Pink Brain, Blue Brain: How Small Differences Grow into Troublesome Gaps—and What We Can Do About It

Determined to figure out how much of my toddlers’ divergent behavior is based upon innate gender difference, I read Cordelia Fine’s Delusions of Gender and the first 100 pages of Lise Eliot’s Pink Brain, Blue Brain (the introduction and chapters covering prenatal development and infancy, since both authors agree that these periods are key to determining whether only nurture is to blame for pre-pubertal differences between boys and girls). Though the two writers agree on just about every scientific point relevant to this inquiry, their framing diverges wildly. Fine reviews the evidence and concludes that science does not support the assertion that any gender difference in behavior or preference is hard-wired.

Eliot’s presentation baffles me. As the subtitle of her book makes clear, she concludes that “small” differences in “interpersonal skills, such as aggression, risk taking, and competitiveness . . . germinate from basic instincts and initial biases in brain function.” Each time she introduces or summarizes, she recites a similar assertion: “[N]ature sets the ball rolling, biasing boys and girls toward different interests and behavioral styles even before they’re born.” And yet, in the nitty-gritty discussion of each potential hard-wired “difference,” she concludes as Fine does, that the evidence is entirely lacking. It’s almost as if she titled the book first and then wasn’t able to change her frame of mind after sorting through the data. Or as if she wrote the individual sections at the office, and then penned the concluding and introductory bits at home while sleepy or drunk, allowing her own subconscious bias to sneak into the manuscript.

Eliot herself writes, “what I found, after an exhaustive search, was surprisingly little solid evidence of sex differences in children’s brains. Sure, there are studies that do find differences, but when I looked closely at all the data . . . I had to admit that only two facts have been reliably proven. One is that boys’ brains are larger than girls’ . . . [in] conspicuously similar . . . magnitude to males’ greater height and weight at birth and in adulthood. The second reliable fact is [a] difference that shows up around the onset of puberty.”

She continues:

If you’ve read anything about boy-girl differences, you’ve probably become convinced that scientists have discovered all kinds of disparities in brain structure, function, and neurochemistry—that girls’ brains are wired for communication and boys’ for aggression; that they have different amounts of serotonin and oxytocin circulating in their heads; that boys do math using the hippocampus while girls use the cerebral cortex; that girls are left-brain dominant while boys are right-brain dominant. These claims have spread like wildfire, but there are problems with every one. Some are blatantly false, plucked out of thin air because they sound about right. Others are cherry-picked from single studies or extrapolated from rodent research without any effort to critically evaluate all the data, account for conflicting studies, or even state that the results have never been confirmed in humans. And yet such claims are nearly always presented to parents, with great authority, as well-proven and dramatic facts about boys’ and girls’ brains . . . . [O]ne particularly insidious way in which neuroscience has been misused . . . is the idea that the brain’s sex differences—most of which have been demonstrated in adults only—are necessarily innate. Ignoring the fundamental plasticity by which the brain learns anything, several popular authors confuse brain and nature, promoting the view that differences between the sexes are fixed, hard-wired, and predetermined biological facts. . . .

She also rejects the idea of “differences between the sexes in sociability and emotional expression” at birth, explaining the evidence showing that they arise in infancy (and debunking the one study often cited for the proposition that girls are “innately more people oriented than boys are”). She concludes that the differences that begin to arise at about four months of age likely originate from the divergent way caregivers react to emotional expression in male and female babies rather than any hard-wired difference. “Dozens of . . . gender-disguise studies confirm that people judge babies differently based on what sex they believe the babies are and regardless of the real sex under the diapers. In addition to rating babies’ expressions and physical appearances differently, adults tend to choose different toys for each sex . . . and to engage them differently-interacting in more physical, expansive ways with boys and more nuanced, verbal ways with girls.”

She also quite reasonably concludes: “Does the neonatal testosterone surge . . . shape human boys’ development? We don’t really know . . . .”

And even after nurture has gotten ahold of babies and created “reliable” differences by around age two, she reminds us that “[t]hese differences are . . . really quite small.” For example, “Compared to the overall range of language ability in young children, the average difference between girls and boys is tiny, accounting for just 1 to 2 percent of this total variance. Consequently, you can find many boys who are more verbal than the average girl, and lots of girls who are less verbal than the average boy.”

All of this is perfectly rational and overlaps precisely with Fine’s interpretation of the evidence. And yet, in another spot she writes, “There are, to be sure, a few truly innate differences between the sexes—in maturation rate, sensory processing, activity level, fussiness, and (yes!) play interests.” To see why this statement is utterly confounding, let’s unpack each of these areas of research.

When discussing maturation rate, Eliot cites boys’ slight delay in respiratory development, nothing brain or behavior related at all. Which explains why she doesn’t mention it in her meta-summary stating that the only proven difference is brain size.

Her discussion of sensory processing boils the differences down to extraordinarily slight discrepancies in hearing (so small that the newborn screening doesn’t differentiate between the sexes) based mostly upon the larger size of boys’ skulls. She concludes: “[A] close look at the research on sensory differences in newborns reveals that they are small and of little relevance to children’s learning. . . . It’s therefore disingenuous to suggest, as Leonard Sax does in his book Why Gender Matters, that ‘these built-in gender differences in hearing have real consequences.’”

As for activity level, she states that there is no evidence of gender difference in activity in the womb, and that boys and girls show no statistically significant difference in gross motor development in infancy. Her only reasoning supporting any discrepancy is convoluted at best: she figures that boys “excel [at] gross motor development [because they] sit[], stand[], and walk[] at the same ages as girls in spite of their overall slower maturation.” In other words, male and female babies reach the same milestones at the same time, showing no difference in activity level until after infancy. Later divergence is ascribed to the fact that adults “aware of physical differences in older boys and girls, set up different motor expectations for their sons and daughters, even in infancy.” This is all in her own words.

When it comes to fussiness, she “raises a crucial issue . . . : whether differences in sensory responsiveness, fussiness, . . . and so on are truly innate or are a consequence of boys’ suffering from their recent circumcisions. Surprisingly little of the research has controlled for this important variable.” She also states, “[T]hese differences have mostly been described by examiners who weren’t blind to the sexes of the babies, and some studies have failed to detect any sex differences in newborn irritability or consolability.” So fussiness is an innate difference, to be sure, except it’s not, ’cause we’re not at all sure.

Finally, she says that the only data regarding play interests show that there is no discrepancy in them whatsoever until after plenty of time for caregiver influence.

Thus the conclusion that these are “a few truly innate differences between the sexes” makes absolutely no sense in the context of her own research and writing.

Her recommendation that parents “[t]alk to your babies, especially boys” and her reference to “girls’ less active tendency,” also come out of nowhere, unless of course she’s talking about the period after infancy when this approach/description may be necessary/accurate to counteract nurture—but then she really ought to say that.

Unfortunately, Eliot’s inconsistent description of her own research in these first two chapters made me doubt her objectivity too much to warrant finishing the book.

As for stars, I’m at a bit of a loss. The book seems quite well-researched and provides an impressively smooth read for such a complex topic. On the other hand, Eliot’s inability to keep her subconscious gender bias from infiltrating the first 100 pages is a real deal-breaker. I’m crossing my fingers that with a little distance from the text Eliot will see the inconsistency and remedy it in the next edition.


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