Editor’s Note: This article is the first in a series of columns about men and women.

Last weekend, I had the privilege of spending an evening with, among others, a three-year-old girl and her one-year-old brother. Their parents remarked and my observation affirmed that the children were incredibly different — more stereotypically male and female than they or I expected. I might have dismissed their observations as stereotypes, if the girl and her brother (let’s call them Anne and John) didn’t remind me so much of what I’ve seen of myself and my brother in family videos.

Anne and I were both voluble and volatile — quick to cry, enamored of clothing, sensitive, easily scared and constantly whining. John and my brother rarely made a sound, were mostly calm and would have been very easy babies if only they weren’t so mobile and prone to manipulating things (e.g. John turned the fax machine on and off several dozen times, came close to knocking over everyone’s beer can and opened the dishwasher, pulling out hefty vegetable knives).

Seeing these children reminded me that, as politically incorrect as it is to say so, male and female minds are fundamentally different. Certainly, social expectations have some affect on people’s interests and expectations for themselves. However, I had to wonder whether a girl who was barely old enough to communicate with adults could be picking up her love of dresses and chatter from them, or whether a boy too young to talk could be getting the idea from adults that such behavior wasn’t expected of him.

Indeed, children show marked gender differences in their behavior far before they could reasonably be interpreting different societal expectations.

Early in life

• At one day old, boys look at mobiles longer than newborn girls.

• At 12 months, girls look at human faces longer. Researchers at Cambridge found that girls look at faces longer than boys.

• The same Cambridge team found that one-year-old boys preferred watching a film showing cars to one showing a person. Girls showed the opposite preference.

• At a few hours, old girls are more sensitive than boys to touch. Tests between the sexes of tactile sensitivity in the hands and fingers produce differences so striking that sometimes male and female scores do not even overlap, with the most sensitive boy feeling less than the least sensitive girl.

• When it comes to sound, infant females are much less tolerant — one researcher believes that they may “hear” noises as being twice as loud as do males. Baby girls become irritated and anxious about noise, pain or discomfort more readily than do baby boys.

• According to Anne Moir and David Jessel in “Brain Sex: The Real Difference Between Men and Women,” “[a]t four months, most baby girls can distinguish photographs of people they know from photographs of strangers; baby boys cannot.”

• Researchers found three- and four-year-old boys to be better at mentally rotating figures than girls of the same age. — ibid.

• Doreen Kimura, the co-author of the 1994 paper, “Cognitive Pattern in Men and Women Is Influenced by Fluctuations in Sex Hormones,” “[f]or the past few decades, it has been ideologically fashionable to insist that these behavioral differences are minimal and are the consequence of variations in experience during development before and after adolescence. Evidence accumulated more recently, however, suggests that the effects of sex hormones on brain organization occur so early in life that from the start the environment is acting on differently wired brains in boys and girls.”

Different aptitudes?

• Boys outnumber girls four to one in remedial reading classes, according to the book “Brain Sex.”

• “When asked to judge when someone might have said something potentially hurtful, girls score higher from at least seven years old. Women are also more sensitive to facial expressions. They are better at decoding non-verbal communication, picking up subtle nuances from tone of voice or facial expression or judging a person’s character,” writes Simon Baron-Cohen in an article in The Guardian. He writes further that men tend to show “direct” aggression such as hitting whereas women show covert or relational aggression, such as gossip or verbal insults. His thesis in the book, “The Essential Difference: The Truth about the Male and Female Brain,” is that women’s brains are designed for empathy whereas men’s are built for understanding and building systems.

• The amygdala, the brain’s emotion-control center, shows significantly higher levels of activity in males viewing sexual visual stimuli than females viewing the same images, according to a study led by Emory University psychologists Stephan Hamann and Kim Wallen.

• Women might have better short-term memories. They can store greater amounts of irrelevant and random information than men, who seem to need the information to be organized in order to remember it.

• Doreen Kimura writes in “Sex Differences in the Brain” that “[m]en tend to perform better than women on certain spatial tasks. They do well on tests that involve mentally rotating an object or manipulating it in some fashion, such as imagining turning [a] three-dimensional object or determining where the holes punched in a folded piece of paper will fall when the paper is unfolded. Men also are more accurate than women at target-directed motor skills, such as guiding or intercepting projectiles. They do better at matching lines with identical slopes. And men tend to do better than women on tests of mathematical reasoning.”

• On the other hand, “Women tend to perform better than men on tests of perceptual speed in which subjects must rapidly identify matching items ... When reading a story, paragraph or a list of unrelated words, women demonstrate better recall. Women do better on precision manual tasks — that is, those involving fine motor coordination — such as placing the pegs in holes on a board. And women do better than men on mathematical calculation tests.”

• Vanderbilt researchers find that among a sample of 40,000 “gifted” 12- to 14-year-olds who took the SAT, about twice as many boys as girls scored above 500 on the math section; four times as many scored above 600; and 13 times as many boys than girls scored above 700. Boys and girls performed approximately the same on the verbal portion.

• UCLA researchers performed brain scans on people who scored in the 99th percentile on the math portion of the SAT and found that as they worked on problems, the men relied on grey matter in the cerebral and parietal cortices, whereas women showed more activity in areas with white matter, sparking the observation by Richard Haier, a professor of psychology at the UCLA Medical School that “Maybe [the women] are doing the math using the white matter.”

Structural differences

• Haier and his colleagues at the University of New Mexico and the UCI Brain Imaging Center found that men have about six-and-a-half times the amount of gray matter related to general intelligence than women, and women have nearly 10 times the amount of white matter related to intelligence than men. “These findings suggest that human evolution has created two different types of brains designed for equally intelligent behavior,” Haier said. Gray matter is used for information processing, while white matter consists of the connections between processing centers.

• Rex Jung, a co-author of the study, suggested that this difference in white and gray matter between the sexes might help to explain why men excel at local processing tasks while women tend to be good at integrating and assimilating information from distributed gray-matter regions.

• In this same study it was found that 84 percent of gray-matter regions and 86 percent of white-matter regions involved with intellectual performance in women were found in the brain’s frontal lobes, compared to 45 percent and zero percent for males. Thus, most of women’s brain matter involved in intelligence is in the frontal lobes, whereas the grey and white matter involved in men’s intelligence is distributed throughout brain regions. The researchers remarked that this finding that women’s intelligence processing is concentrated in the frontal lobe is consistent with findings that frontal brain injuries can hurt women’s cognitive performance more than men’s.

• A similar study at McMaster University found that women have up to 15 percent more brain-cell density in certain areas of the frontal lobe, which controls so-called higher mental processes including judgment, personality, planning and working memory.

• Parts of the corpus callosum, a major neural system connecting the two hemispheres, as well as the anterior commissure, another connecting structure, are larger in women, which might enable better communication between hemispheres.

• Men seem to have greater asymmetry between brain hemispheres, and damage to one hemisphere often has more of an effect on cognition than a similar injury in women.

Hormones affect the brain

• Canadian researchers found prenatal testosterone levels were positively correlated with skills on a mental rotation test (imagining objects being rotated).

• Males with IHH (idiopathic hypogonadotrophic hypogonadism) have small testes (and therefore low levels of testosterone) and are worse at spatial reasoning.

• Male babies with androgen insensitivity (AI) syndrome are also worse at spatial reasoning.

• Females with CAH (congenital adrenal hyperplasia) have high levels of androgens and enhanced spatial systemizing.

• Researcher Elizabeth Hampson of the University of Western Ontario found that women’s performance on certain mental tasks varied throughout their menstrual cycles. High levels of estrogen were correlated with decreased spatial ability but increased speech and manual skills.

In the day or two that I’ve been looking things up for this column, I’ve been astounded not only at the number of differences between male and female brains, but also at the lack of scientific arguments that the brains are essentially equal. Certainly, people have written that men and women have equal ability, etc. during the Larry Summers ordeal, but among people who study the brain, the consensus seems to be that while intelligence (however it is defined) might be equal, the male and female brains are altogether different animals.

As Moir and Jessel write in “Brain Sex,” “Men are different from women. They are equal only in their common membership of the same species, humankind. To maintain that they are the same in aptitude, skill or behavior is to build a society based on a biological and scientific lie.

We might condone that lie if it helps women to believe that they can perform in technical subjects just as well as men or if it encourages the homogeneity and androgyny our society seems to desire. But there can be huge costs to assuming that besides sexual responses and the like, male and female brains are the same.

I’ll address these consequences in a later column in this series.

Given that Andrea is prefers talking to writing in solitude and also loves Moonbeams’ tea, she’d love to talk with you over hot beverages about sex differences. E-mail her at arunyan@stanford.edu.