Low Uterine Testosterone Levels Determine Homosexual Behavior in Males

Finding based on experiments made on orientation ability

What's inside a woman's head is very different from what's inside a man's head.

Researchers know that the way neurons fire inside the brain differs related to sex, and this determines differences in how a woman's and a man's brains function.

Now a research team has found that the way a brain functions, whether womanish or mannish, depends on the womb exposure to sex hormones, a discovery that could explain differences in neuropsychological disorders in men and women, like attention deficit hyperactivity disorder, Alzheimer's disease and autism, and also a cause for homosexuality.

The researchers at the Yerkes National Primate Research Center have used a behavioral trait typical to all female primates, including women: they tend to use landmarks for navigation. "Men, when finding a location, generally use north and south as well as distance estimates whereas women prefer physical cues such as street names, signs and buildings," said lead researcher Dr. Rebecca Herman. "The very fact females and males use different strategies suggests there are subtle sex differences in the way the brain develops."

This is not just a difference in how females and males cope with spatial problems; the difference also stands in which cues they employ in solving problems.

The team compared normal female and male rhesus macaques exposed to different prenatal testosterone levels to see if sex differences were due to "in utero" differences in hormone exposure. A group of females and males received a chemical blocking the testosterone activity while another mixed group received increased testosterone. "There are a number of developmental disorders associated with abnormal levels of hormones. Through a better understanding of how the human brain develops and functions differently in women and men, researchers may be able to develop better treatments for these disorders," said Herman.

The team investigated the individuals when they reached maturity, focusing on how the monkeys navigated into an open area to detect highly valued food items in goal boxes.

The investigators changed the food locations (spatial information) and the number of colored markers (landmarks) on baited goal boxes so they could check the monkeys' memory and use of visual markers. "When both spatial and marker cues were available, performance did not differ by sex or prenatal treatment," said Herman. "When salient landmarks directly indicate correct locations but spatial information is unreliable, females perform better than males," she continued.

"Male subjects whose testosterone exposure had been blocked early in gestation were more able to use the landmarks to navigate than were control males. They performed more like females. This suggests that prenatal testosterone likely plays a role in establishing the sex difference in using landmarks for navigation," said Herman.

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