Men’s brains weigh about 2.5 pounds. Women’s brains are 100 grams less, the equivalent of one teaspoon. To most people, this difference seems negligible–hardly the stuff of controversy.

Scientists have yet to determine the reason for the size differential. Neuroscience is still in its infancy, and it will likely be many years before researchers gather enough evidence to tell us. In the mean time, most have adopted a common sense explanation: women are typically smaller than men therefore their brains are smaller. But if you spend enough time reading about neuroscience, you’ll inevitably stumble on alternative theories. Theories posited by men who believe that this teaspoon full of grey matter is proof of the superior male intellect. Men who contend that this missing bundle of neurons accounts for everything from the scarcity of women in science and engineering, to their wives inability to read maps.

Case in point, Terence Kealey, Vice Chancellor of the University of Buckingham in England.

Kealey recently published an editorial in the British newspaper, The Times, positing that women have smaller brains because they have been “domesticated.” For evidence, he relies on the findings of a Russian geneticist named Dmitri Belyaev.

In the late ’50s, Belyaev set about taming foxes. He started with a group of wild animals. From each subsequent litter of foxes, he chose the friendliest pups. “After 35 generations he produced animals that had been transformed from the usual snarling fearfulness of wild foxes into animals that were similar to domestic dogs.” (Why is a woman’s brain smaller than a man’s?)

What can this possibly tell us about the human female? Well, Belyaev found that tame foxes had smaller brains. Based on these findings, Kealey leaps to the conclusion that:

. . . women’s brains are smaller than men’s because, over the millennia, we men have been selecting friendly women with whom to breed. And that therefore we have domesticated them.
(Why is a woman’s brain smaller than a man’s?)

But Kealey goes on to undercut his own argument by pointing out that archaeological evidence shows that the skulls (and presumably brains) of both men and women have shrunk considerably over the past thirty thousand years. If domestication is responsible for our diminishing craniums, it seems to cut both ways.

Kealey doesn’t let faulty logic get in the way of making his point, however, which is – not surprisingly – that men are inherently smarter than women. As evidence, he cites a much-contested study by Paul Irwing of the University of Manchester, who claims brain size correlates with intelligence, because “more men have very high IQs than women.”

Kealey admits “IQ tests remain so controversial and so subject to cultural factors that we will need another half century before fully understanding them.” And that we “simply do not know enough about our brains to draw safe conclusions from any of these observations.” But that didn’t stop him from publishing his theory of “female domestication” in a major British newspaper.

I notice that Kealey makes no mention of studies that indicate that women have more gray matter tucked away in their gyri and sulci, the neuron-rich “wrinkles” on the cerebral cortex. (55.4 percent as compared to 50.8 percent in men.) (Serendip) Nor does he discuss experiments that suggest that the female brain compensates for its smaller size by having a higher density of neurons. ( Apparently, he found an outdated study of fox brains more compelling.

In fact, he seems quite taken with foxes. He also discusses a recent study, conducted by Brian Hare of Harvard University, which showed that domesticated foxes were more adept at reading social cues. Based on this study, Kealey extrapolates that small brain size may “optimize emotional intelligence.” Take heart ladies, you may be incapable of “[scaling] the same intellectual heights as men,” but you’re good with people, Kealey seems to be saying.

If smaller brains do, in fact, prove to enhance social skills, then women are hardly the only beneficiaries. Men’s brains have been shrinking over time as well. Kealey fails entirely to address the idea that this might be an evolutionary adaptation. As we become increasingly civilized, we may be shedding the primordial regions of the brain necessary for survival in the wild. If Kealey rejects the notion that women’s brains are smaller due to their physical size, then this would imply that they are simply more highly evolved than men. This is pure speculation, but so is the bulk of Kealey’s article.

Of course, this kind of leap of logic wouldn’t serve his ultimate purpose, which is to buttress notions of male superiority. Kealey’s dubious claims are based more on wishful thinking than science. He’s making a mountain out of a molehill–or in this case, a teaspoon full. And I, for one, sincerely hope that he meets the same fate as fellow misogynist Lawrence Summers.


  1. #1 Anne Milet
    January 16, 2007

    This is a fascinating controversy, thanks. I understand that several male neuroscientists and psychometricians have claimed that there are twice as many men with IQs above 120 than women. Something about increased male variance in IQ distribution? More morons and more geniuses, or something like that. Have you looked into that, or is it just more misogyny of male scientists?

  2. #2 albatross
    January 22, 2007

    The claim I’ve seen is that the variance of IQ is higher in men than women, which leads to more men at the high and low ends of the distribution. I’m not sure what the mechanism for this is supposed to be (maybe intelligence-linked genes on the X chromosome?)

    Out of curiosity, why did you switch between pounds and grams in the first paragraph? I think the difference in mass (from just doing the calculation) is about 9%. Presumably, that’s not too significant (women average about the same IQs as men, but different sizes of brains which had an effect seem like they would change the average for men vs. women), but I found it annoying that I had to do the calculation to get the difference in averages in the same units as the average mass of the male brain.

  3. #3 stewart
    January 28, 2007

    A few things –
    First, 100 grams difference is about 3.5 ounces, more than a teaspoon but well within the variances of either sex.
    Second, I looked at the data I have. Looking at men and women with 16 or more years of education, mean IQs are essentially identical (111 vs 112), and so are standard deviations (13 vs 13.5). So – no meaningful difference in means, no meaningful difference in standard deviations. Given that,in the US, more women than men are starting to attend university, can we expect that soon we’ll have ‘researchers’ claiming that women are obviously more intelligent than men?

    An annoying fairy tale disrupted by data – hurrah for data.

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