- The Washington Times - Monday, May 9, 2005


The brains of homosexual men respond more like those of women when reacting to a chemical derived from the male sex hormone, according to new evidence of physical differences related to sexual orientation.

The finding, published in today’s issue of Proceedings of the National Academy of Sciences, shows differences in physiological reaction to sex hormones.

Researchers led by Ivanka Savic at the Karolinska Institute in Stockholm exposed heterosexual men and women and homosexual men to chemicals derived from male and female sex hormones. These chemicals are thought to be pheromones, molecules known to trigger responses such as defense and sex in many animals.

Whether humans respond to pheromones has been the subject of debate, although in 2000 American researchers reported finding a gene that they think directs the human pheromone receptor in the nose.

In the Swedish study, when sniffing a chemical from testosterone, the male hormone, portions of the brains involved in sexual activity were activated in homosexual men and heterosexual women, but not in heterosexual men, the researchers found.

When they sniffed smells such as cedar or lavender, all of the subjects’ brains reacted only in the olfactory regions that handle smells.

The result clearly shows a biological involvement in sexual orientation, said Sandra Witelson, a researcher on brain anatomy and sexual orientation at the Michael G. DeGroote School of Medicine at McMaster University in Ontario.

The research was funded by the Swedish Medical Research Council, the Karolinska Institute and the Magnus Bergvall Foundation.

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