A recent ABC article, prompted by Harvard's President Summer's controversial remarks, overviews research that establishes biologically-based differences between the sexes. Such differences may not be deterministic in terms of human character, intelligence, or other potentials, but they are suggestive and merit further investigation.

For example, when it comes to disease:

"Depression, for example, appears to be twice as common in women as in men while women with schizophrenia seem to suffer less cognitive difficulties than men with the condition.

Nearly all neurodevelopmental diseases are either more common in one gender or more severe among one gender, says Nancy Forger of the University of Massachusetts at Amherst. Other conditions, including arthritis, heart disease, even lung cancer also seem to be influenced by a person's gender."

Also, when it comes to brain damage and memory encoding / structural functionality:

"Studies in people with damage to the left sides of their brains, for example, show that men with damage are less likely to be able to recover their ability to talk. The work, from researchers in Bonn, Germany, suggested that men's verbal abilities may stem mostly from the left side of the brain. Meanwhile, women with left brain damage usually retained some language skills.

This difference might partly explain why studies have shown that infant girls speak sooner and use more words than infant boys.

Other work has tapped functional MRIs — scanning devices that measure blood flow and activity in the brains of conscious subjects. Drs. Ruben and Raquel Gur at the University of Pennsylvania have shown that women's brains light up in more areas than men's brains when given verbal and spatial tasks. This feature, they argue, may enhance women's ability to focus on many tasks at once. Women may even use different pathways than men when thinking and encoding memories.

Turhan Canli, a Stanford psychologist, recently tested 12 men and 12 women in functional MRIs and showed that women encode memories using different pathways than what men use when recording memories. The women were later able to recall emotions of a memory more accurately than men, which could possibly stem from how their memories were encoded in the first place.

Other differences keep emerging, including variability in size of the different brain regions, including the hippocampus, the amygdala and certain brain cell clusters." Researcher Nancy Forger of UM-Amherst reports over 100 differences between male and female brains have been discovered so far. For instance:

"Forger's work in mice has shown that as mammals develop in the womb, testosterone and related hormones trigger cell death in some regions of the male brain and foster cell development in other regions. In this way, the hormone sculpts the male brain and how it will differ from the female version.

Remove or add testosterone to mice shortly after birth, and their brains develop according to the presence of the hormone, regardless of their sex."

The article's last point, about the impact of sex-associated hormones on brain development and activity seems to be, from my other reading on the subject, the hottest area of current research. An article at Scientific American takes this research and applies it to activity performance differences by men and women.

The performance differences, again, are more suggestive than conclusive when it comes to educational or career preditors. Research shows that men "tend to perform better than women on certain spatial tasks," especially three-dimensional ones. Women, however, perform better on tasks that involve perceptual speed, such as when matching items (objects with two-dimensional shapes). Women also tend to demonstrate better ability at textual recall, manual dexterity, and mathematical calculations. Men, however, show greater ability at mathematical reasoning, target-directed motor skills, and matching lines with identical slopes.

One interesting claim in this article is that sex-differences in these areas of ability are now found to appear before puberty, not at or after puberty as was often previously claimed.

The main controversy on which the article touches is the question of whether women's tendency to perform less ably in mathematical competition is the result of biology or socialization:

"...Such findings are relevant to the suggestion by Camilla P. Benbow, now at Vanderbilt University, that high mathematical ability has a significant biological determinant. Benbow and her colleagues have reported consistent sex differences in mathematical reasoning ability that favor males. In mathematically talented youth, the differences were especially sharp at the upper end of the distribution, where males vastly outnumbered females. The same has been found for the Putnam competition, a very demanding mathematics examination. Benbow argues that these differences are not readily explained by socialization."

However, the writer cautions, "It is important to keep in mind that the relation between natural hormone levels and problem solving is based on correlational data. Although some form of connection between the two measures exists, we do not necessarily know how the association is determined, nor do we know what its causal basis is. We also know little at present about the relation between adult levels of hormones and those in early life, when abilities appear to become organized in the nervous system."

Another interesting finding the article notes is that both men and women may be affected by fluctuating / cycling hormonal levels:

"One of the most intriguing findings in adults is that cognitive patterns may remain sensitive to hormonal fluctuations throughout life. Elizabeth Hampson of the University of Western Ontario showed that women's performances at certain tasks changed throughout the menstrual cycle as levels of estrogen varied. High levels of the hormone were associated not only with relatively depressed spatial ability but also with enhanced speech and manual skill tasks. In addition, I have observed seasonal fluctuations in spatial ability in men: their performance is better in the spring, when testosterone levels are lower. Whether these hormonally linked fluctuations in intellectual ability represent useful evolutionary adaptations or merely the highs and lows of an average test level remains to be seen through further research."

PMS, indeed :).