—to my satisfaction, at least—exactly how hormones affect aggression, spatial ability, or whatever. You folks talk about sex differences in the hypothalamus, in the corpus callosum. and so on, but no one has come even close to proposing the neural circuitry of sexuality, or of cognitive abilities, or of anything, for that matter.

Nature: Sadly, I must agree with you here. Biological theories have been weak in specifying the mechanisms by which genes, hormones, and brain structures affect gender-related behaviors. I'd like to believe that this deficiency results from the relative immaturity of biological psychology. I expect much progress will soon be made.

Nurture: We'll see.

Nature: But I'd like to return to my dissatisfaction with the rectangle analogy. Let me use some examples. No one doubts that having five fingers on each hand requires both nature (human genes) and nurture (decent nutrition, shelter, oxygen to breathe). But in most normal environments, children will end up with five fingers on each hand, and thus it is a legitimate shorthand to say that the number of fingers on the human hand is an evolved trait and that, at the individual level, this trait is genetically determined. Similarly, no one doubts that learning a human language requires both nature (a functioning human brain) and nurture (a functioning social environment). But most children who grow up in a reasonably normal social environment will learn a native language, and it is a legitimate shorthand to say that the human ability to learn language is innate, but the particular language children learn to speak is socially determined.

The same point can be made about individual differences. It takes both nature (human genes) and nurture (good nutrition and shelter) to achieve adult height. But still, behavior genetic research informs us that, for people reared in reasonably normal environments, most of the variation in people's height is genetically determined. Conversely, although most people who grow up in the United States learn to speak fluent English, it's fair to assume that most of the variations in their accents are socially and environmentally determined.

So yes, it is true that both nature and nurture play an essential role in all human behavior, including gender-related behavior. But it is still legitimate to probe into the relative contributions of nature and nurture to specific kinds of traits and behaviors among people who inhabit reasonably normal social and physical environments.

Nurture: But I must constantly remind you that current so-called normal social environments are sexist environments. We may not be able to learn some key facts about the nature and nurture of gender until women achieve full equality in our society, that is, until currently normal environments become abnormal!

Nature: At last we have found a point on which we can agree! A fascinating social experiment is now in progress. Economic transformations and the modern Women's Movement have triggered what appear to be irreversible changes in women's and men's roles. Although this social experiment will take years to play out, when it is done it will offer new—perhaps even definitive—evidence about the relative roles of nature and nurture in producing the phenomenon we call gender.

Nurture: Amen! But I would like to amend one thing you just said.

Nature: What's that?

Nurture: When talking about gender research, never use the word definitive!

Nature: Finally, a point we can agree on!