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Sep 172009
 

I went to an interesting talk today, one of Indiana University’s themester activities. Steven Gaulin of UC Santa Barbara spoke about work he has done with William Lassek on the relationship between human brain size and sex differences in fat distribution. It’s a fascinating story. We women are fattier overall than men, and we tend to carry our fat in different places. One thing the sexes have in common, however, is that fat is vital to the brain, the dry weight of which is mostly fat. Could the differences and the similarity be linked?

Gaulin presented several lines of evidence suggesting that fat deposited on women’s hips and thighs provides the material needed to build the unusually big brains (as primate brains go) of their offspring. He also suggested that a link between lower-body fat and cognitive ability in one’s offspring might have driven male preference and thus sexual selection for a low waist-hip ratio (WHR, i.e., the bottom half of an hourglass figure with small waist and large hips).

Among the things he discussed is something called maternal depletion, evident in hunter-gatherers but also more subtly observable in American women, in which the amount of hip/thigh fat decreases as women bear more children. Another factor is a link between WHR in women and cognitive ability (the data they used showed a link between lower WHR—i.e., more lower-body fat—and higher cognitive abilities in their offspring). Menarche (the onset of menstruation in young girls) appears to be related not to the amount of body fat but to its distribution (specifically, a greater amount of it on the hips).

Other lines of evidence include the fact that hip/thigh fat is very hard to get rid of; the body seriously taps into it only during the last trimester of pregnancy and during lactation. Also, hip/thigh fat and abdominal fat (the kind men are more prone to carry around) have opposite effects on the body’s supply of two long-chain polyunsaturated fatty acids that are crucial to brain development, docosahexaenoic acid (DHA) and arachidonic acid (AA). As best I could understand it—I’m not a biochemist, so I’m speaking fairly broadly here—the former promotes and the latter hinders the synthesis of these two fats.

I can’t possibly do justice to the entire talk here. In a nutshell, the shape of women’s bodies could be intimately connected, in interesting ways, with the need to nurture the development in babies of these unusually large brains we have. You can check out Gaulin’s web page for more information, including links to papers about the maternal depletion and menarche research.

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Mar 062008
 

A new fMRI study of 62 children suggests that the early lead girls have in language skills on average is based on differences in how language is processed in boys’ and girls’ brains. In the girls, the language-related areas of the brain were more active than in boys while they were completing spelling and writing tasks. Also, their performance correlated more strongly with this activity, which is also linked with abstract thought, than the boys’ performance did. In boys, performance depended more on the relevant sensory processing–sight for reading words, hearing for words. It’s not clear yet why this should be, or if it extends into adulthood, but these results and any followup studies might have some useful information about how to teach reading and writing.

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Nov 292007
 

This press release from Duke has some surprising news about a common variant of a gene that affects the availability of serotonin in the brain. Women who had experienced significant stress at some time in their lives and carried a shorter form of the gene showed more signs of depression than women who had the longer variant or were not stressed, but for men it was the long variant that was associated with more symptoms of depression, and the short variant was linked to fewer symptoms. The two sources of stress the study looked at were growing up poor, or caring for someone with Alzheimer’s disease or another form of advanced dementia. (I.e., they didn’t necessarily have to be current stressors.) I’m assuming the gene in question is SLC6A4, which encodes for the serotonin transporter (SERT) protein. (If you’ve heard earlier news about a gene related to serotonin transport being linked with depression, that’s the one.) This story gives an interesting twist to the fact that genes by themselves do not tell the whole story of who we are and how we work; environmental factors are also part of the story.

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Nov 082007
 

The stereotype is that women are the big talkers of the human species, but a recent set of meta-analyses of past research contradicts the stereotype. Overall men tend to talk a bit more than women, but the difference is small. In general, who talks more in a given situation depends on the context and the conversational partner(s). The analyses also looked at the purpose of conversation, finding that there is a difference in how men and women communicate with strangers (men more often strive to influence, women to connect) but with people they’re close to, the difference vanishes. This press release on EurekAlert is short but it has some more details. The basic message seems to be that it appears to be society rather than biology that shapes who talks how much when.

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Who looks at what

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Apr 132007
 

I’ve volunteered for a number of studies that people in the psychology department at Indiana University were working on, and also for a few that were being conducted by the Kinsey Institute. The psych experiments seem to involve a lot of time in tiny rooms watching words or photos flash by on a computer screen, and for the Kinsey studies I just filled out questionnaires. It’s all been interesting to one degree or another, but somehow I missed the chance to have my eye movements tracked while I looked at what my grandmother might have called naughty pictures.

A researcher at the Kinsey, working with a colleague at Emory, examined the way men and women react to sexual images. As a followup to an earlier study that looked at brain activity in men and women who were exposed to sexual stimuli, the researchers monitored eye motions while subjects looked at sexual photographs. The results were perhaps not what you would expect: The men in the study were more likely to look first at a woman’s face than the women were, and the men spent more time looking at the faces. Men and women spent comparable amounts of time looking at genitals, while women looked longer than the men did at pictures of men and women having sex. Being on the pill seemed to make a difference. Women who were on hormonal contraceptives were more likely to look at genitals, while women not on the pill looked more at aspects of the images that provided context. The earlier brain activity study found that men showed greater activity in the amygdala when exposed to sexual stimuli than the women did. It’s still not clear what all the pieces add up to, but it’s an intriguing set of results anyway. You can read more about it in this press release from Science Daily.

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Dec 042006
 

I am, therefore I walk. Or is it “I think, therefore I walk”? Or maybe it’s more like “I walk, therefore I think.” At any rate, I walk a lot, to work, to the library, to concerts on campus, and I enjoy the ambulatory lifestyle. So I was very interested in this article about some research into what our gait says about us, individually and collectively. The article describes the work of the Biomotion Lab at Queen’s University in Canada, where people don a nifty outfit that abstracts their motion into a pattern of moving lights that evidently provides a surprising amount of information about gender, mood, and mental state. If you visit the Biomotion Lab’s site and click the “demos” link, you can see some examples, including an animation of a walking figure that you can adjust to make it more masculine or feminine, happier or sadder, etc. You can also take part in an online experiment that examines how well people can identify gender from a person’s gait. The article also covers some bigger-picture work at the lab, including studying our ability (which we share with other animals) to identify the presence of other living beings by their footfalls. It’s really interesting to me that our brains do all kinds of complicated processing to extract a lot of information from the motions of living things, particularly other people, but we’re not consciously aware of it and have a hard time figuring out how it all works.

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Aug 082006
 

So how different are men and women really? This article from The Economist examines some of the latest research into sex differences in behavior, concluding that they are real but often not easy to interpret and in many cases smaller than imagined. Of particular interest was an analysis of “all the important meta-analyses that have been conducted on differences between the sexes” (does that make it a meta-meta-analysis?) carried out by Janet Hyde at the University of Wisconsin-Madison. Less than a quarter of the meta-analyses she looked at showed a significant difference between men and women on the average measures of whatever trait they were examining. This article goes into some of the interesting wrinkles in research into traits such as aggressiveness and verbal ability. Overall this article seemed fairly sensitive to the complexities of research into sex differences in behavior.

Coincidentally, I also ran across this article in the San Francisco Chronicle about a new book by neuropsychiatrist Louann Brizendine, The Female Brain. The book covers studies across a range of disciplines on female/male differences, and also is informed by Brizendine’s work as a clinical psychiatriast working specifically with women and teenaged girls. This sounds like a fascinating read for thinking-meat types, and I’m looking forward to reading it. I think it’s been silly for sex difference research to be judged politically incorrect in some circles, especially among those who fear that it would provide a basis for “biology is destiny” arguments against equal rights for women. It’s obvious to me that there are innate differences between the male and female brain, and I’m very curious, as Brizendine evidently is, about how these differences interact with our social environment to create individual personalities. However, at least judging by what the review says, it sounds almost like the book goes too far in emphasizing the differences (the references to John Gray’s “Men are from Mars, Women are from Venus” books didn’t help any) and assuming that all women are more like each other than in fact I think they really are. I’m uncomfortable with the idea of saying that workplaces should accommodate employees who are mothers because women, according to Brizendine, “are wired to take care of children, and they want that time and need that time.” There are plenty of things that people are wired to want to do, and that in no way obligates anyone else to help them do them. A much more sensible argument, to me, is that raising children is an important part of the necessary work of the world and should be treated with the respect, compensation, and support due to any other form of necessary work. (And furthermore, not all women are equally motivated to take care of children, and plenty of men derive great satisfaction from being parents too. I don’t like the thought of urging employers that all women should be thought of as potential child-bearers who will want to take time away from their jobs to fulfill their need to nurture their children.)

Maybe the book is more nuanced than it appears from the review; I’ll have to read it and find out. But I tend to resist any approach that exaggerates the differences between the sexes and over-emphasizes the similarities between women. To me the most interesting thing is the way that innate biological differences, individual circumstances, and cultural influences shape distinctive personalities and situations. I like to take people on a a case-by-case basis rather than concluding that because they are male or female they automatically possess a certain set of traits. Understanding the average differences in behavior between men and women, and the evolution and biochemistry behind them, is a fascinating pursuit, and knowing that on average men and women will behave differently and want different things is often useful. However, the statistics given at the end of this review give me pause; if they are averages, they are averaged over so broad a range as to be meaningless. The list says they are “neurological differences” but the last one, about women over 50 being more likely to initiate divorce (than whom? younger women, or men over 50, or what?) is simply a statistic about behavior. The first item on the list, though, may be neurological but makes me wonder what on earth it’s based on: “Thoughts about sex enter women’s brains once every couple of days; for men, thoughts about sex occur every minute.” Really, every minute? OK, it’s an average, but if for men the average is every minute, and I suspect there are men for whom “every couple of days” is overstating it, there must be men for whom it’s even more often than every minute, which seems a bit unlikely to me (for one thing, when does it stop being a discrete thought every XX seconds and become a single thought?). And I can tell you for a fact that for this woman’s brain, thoughts about sex visit much more often than every couple of days. It varies depending on a host of factors, but it’s usually far more frequent than that. In general, I would guess that yes, sex often preoccupies most men to a greater degree than it does most women. But for any individual it depends on age, relationship status, health, job pressures, and money worries, to name just a few of the factors involved, and I’m sure there are women who at their least interested still think about sex more often than some men at their most interested. So it strikes me as meaningless to try to quantify the intervals for males and females and expect people to gain some understanding from that.

All this, of course, assumes that the review faithfully reflects the content of the book, and that may not be true. But still, I appreciated the approach of the piece in The Economist much more than I did the tone of this review.

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May 222006
 

Men’s role in the continuation of the human race apparently affects the average length of the male lifespan. This press release describes an investigation into the differing life expectancies of men and women. On average, women live longer than men do, and the difference has been observed in humans as far back as the middle of the 18th century and even appears in chimps and other animals as well as humans. The evolutionary explanation is that the reproductive role of males requires more competitive behavior than the female role. Males are handicapped not only by the physiologically costly or risky behaviors necessary to win mating opportunities, but by the ways the male body has been shaped, down through the generations, by the competition for mates. (This article doesn’t go into details about why, but, for example, male immune systems tend to be more vulnerable.) I’m curious about the data from earlier centuries, because childbirth was for many generations a dangerous enterprise that shortened many women’s lives. I gather that if the average woman could make it through her childbearing years, she had a better chance of making it to advanced old age than the average man.

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