Intersex persons are burdened enough by disputes about how discrepancies between their genotype and genitals should be handled. But their psychological makeup is also part of the battlefield on which the nature-nurture dispute is fought. To explain why, Rebecca Jordan-Young, in Brain Storm, cites experiments with animals that traced the effects of deliberate pre- or post-natal hormonal interference on their subsequent social and sexual behavior. Brain Organization Theory (BOT) researchers have used these findings to suggest that every mammalian brain (human included) "is a sort of accessory reproductive organ." In other words, along with differing gonads and other structures needed for heterosexual mating, "[m]ales and females also need different brains so they are predisposed to complementary sexual desires and behaviors that lead to reproduction."

As Jordan-Young summarizes:

This theory suggests that regardless of chromosomal sex, having a male-typical hormonal milieu in utero leads to male-looking genitals and "masculine" psychological traits, including erotic orientation toward women, as well as broadly masculine cognitive patterns and interests. Likewise, a female-typical hormonal milieu leads to feminine-appearing genitals and "feminine" psychology, including erotic orientation to men …. Moreover, sexual differentiation is not restricted to those behaviors that are directly involved in reproduction, or even in courting. Instead, brain organization theory is used to explain a very wide range of differences related to gender and sexuality—in humans, including everything from spatial [ability], verbal ability, or math aptitude, to a tendency to display nurturing behavior, to sexual orientation …. [T]he core assumption is that masculinity and femininity are package deals with reproductive sexuality at the core.

How well is the theory substantiated? To answer this, Jordan-Young reviewed over 300 studies, covering the various research designs used to test the hormone-psychology connections summarized above. She also interviewed almost two dozen prominent brain organization scientists. The result is a very detailed assessment, and one that could initially intimidate readers with little training in research design. But Jordan-Young is a clear and careful writer, so her book will repay persistent readers at all levels of methodological literacy. She is no Cartesian dualist: she clearly respects the constraints of embodiment in animals and humans alike. She also defends the freedom of scientists (of whom she is one) to use deterministic models to explain psychological and social processes, not just more obviously physical ones. But she thinks that BOT research is plagued by bad theory and shoddy methodology, often in the service of defending the theory in the face of ambiguous or contrary data. Ironically, despite the much-touted scientific trappings of their work, many BOT researchers routinely violate the central Popperian criterion for being scientific—namely, willingness to revise a theory when it is confronted by consistent empirical failures. Jordan-Young shows that some BOT adherents are also too quick to accuse their critics of blindly following the forces of postmodern political correctness, when in fact many are motivated by legitimate methodological concerns.

What are some of these concerns? Jordan-Young notes that when you can't do with humans the kind of controlled experiments that can be done with animals, you have to settle for a series of quasi-experiments, in which you look for consistent patterns of correlation across time and place, and across differing samples and research designs. There are rules for doing good quasi-experiments. For instance, we obviously couldn't establish a causal link between cigarette smoking and lung cancer by randomly assigning some people to smoke real cigarettes and others to smoke fake ones for several decades, then comparing their differential cancer rates. So epidemiologists did the next best thing: longitudinal studies tracking the health of existing smokers and non-smokers. (This is known as a cohort study design.) They also used the opposite approach: finding people who already did or didn't have lung cancer, then retrospectively assessing their rates of cigarette consumption. (This is known as a case-control design.)

The reason the smoking-cancer link is so well accepted is that, over the years, these quasi-experimental studies shared several important features. First, the "input" and "output" variables, i.e., "smoking" and "lung cancer"—were consistent, both in terms of what they represented and how they were measured over time. Second, the number of people studied was very large. Third, the smoking-cancer correlations showed up in different kinds of research designs (e.g., both cohort and case-control studies). Fourth, most of the correlations between smoking and lung cancer were large and statistically significant. Finally, and critically, there was a consistent "dose-response" relationship across all types of studies: more smoking, more lung cancer risk; less smoking, less lung cancer risk. (There would hardly have been a legal case against the cigarette companies if a significant percentage of studies showed that smoking a pack a day for years made no difference, or worse, even reduced the chances of lung cancer.)

Jordan-Young applies these quasi-experimental research standards to her hefty sample of studies designed to test BOT. She concludes that, far from pointing to likely causal relationships between "brain sex" and sex-typed behavior, both the theory and its research methods are in need of drastic overhaul. Consider, for example, the many studies that have tried to demonstrate more "masculine" personality traits, skills, sexual interests, and the like in females with the intersex condition known as congenital adrenal hyperplasia (CAH) than in the normal population of females. When these are taken together (and they must be: even the findings of a double-blind trial require at least one replication, and less-controlled quasi-experiments are held to an even higher standard), the evidence is thin. For example, there is no consistent evidence that CAH females have superior spatial skills, of the sort that help you orient yourself geographically or do jigsaw puzzles. In normal populations, there is a modest but statistically significant difference in some spatial skills that favors males. But when assessing CAH females or males most studies show no advantage, or (more embarrassingly) poorer spatial skills in CAH persons than in normal controls of their own genotype. This clearly violates the dose-response rule: just as you would expect increasing rates of smoking to correlate with increasing risks of lung cancer, so (according to BOT) there should be a positive correlation between people's prenatal and/or postnatal "doses" of testosterone and their scores on sex-related cognitive tasks. At the very least, the correlation shouldn't be reversed. Nor are CAH girls reliably more aggressive, assertive, competitive, or dominant than their non-CAH peers. Nor are they more likely than girls in general to engage in rough-and-tumble play as children, or to prefer male playmates in childhood, or seek out female sexual partners in adulthood. And all this is despite the fact that, having been born with masculinized genitals, there may be the expectation on the part of parents and others who know of their condition that they will be stereotypically more like boys. Remember, you can't do a double blind experiment when you're raising children.

There are two exceptions to these disconfirmations of brain organization theory. One is that CAH girls, compared to matched controls, are more likely to say they prefer so-called boys' toys, such as building blocks or vehicles, to toys like dolls or cooking sets. But here we run into two problems. The first is that what people say and what they do are often discrepant, and very few studies have looked at what toys CAH girls actually do play with compared to normal controls. A 2003 study that did so (in an individualized playroom setting) found that CAH girls were indeed more likely than others to play with a toy garage, cars, and Lincoln logs than with baby dolls. This was taken as support for a version of BOT that sees people with testosterone-organized brains as more likely to be "systematizers" (interested in how things are put together, both concretely and abstractly) than "empathizers" (interested in understanding other people). However, a closer look at the data shows that even the normal control girls spent three times as much time playing with the garage and cars as with the baby doll, and six times as much with the Lincoln logs. And at the end of the play period, when offered the choice of a doll, a car, or a ball to take home, they chose the doll least often, by a wide margin.

If you're wondering why, in 2003 (well after girls started playing soccer in droves), BOT researchers were coding "masculine" and "feminine" toys the same way they did in the 1950s, that's the second problem. It reflects the essentialist presumption that gendered behaviors, along with normal genitals, are parts of a fixed package, and so their measures can remain as unchanging as measures of genital anatomy. It presumes that normal girls with low testosterone can be only minimally influenced by cultural shifts to start preferring Lincoln logs to baby dolls (once an empathizer, always an empathizer), even when data gathered by BOT researchers themselves indicate otherwise.

In the face of such contradictions, Jordan-Young notes that some BOT researchers over the years have quietly changed their definitions of what is "natural." For example, the BOT view of "natural" female sexuality originally excluded things like masturbation, erotic dreams, and initiating sex, all of which were regarded as quintessentially masculine. These days BOT researchers treat all of them as "natural" for both sexes. But they did not make this shift because they suddenly admitted that cultural forces (for example, the second wave of feminism) might be stronger than they previously thought. Instead, they underplayed the changes they'd made to accommodate those very same cultural forces while continuing to embrace a biologically essentialist paradigm. The result is that current definitions of female sexuality are treated as equivalent to past ones for purposes of supporting the theory, when in fact they're like apples and oranges. It's like trying to establish a smoking-cancer link by measuring throat cancer rates for a couple of decades, then deciding to switch to lung cancer without acknowledging the switch or explaining why it was made. This is not the stuff of which successful lawsuits are made.

The second exception is that though CAH women don't engage in homosexual behavior more than other women, they are less likely to marry or express interest in men, and somewhat more likely to have same-sex erotic fantasies. BOT researchers take this to indicate that excessive testosterone has masculinized CAH girls' brains and hence their sexual preferences. But here we run into a vexing methodological confound. Most CAH girls who have been surgically "corrected" (as most now are) have very stressful medical histories. Surgeries often extend beyond infancy, followed by uncomfortable mechanical therapies to keep the reconstructed vagina open. Moreover, surgery can lead to reduced sensitivity as a result of clitoral reduction. If you add to this the fact that CAH girls are often recruited to be in research studies where their vaginas and genitals are frequently examined (and sometimes photographed) by male researchers, then you hardly need to invoke high testosterone levels to explain their relative lack of interest in men and marriage, or their occasional fantasies that they might be better off with another woman. Unfortunately, BOT researchers have shown little interest in doing well-designed studies to assess and then control for the psychological effects of such experiences.

Now You See It, Now You Don't: Enter the Social Psychologists

Jordan-Young's book is wide-ranging in its criticisms of the BOT paradigm, but the examples I've cited should be enough to show that she has done her homework. In the meantime, social psychologist Cordelia Fine (with her book Delusions of Gender) and neuroscientist Lise Eliot (Pink Brain, Blue Brain) have weighed in on the debate. These scholars focus less on BOT research that has been done with sexual minorities—such as intersex persons—and more on the claims made for males and females in general. If boys are more likely to be systematizers and girls to be empathizers, should you send your child to a single-sex school that takes these differences into account? If women's and men's brains are wired for complementary skills and interests, should we stop worrying that there aren't more tenured women scientists at Harvard? If your preschool son is slow to develop language skills, should you chalk it up to his masculine brain and let him wait a year longer than his sister to start kindergarten? If your teenage daughter struggles with algebra, are you doing her feminine brain a favor by letting her drop the class? Brain organization theorists (and many of their popularizers) often say yes to such questions, though sometimes, Fine notes, with a show of pained reluctance to demonstrate how objective they are.

If you're wondering where the second wave of feminism has disappeared in all this, Fine suggests that a covert anti-feminist backlash is at work. This is partly why she coins the term "neurosexism" as part of her book's subtitle: a new form of sexism that recasts what used to be enforced "duties" as simply natural (and therefore uncoerced) "preferences." So if, after decades spent dismantling gender discrimination, few women still choose to be engineers and few men choose to be kindergarten teachers, the fact that each of these jobs is skewed toward one sex (as well as being very unequally compensated) is said to reflect no injustice at all. Fine calls this "Gender Equality 2.0." It is "a revised version of equality in which men and women are not equal, but equally free to express their essentially different natures."

But social psychologists have ways of showing that gender discrimination is still happening, and that "essential" differences between the sexes can be quite responsive to social influence. Fine reviews this literature with a thoroughness laced with irony. Earlier I noted that we're not able to manipulate actual sex as an independent variable, or do double-blind experiments with humans to separate the effects of gendered socialization from gendered biology. But social psychologists have developed indirect ways of doing both. Consider, for example, the many experiments showing that the same (fictitious) job application is often treated quite differently depending on whether the applicant is male or female. The names of such "paper people" are kept as identical as possible (Michael vs. Michelle Miller, Edward vs. Emily Williams, etc.), and the applications are randomly distributed to judges, sometimes at real hiring destinations and sometimes in laboratory simulations of workplace settings. In addition, neither the recipients of the applications nor the people who analyze their judgments know what the study is about, so it's a true double-blind experiment, and one that's sometimes been done in real-life settings. One recent meta-analysis of several dozen lab versions of the experiment showed that, overall, men were rated more favorably than identical paper women for stereotypically masculine jobs (engineer, truck driver, etc.), and less favorably for stereotypically feminine jobs (secretary, home economics teacher, etc.) Gender prejudice is likely still operating in the workplace.

A second way that social psychologists manage to do true experiments is by the use of a technique known as "priming"—that is, making something like gender or ethnicity more salient for one group than another, then seeing what effects this has on their behavior, attitudes, interests, etc. For example, consider a typical experiment in what is called stereotype threat, defined as a realistic fear of being judged and treated badly in a setting where negative stereotypes of one's group are present. Women and men with similar college mathematics grades are randomly assigned to one of two groups to do a math test using Graduate Record Exam-type problems. Before they begin, one group is told they are doing the test for unspecified research purposes. But the other group is casually informed that men tend to do better on this test than women. Then we see how well each group—both pre-selected to include students with similar math grades—does on the math test. Neither the students nor the people (or machines) scoring their tests know the purpose of the study, so this is again a true double-blind design. Across many such studies, the only people who underperform as a group are the women who are told that women can be expected to do so. (When the study design focuses on Caucasians and African Americans rather than men and women, and the "threat" is to African Americans' competence, you get analogous results.) Oppositely, if you preface the test with the announcement that no sex differences in test performance have been previously found, then the women in that group often outperform all the others.

It's also possible to produce the same effect in white college males, whom you might expect to have more confidence in their innately superior mathematical skills. But when the pre-selected groups are Caucasian and Asian male students, and one of the groups is told that Asians tend to do better on the upcoming math test, it's the Caucasian men in that group (but not those in the group given the non-threatening introduction) who get significantly lower scores. Related research suggests that it's the anxiety triggered by the threat to one's own group's status that interferes with performance. "Most people facing a difficult and important intellectual challenge are likely to have a few intrusive self-doubts and anxieties," writes Fine. "But people performing under stereotype threat have more. This places an extra load on working memory, to the detriment of the cognitive feat you are trying to achieve." To the extent that women must cope with such culturally presumed handicaps more than men (or blacks more than whites), they are vulnerable to performing below their actual capacity. But as the stereotype threat studies demonstrate, the ease with which this effect can be socially inflated, or even reversed, suggests that it has little to do with hormones.

These studies illustrate what Fine calls the "now you see it, now you don't" quality of supposedly gender-typical behaviors. Other examples could be cited.[1] Cumulatively, they suggest that gender operates like a verb as much as a noun. It's not just something we have (like hormones); it's something that we do, with greater or lesser zeal, depending on situational demands. Or, to change the metaphor, gender (along with ethnicity, religion, class, and other aspects of our human identity) is like a rheostat that we turn up or down, depending on how much or little we are "primed" to do so. And gender—perhaps because it is more dichotomous than ethnicity, class, or religion—is a very fundamental and anxiety-provoking part of human identity, so it can often be primed more easily. Thus, if the items on a questionnaire—even an anonymous one—let us know we're being assessed for empathy, women and men will both tend to skew their responses to line up with expectations for their sex. It's like a gender placebo effect: We think, therefore we are. But the fact that this difference disappears when people don't know what they're being assessed for suggests that empathy is a more generically human trait than BOT popularizers would have us believe.

Of the books considered here, Lise Eliot's misleadingly titled Pink Brain, Blue Brain is the one most obviously aimed at a popular (but educated) audience. Though the title smacks of BOT orthodoxy, its subtitle—"How Small Differences Grow into Troublesome Gaps—and What We Can Do About It"—points to a more nuanced agenda. Eliot is a medical school professor of neuroscience who does research on neuroplasticity—that is, on ways that experience changes the brain. Even so, she began writing the book with a bias toward brain organization theory. Thinking that she could explain human behavioral differences by building mostly on animal research, she soon found herself accepting the more social constructionist arguments presented by developmental and social psychologists. Like Fine and Jordan-Young, she lists the flaws in the BOT paradigm, including some that the other authors missed. For example, Simon Baron-Cohen's version of BOT includes the hypothesis that autistic boys (who often display a compulsion to collect and organize) have brains that have been hyper-masculinized in utero. If so, you'd expect boys who are diagnosed with autism to have had higher prenatal testosterone levels than those who are not. But this turns out not to be the case—nor is there any correlation in girls between prenatal testosterone levels and their later levels of "empathizing" vs. "systematizing" behavior. Another dose-response embarrassment.

Eliot also reminds readers that gendered behavioral differences are far from absolute. A small average difference between the sexes (e.g., in spatial or verbal skills) is usually dwarfed by the amount of variability within each sex—hardly a ringing endorsement of gender essentialism. And even when average differences are found, this indicates nothing about their origins: correlation is not the same as causality.

Nevertheless, Eliot is inclined to give BOT some benefit of the doubt, and grant that small gender differences at birth may reflect the work of prenatal hormones or other biological forces. For example, even in countries with superior medical services, boys are more vulnerable than girls to miscarriage, to be born prematurely, and to die at birth. Those that survive are on average fussier than infant girls—perhaps because of their prior vulnerability. Eliot also lists some reliable but small neonatal differences in olfactory, auditory, and visual sensitivity, as well as in motor performance, and notes that through mid-adolescence girls' bodies (including their brains) mature earlier than boys'. But she argues that these minor differences are greatly inflated by the different social demands, expectations, and resources placed before girls and boys—rather like a snowball that begins tiny, but gathers size and momentum as it rolls down a hill.

The human brain, Eliot concludes, has much more plasticity than people give it credit for. This blind spot is especially significant in the United States, where people routinely attribute their own and others' achievements to innate ability rather than to hard work. By contrast, in the rising Asian nations and in many European ones, it is assumed that if children work hard enough and are well taught, they can all be competent in all subjects. Not coincidentally, both boys and girls in these nations routinely become bi- or multilingual, and on international mathematics tests their female students often leave American males (with their "innate" systematizing edge) in the dust. "Gender," Eliot asserts, "should never be an excuse for a child's low performance in a given area, whether it is reading or math, science or writing. Expectations are important, so we must hold them consistently high for all children."

Eliot fleshes out this assertion with practical advice for parents and teachers. For example, children of both sexes obviously need both language and spatial training—but make sure you don't shortchange boys on the former, or girls on the latter. Look for competent, same-sex role models to build up boys' empathizing and girls' systematizing skills. Emphasize coed sports and coed groups for school projects, to get around children's tendency to form same-sex huddles and thus reinforce gender stereotypes. Never mind whether the stereotypes originate in nature, nurture, or both: remember neuroplasticity, and challenge them. "Every boy and girl," Eliot writes, "deserves the chance to develop the full range of his or her potential, unhindered by gender, race, or other societal assumptions. If we can pull it off … [b]oys and girls will both lead richer lives, and our society will benefit from their [more] complete development."

Caveat Emptor: Where Do We Go From Here?

At the end of Brain Storm, Rebecca Jordan-Young recalls an assignment in which she was asked to analyze a sex survey done by a popular magazine. The findings actually challenged the popular stereotype that men are mostly interested in sex, while women mainly crave relational intimacy. But her editor kept steering her away from this data and back to the familiar dichotomy: "When he finally said to me, 'People don't buy this magazine to learn something; they like to confirm what they already know,'—I knew it was time to withdraw from the project." Eliot and Fine join her in documenting a gap between actual BOT findings and the rhetoric of the theory's enthusiasts. Eliot cites one of these, Leonard Sax, who uses the minuscule auditory threshold differences between boys and girls to warn that teenage girls hear their father's voices as "ten times louder" than they actually are, and goes on to claim this as a reason for steering boys and girls into single-sex classrooms. Another BOT popularizer, Louann Brizendine, dramatically blames the prenatal "testosterone marination" of men's brains for their "innate [in]ability to read faces and tone of voice for emotional nuance."[2]

In the face of such wild generalizations, one might be forgiven for wanting to fire all (or most) of the writers who make money exploiting people's gender insecurities and their reflex awe of (what they take to be) science. Of course there is nothing new about this, and scientists have regularly held that they are not responsible for popular distortions of their work. But when it comes to bridging the evidence gap between animal and human studies, scientists have a special responsibility to be clear about the methodological ambiguities that surround their work, including all the challenges of doing good quasi-experiments. Research design is not a very sexy subject, but there are good practical reasons for encouraging greater literacy about it. A wise dean at one of America's top universities recently welcomed a new medical school class by warning them that half of what they were going to be taught would turn out to be false. Unfortunately, he added, we don't know which half. Buyer beware.

A second lesson—stressed by all the working scientists in this review—is that many BOT researchers (and just as many in the social-constructionist camp) have a too-simplistic view of how nature and nurture work. Many embrace what might be called the layer cake model: they talk as if either nature or nurture is more foundational, then concede that the other factor might add or subtract a bit from its effects. This reflects a common temptation to believe that we can neatly separate the two—as gender studies scholars did back in the 1970s, when they decided that the term "sex" should refer to what was strictly biological, and "gender" to what was strictly cultural. Unfortunately for the layer cake model, gender affects sex, and sex affects gender—which is precisely why I have avoided using this terminological distinction. Think of the anorexic who is so influenced by cultural messages about women's bodies that she ceases menstruating when her weight gets too low. Think also of the boy in our culture who enters puberty early, and is immediately assumed by older teenagers to be ready for sexual initiation, whether he wants it or not. In another culture he could instead be forbidden even to be alone with any female who was not a close relative.

So "sex" and "gender" form a feedback loop with each other. The brain and the rest of the body constrain experience, but experience is at the same time constantly changing both. It can even alter the expression of genes that are passed on to children and grandchildren, as the emerging field of epigenetics has begun to notice. Yet as recently as a decade ago, the idea that acquired traits could be biologically passed on to future generations was treated as a Lamarckian myth decisively laid to rest by the advances of modern genetics. We need to think less in terms of essences, and more in terms of developmental potentials. We need to pay due attention to brain plasticity.

Along the way, Jordan-Young suggests a couple of other ways of thinking outside the box. First, we need to rethink how we talk about the so-called "sex hormones." Not only are they not specific to males or females; their effects aren't even limited to reproductive processes. They have also been found (thus far) to influence liver and bone growth, nitrogen and carbohydrate metabolism, and diurnal body rhythms. The "sex hormone" framework, she concludes, "demonstrably blocks recognition of complex and accurate information … [and] what good is a science that doesn't tell us anything new?" Second, while it's clear that personality traits and interests are not the same in everyone (even in infancy), "they are also not well captured by the binary system of gender—even in spite of pervasive [cultural forces] that exert pressures toward this pattern. We aren't blank slates, but we also aren't pink and blue notepads." Identity emerges from a host of influences, including class, ethnicity, politics, religion, and many others.

All of this strongly suggests that Christians should not be allowing the BOT tail to wag the ecclesiastical dog, in terms of church policy regarding so-called homosexuals or any other gender-related issue. This is certainly—but not only—because the gap between BOT rhetoric and its actual scientific rigor is often weak. Just as certainly, Christians should be cautious about jumping on the social-constructionist bandwagon, despite its much-needed challenge to BOT's biological determinism. Both camps have important lessons to teach us about embodiment and identity formation—and hence about pastoral responsibility to sexual minorities of whatever kind. But getting stuck in this debate can tempt onlookers to lurch between reductionism and self-deification: between the notion that Christian tradition should yield either to biological necessity (so called) on the one hand, or to shifting individual identity choices (so called) on the other.

The late Reformed theologian Lewis Smedes once pointed out that biblical anthropology does not envisage us as Cartesian angels driving around in automobiles that yield to our disembodied wills. Nor does it conclude that we are merely brains in vats, subject entirely to natural (and/or social) forces beyond our control. Instead, he wrote, we are bodies who come alive—or do not—to God. This means that whatever impulses we have, regardless of where they originate or how socially respectable they are, we can all expect to face major renovation plans. The church has not always done a good job of deciding what this implies for sexual ethics on the one hand and pastoral responsibilities to sexual minorities on the other. But it's simply false to assume that it has never really had to grapple with such issues till now: both the biblical record and the church's early attempts to deal compassionately with eunuchs indicate otherwise.

On the other hand, it bears pointing out that even the churches who are most conservative on the issue of homosexual practice have long since stopped being biblical literalists on the issue of divorce—so much so that the rate of divorce among the self-identified "born again" is no different from that of the U.S. population at large. Those who believe that heterosexual monogamy and celibate singleness are the patterns to which God has called us cannot blame gays and lesbians (however those terms are defined) for their own failure to keep their marital promises. And here is another irony: members of the very demographic group (upper-middle class) who led the no-fault divorce stampede in America forty years ago are now the least likely to divorce. They are more often staying together, raising their children together, getting their kids into better schools (students in élite colleges are considerably less likely to come from divorced families than the student population at large)—and, to the shock of Enlightenment secularists, starting to go back to church.

Neither divorce nor one's choice of sexual partner may be strictly confessional issues—but they are both surely prudential issues, and forty years after the divorce revolution began, people are beginning to recognize that, absent things like chronic abuse or irresponsibility, marital commitment trumps serial monogamy as a route to human flourishing for adults and children alike. Similarly, forty years after the sexual revolution was launched, both the heterosexual majority and the so-called sexual minorities are beginning to acknowledge its exploitative downside. So rather than rushing to rubber stamp cultural trends that are already in the process of changing, perhaps the church—while surely being attentive to pastoral and practical needs of the marginalized—needs to remind all of its members that their identity in Christ is foundational to all other identities, and that this will let no one off the hook in terms of what it will require. Perhaps we should think of this as heart plasticity.

—This essay is part 2 of a two-part article.

1. An excellent review of the meta-analytic literature on this topic can be found in Janet Shibley Hyde's "The Gender Similarities Hypothesis," American Psychologist, Vol. 60, No. 4 (2005), pp. 581-92.

2. Louann Brizendine, The Female Brain (Broadway, 2006), p. 166.

Books discussed in this essay:

Lise Eliot, Pink Brain, Blue Brain: How Small Differences Grow into Troublesome Gaps—and What We Can Do About It (Houghton Mifflin Harcourt, 2009).

Cordelia Fine, Delusions of Gender: How Our Minds, Society, and Neurosexism Create Difference (W. W. Norton, 2010).

Rebecca M. Jordan-Young, Brain Storm: The Flaws in the Science of Sex Differences (Harvard Univ. Press, 2010).

Mary Stewart Van Leeuwen is professor of psychology and philosophy at Eastern University in St. Davids, Pennsylvania.

Copyright © 2012 by the author or Christianity Today/Books & Culture magazine.
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