Since the 1970s, feminism and equal-opportunity legislation have promoted the expectation that greater gender equality in America will result in women’s choices looking more like men’s. This both has and hasn’t happened. Women have flooded into universities and the workforce; in graduate programs and law and medicine, they have equaled or surpassed the number of men. But as writers such as Lisa Belkin and Judith Warner have argued in a series of attention-grabbing articles and books, many young, university educated women are choosing family over work. And when it comes to computer science, physics, or engineering, female interest appears to have hit a plateau, and women remain a stubborn minority.

These statistical asymmetries are often cited as proof that sexual discrimination is still pervasive, however nebulous its current form. But in her new book, “The Sexual Paradox” (Scribner, 356 pages, $26), the developmental psychologist Susan Pinker suggests that this professional imbalance is neither accidental nor culturally prescribed. Comparing working women in countries of relative affluence and stability, such as America, Britain, and Germany, to their counterparts in the Philippines, Russia, and Poland, Ms. Pinker found that those living in less prosperous economies are significantly more likely to enter such typically masculine fields as physics and engineering. In other words, assimilation feminism is not a cry for equality but a cry of necessity, and the more options available, the greater the contrast will be between the professional choices of women and men.

Ms. Pinker believes that these ongoing disparities are more a product of innate gender differences than discrimination. We can’t know that the failure of women to match the professional choices and achievement of men is a political failure, she suggests, unless we know it is a function of the political culture. In her book, she sets out to “examine the science” of sex differences, to stand back from the politics of the issue and allow empirical data an unclouded voice.

It’s inappropriate, Ms. Pinker writes, to regard men as the generic standard against which women should be measured. For one thing, men are an extremely heterogeneous group; there is greater variability among men than women, and boys are much more likely to struggle in school than girls. Autism, ADHD, dyslexia, and conduct disorders are all significantly more common among boys; likewise, men are significantly more prone to a variety of diseases, risky behavior, violent crimes, and younger deaths. Men are not a model of anything, in other words, so much as a model of everything.

Here, she borrows the claim made by Simon Baron-Cohen, that Asperger’s syndrome, a high-functioning form of autism, represents the “extreme male brain.” Those with Asperger’s syndrome (90% are men) are often completely focused on predictable, systems-based information, and severely limited at detecting emotional and social cues. Despite these limitations, many people with Asperger’s syndrome are able to harness one talent that allows them to master a particular field or professional niche. Their single-minded interest is what enables their success. Just like men. Women, of course, are different, and the tendency to see them as “stymied versions of men leaves the large numbers of capable women who don’t fit the male model cast in a familiar, infantilized role,” Ms. Pinker writes. “Somehow, despite their achievements, they’re seen as unable to decide for themselves.”

But decisiveness isn’t the issue: On their own, women are unlikely to share the same professional goals as men, Ms. Pinker suggests. Women and men have different brains from the start, she writes, and women are much less likely to pursue a subject or skill to the exclusion of all — and everyone — else. In the brains of male fetuses, the presence of testosterone impairs the development of the more vulnerable left hemisphere; the right hemisphere compensates, making men more literal-minded than women, and limiting their ability to communicate emotionally.

These differences serve, in part, to explain why women are more likely to be empathic than men — and susceptible to empathy’s consequences. Ms. Pinker points to evidence that the densely networked brains of women respond more intensely to the emotions of others, and that women produce more of the feel-good hormone oxytocin, which results from and therefore promotes nurturing behavior, attachment and intimacy. Forming bonds with spouses, children, and friends actually feels better for women than it does for men.

Throughout her book, Ms. Pinker emphasizes her approach of standing back to let “the science” speak for itself. She invokes findings from neuroscience, psychology, economics, anthropology and biology — to name just a few of her sources. And to illustrate the mismatch that many women feel between their values and the ones espoused by their corporations or law firms, Ms. Pinker introduces us to a series of women who have given up their powerful careers. But, troublingly, she doesn’t discuss the motivations of a single one who has stayed. Where is Secretary of State Rice in this supposedly empirical roundup? Or Senator Clinton? Where is the line between anecdote and evidence?

There is indeed something problematic about Ms. Pinker’s use of information, her mixture of journalistic style and scientific method. At times, the data she stacks up seem distinctly handpicked, and her selective use of data is particularly troubling in light of her reliance on neuroscientific findings. These tend to speak with a particular authority, amplified by most readers’ unfamiliarity with the field. Neuroscience may one day prove or refute the ideas we have about ourselves, but most neuroscientists would agree that that day is not here yet. Rather than attempting to force science into ready-made conclusions, perhaps some deference is due to the mysteries we still have, if only to be in a better position to solve them, when and if the answers do come.

Ms. Schwartz is a graduate student in neuropsychoanalysis at Yale University.