When domestic rams eschew female sheep, and instead hang around in the corner of the field with other rams, rubbing each other up, necking and even mounting each other, what is going on? Lord Alfred Douglas, Oscar Wilde’s lover, coined the phrase “The love that dare not speak its name,” in his poem “Two Loves,” which was published in 1894. But what are the rams up to? Is this the love that dare not “baa” its name?
According to researchers at Oregon Health & Science University, it is. Six percent to 8 percent of domestic rams exclusively mate with other rams. The rams have “same-sex preferences,” say the researchers. These sheep, the rest of us would say, are queer. Homosexual behavior has been documented in more than 450 species of animals, including penguins, Japanese macaques, chaffinches, grizzly bears, fruit bats and fruit flies. But what the OHSU scientists, in collaboration with researchers at the U.S. Sheep Experiment Station in Dubois, Idaho, have shown is that the brains of gay and straight rams are different.
More precisely, they have demonstrated that there are structural brain differences associated with naturally occurring variations in sexual partner preferences in sheep.
The results confirm and expand upon human studies that found morphological brain differences between heterosexual men, and homosexual men and women. In 1991, Simon LeVay, a British-born San Francisco-based neuroscientist, published a paper in the journal Science that purported to show a difference in the brains of homosexual and heterosexual men. Another study published the following year showed that part of the brain, the anterior commissure, was twice as large in gay men as in straight men.
But, perhaps due to the long-standing reluctance of biologists to address the question of same-sex preferences outside of humans, no one had looked at brain differences in animals. The paper OHSU biologists presented Monday at the annual meeting of the Society for Neuroscience in Orlando, Fla., is the first time that scientists have examined the brains of domestic animals with respect to sexual orientation.
Sheep selected for this research were chosen after their sexual partner preference and mating habits had been studied for two years. A total of 27 sheep were chosen: nine rams that preferred to mate with males; eight rams that preferred to mate with females; and 11 ewes (it is not clear whether there is such a thing as a lesbian ewe). When researchers compared brains among the three groups, they found marked differences.
The biologists were particularly interested in the preoptic hypothalamus, a region of the brain known to be involved in sexual behaviors and partner preferences. Researchers identified a group of neurons there called the sexually dimorphic nucleus.
“Interestingly, this bundle of neurons is smaller in ewes and in rams with same-sex preferences than it is in rams that prefer ewes,” said Kay Larkin, a postdoctoral fellow in physiology and pharmacology in the OHSU School of Medicine, and lead author of the paper.
“We also determined that the volume of the sexually dimorphic area is approximately the same in rams that prefer rams as it is in ewes.”
The sexually dimorphic nucleus was measured by examining the extent and level of expression of aromatase, a key enzyme in a hormonal pathway that is involved in the development and maintenance of masculine characteristics. Additional groups of neurons within the hypothalamus thought to be involved in other aspects of sexual behavior were analyzed for size differences. These groups of neurons were found to be different in rams and ewes, but not different in the two groups of rams.
The goal of these studies is to improve our understanding of the biological basis of sexual behaviors. More specifically, researchers are trying to determine the role of brain anatomy and physiology in the expression and development of sexual behaviors and traits.
The results of this field of research could have enormous consequences. In 1996, Simon LeVay published “Queer Science.” In it, he wrote: “Most gay men and lesbian women have their own opinions about why they are homosexual. Although there are exceptions, gay men in the United States today generally tend to claim that they were ‘born gay.’ Ninety percent of gay men surveyed by the Advocate magazine in 1994 claimed to have been born gay, and only 4 percent believed that choice came into the equation at all.”
Despite what homosexual men and women might feel, the scientific basis for a claim to be “born gay” is far from conclusive.
LeVay’s 1991 paper in Science was criticized on several counts: no one could check the sexual orientation of the subjects, because they were all dead; moreover, some of the heterosexual subjects had died of AIDS, adding another variable to the mix. Research using animal models like sheep avoids such problems.
The researchers believe the sheep model may also help provide answers about other brain-linked sexual functions. “Future studies will address functional aspects of the observed differences in the hypothalamus and test the hypothesis that differences in brain anatomy and sexual-partner preference arise as a consequence of hormone exposure during fetal development,” said Charles Roselli, professor of physiology and pharmacology in the OHSU School of Medicine, and senior author of the paper. “While we realize that sexuality is more complex in humans than reproductive behaviors in sheep, this model will help illuminate the basic principles that apply to all mammals, and may be helpful in understanding the biology of human behaviors as well.”
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