Do men and women have different brains?

Scientists have known for a while now that men and women have slightly different brains, but they thought the changes were limited to the hypothalamus, the part of the brain that controls sex drive and food intake. A few scientists may have admitted that men's brains were indeed bigger, but they would have tried to qualify this finding by telling you that it was because men were bigger. Because brain size has been linked with intelligence, it's very tricky to go around saying that men have bigger brains. Yet men do seem to have women beat here; even when accounting for height and weight differences, men have slightly bigger brains. Does this mean they're smarter? Let's keep going.

In 2001, researchers from Harvard found that certain parts of the brain were differently sized in males and females, which may help balance out the overall size difference. The study found that parts of the frontal lobe, responsible for problem-solving and decision-making, and the limbic cortex, responsible for regulating emotions, were larger in women [source: Hoag]. In men, the parietal cortex, which is involved in space perception, and the amygdala, which regulates sexual and social behavior, were larger [source: Hoag].

Men also have approximately 6.5 times more gray matter in the brain than women, but before the heads of all the men out there start to swell, listen to this: Women have about 10 times more white matter than men do [source: Carey]. This difference may account for differences in how men and women think. Men seem to think with their gray matter, which is full of active neurons. Women think with the white matter, which consists more of connections between the neurons. In this way, a woman's brain is a bit more complicated in setup, but those connections may allow a woman's brain to work faster than a man's [source: Hotz].

If you're a lady still concerned about the size issues brought up in the first paragraph, let's address that now. In women's brains, the neurons are packed in tightly, so that they're closer together. This proximity, in conjunction with speedy connections facilitated by the white matter, is another reason why women's brains work faster. Some women even have as many as 12 percent more neurons than men do [source: Hotz]. In studying women's brains, psychologist Sandra Witelson found that those neurons were most densely crowded on certain layers of the cortex, namely the ones responsible for signals coming in and out of the brain. This, Witelson believed, may be one reason why women tend to score higher on tests that involve language and communication, and she came to believe that these differences were present from birth [source: Hotz].

But the density of women's neurons, much like the size of a guy's brain, isn't any sort of magic bullet for predicting intelligence. Scientists know this because they've conducted imaging studies on how men and women think. As we've said, men use gray matter, and women use white, but they're also accessing different sections of the brain for the same task. In one study, men and women were asked to sound out different words. Men relied on just one small area on the left side of the brain to complete the task, while the majority of women used areas in both sides of the brain [source: Kolata]. However, both men and women sounded out the words equally well, indicating that there is more than one way for the brain to arrive at the same result. For example, while women get stuck with a bad reputation for reading maps, it may just be that they orient to landmarks differently. And as for intelligence, average IQ scores are the same for both men and women [source: Crenson].

But do we get to these IQ scores through nature or nurture? On the next page, we'll examine whether these different brain structures are set at birth, or whether they're shaped by the environment.

There may be subtle differences in how even the most equality-minded among us treat baby girls versus baby boys. Girls may be dressed in pink and given dolls, while boys wear blue jumpers and push around trucks. To some people, these environmental factors are impossible to ignore when considering the human brain. If there are differences in people's brains, it might be due to how society has shaped a person, with neurons and synapses pruned away as the brain deemed them unnecessary.

Sandra Witelson, the psychologist mentioned on the previous page, disagrees with that environmental assessment, and she uses an unlikely source to support her belief that our brains are structured at birth: Albert Einstein. Witelson had the opportunity to study pieces of Einstein's brain, and she found its unique structure to be a sort of confirmation that some brain differences simply can't be explained away with social or environmental reasons [source: Hotz]. She didn't look at Einstein's intelligence or accomplishments, but she simply observed that he had a unique brain structure that was likely already formed at birth.

This may help to explain why we don't have many Einsteins running around. And when it comes to the stereotype of women underperforming at Einstein's favored subjects of physics and math, that may just come down to slight differences in the brain as well. It may be that girls' and boys' brains develop at different rates. Our educational system, however, doesn't take that into account. When a child encounters a subject that his or her brain is not ready to tackle yet, the child may become frustrated and give up too quickly [source: Ripley].

To tease this out a bit further, girls may start to discern that boys do better in math classes, and that girls in their peer groups are electing not to take more advanced versions of the subjects. This can cause further drops in female enrollment in math and physics courses: One study showed that female students with math, science and engineering majors were uninterested in attending a summer math and sciences conference after they were shown videos in which the gender ratio was unbalanced, with three males for every one female [source: Bryner].

However, another study demonstrated that this sort of insecurity is all in our heads. In that study, girls' math scores improved when they were told that the exam was gender-neutral, while white men's scores on the same test dropped when they were told the scores would be evaluated against Asian men's scores [source: Crenson]. This seems to suggest that we can easily overcome any biological differences, or we can just as easily doom ourselves to fulfilling these prophecies.

But at this point, instead of wondering whether we need to revamp the educational system or worry about whether a different brain could become grounds for not hiring someone, it may be more important to focus on how knowing about these differences could help us. Most research for new medications is conducted on male volunteers and male animals exclusively, because it was believed that the female brain would show wildly erratic results during various phases of the menstrual cycle [source: Hoag]. Knowing about the differences in male and female brains could open up tremendous opportunity in diagnosing and treating brain disorders.

For example, depression and chronic anxiety are diagnosed far more often in women; this may have to do with differences in the chemical composition of the brain, as one study has shown that women produce only about half as much serotonin (a neurotransmitter linked to depression) as men and have fewer transporters to recycle it [source: Karolinska Institutet]. Or, it may have to do with how the various sides of the female brain respond to emotions and pain. Men, on the other hand, are more likely to be diagnosed with autism, Tourette's syndrome, dyslexia and schizophrenia, to name a few [source: Hoag]. Additionally, disorders like schizophrenia and Alzheimer's disease can show up differently in men and women [source: Society for Women's Health Research]. Based on the location of neurons, brain injuries may affect men and women differently [source: Carey].

This sort of knowledge could affect drug treatments, or at least explain why some drugs work differently in men and women. It extends beyond just drugs, though. One study has found that men and women's brains fire differently when they do plan a visually guided action, like reaching for an object. This may necessitate changes in physical therapy after a brain disorder that affects one side of the brain, like a stroke [source: York University].

Scientists have more work to do in learning about the human brain. If you'd like to learn more about the brain, gender and related topics, visit the links on the next page.