Sex Hormones Determine Male and Female Brain Differences

From Monkeys to Humans, Hormones Shape Brains

A female vervet monkey conducting an anogenital inspection (examining the genital area of the doll in an attempt to determine whether it is male or female), and a male vervet monkey pushing a police car back and forth.
Credit: Gerianne Alexander

Scientifically Correct, but Not Politically Correct

Prenatal exposure to sex hormones shapes the neonatal brain from the very beginning. Testosterone pouring out of the tiny testicles of male fetuses begins to cause the differentiation of the male brain from the female brain starting in the first trimester of pregnancy.

New and ongoing research suggests babies’ exposure to hormones while they are in the womb causes their toy preferences to emerge soon after birth. As for why evolution made this so, questions remain, but the toys may help boys and girls develop the skills they once needed to fulfill their ancient gender roles.

… At just 3 months old, the newborn boys already fixed their eyes on the toys associated with their gender. __

Not only are boys showing preferences for different types of toys from the earliest age. They are also beginning to exhibit superior spatial skills of particular kinds. Young girls, for their part, exhibit superior recall of word lists — a verbal skill.

Although it used to be thought that sex differences in problem solving did not appear until puberty, the accumulated evidence now suggests that some cognitive and skill differences are present much earlier. For example, researchers have found that three- and four- year-old boys were better at targeting and at mentally rotating figures within a clock face than girls of the same age were. Prepubescent girls, however, excelled at recalling lists of words. __

What Happens With Administration of Cross-Sex Hormones?

When female hormones are given to men, and male hormones are given to women, some interesting paradoxical brain effects tend to emerge. Before “cross-sex hormone treatment,” brain size measures between normals and sex-matched “transsexuals” were not different. But after cross-sex hormone total brain volumes changed in an interesting way . . .

The changes in total brain and hypothalamus volumes following cross-sex hormone treatment in the transsexuals were mirrored by changes in their third and lateral ventricle volumes, i.e. treatment with estrogens and anti-androgens in MFs increased third and lateral ventricle volumes, whereas treatment with androgens decreased the third and lateral ventricle volumes in FMs. This suggests that the total brain volume changes are at least in part due to changes in medial brain structures surrounding these ventricles (including, but not limited to, the hypothalamus, which lies in close proximity to the third ventricle). Considering that the effects were not specific for gray (neurons, glia) or white (myelinated axonal fibers) matter suggests that both alterations in nerve cells as well as in axonal fibers may be implicated in the anatomical brain changes following cross-sex hormone treatment in humans. It is not surprising that the influences of sex hormones on the brain were not limited to the hypothalamus, but were also expressed as changes in total brain size. Estrogen and androgen receptor mRNA containing neurons are not limited to the hypothalamus, but are distributed throughout the adult human brain (18). __ Sex Hormones Change the Brain

In other words, giving male hormones to women changes their brains to be more like male brains. Giving female hormones to men shrinks brain volumes to be more in keeping with female brain size.

Mathematical Abilities Vary at the Extremes

Science of Sex Differences in Science and Mathematics
Psychological Science in the Public Interest

There are more males at both ends of the aptitude spectrum, due to a higher variability in cognitive skills. Men and women are roughly equivalent in the mid-ranges of maths, engineering, and math-dependent science aptitudes. But at the upper extremes where the truly advanced work is being done, most of the high-achievers in mathematics, engineering, the hard sciences, economics, and other math-requisite fields, are men.

Men and Women Make Different Career Choices

In addition to the male advantage at higher levels of aptitude in mathematics and spatial rotation, males tend to be more naturally attracted to careers in engineering, hard sciences, and other math-requisite fields.

Sex Differences in Mathematical Abilities

These are important questions to answer before evaluating studies that try to determine whether sex-differences in particular abilities exist. One of the mistakes that sex-denial researchers often make is to ignore those critical questions. This reveals them as either incompetent, dishonest, or ignorant of the normal course of hormone induced brain changes through the developmental cycle.

The Brain Responds to Sex Hormones Throughout Life

Normal levels of testosterone are appreciably higher in men than in women throughout life. Higher is not necessarily better, since men with lower levels of testosterone tend to perform better at mathematical tasks than men with quite high levels of testosterone.

The opposite is true for women, where higher levels of testosterone tend to correspond to superior mathematical skill. In fact, the sweet spot for mathematics may depend upon the “balance” of the sex hormones — androgens vs. estrogens:

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. __

Normal testosterone levels for men: 300 to 1000 ng/dl
Normal testosterone levels for women: 30 to 95 ng/dl

In the video above, sex researcher Dr. Debra Soh speaks out about sex brain differences, and how some corrupt academics and charlatans are trying to shut down honest research and the conversation.

Hormonal Surges Take Place at Different Stages of Life

In the prenatal environment, testosterone output by tiny male testicles has a profound effect on the rapidly developing fetal brain. In the pubertal environment, an even greater surge in testosterone output takes place in males — and a powerful estrogen surge occurs in females.

The undeniable divergence of male-female body morphology at and after puberty can be seen by anyone with eyes or hands. But to see the divergence in the brain between males and females requires a minimal level of intelligence and honesty — both of which are often in short supply in today’s academic, government, and media environments.

This entry was posted in Childhood Development, Cognition, Human Brain, Sex Differences, Testosterone and tagged , . Bookmark the permalink.

1 Response to Sex Hormones Determine Male and Female Brain Differences

  1. JerryO says:

    Outstanding post, as always. I’m so sick of all the Libbies and their “gender choice” BS… it’s mind-numbing how dumb that is…

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