Nature vs Nurture

[Shortie (imported)]

I don't know that this research report will settle the question about sexual preferences being due to nature or nurture, but it should help.

BIOLOGY BEHIND HOMOSEXUALITY IN SHEEP, STUDY CONFIRMS

OHSU researchers show brain anatomy, hormone production may be cause

May 5, 2004

PORTLAND, Ore. - Researchers in the Oregon Health & Science University School of Medicine have confirmed that a male sheep's preference for same-sex partners has biological underpinnings.

A study published in the February issue of the journal Endocrinology demonstrates that not only are certain groups of cells different between genders in a part of the sheep brain controlling sexual behavior, but brain anatomy and hormone production may determine whether adult rams prefer other rams over ewes.

"This particular study, along with others, strongly suggests that sexual preference is biologically determined in animals, and possibly in humans," said the study's lead author, Charles E. Roselli, Ph.D., professor of physiology and pharmacology in the OHSU School of Medicine. "The hope is that the study of these brain differences will provide clues to the processes involved in the development of heterosexual, as well as homosexual behavior."

The results lend credence to previous studies in humans that described anatomical differences between the brains of heterosexual men and homosexual men, as well as sexually unique versions of the same cluster of brain cells in males and females.

"Same-sex attraction is widespread across many different species." said Roselli, whose laboratory collaborated with the Department of Animal Sciences at Oregon State University and the USDA Agricultural Research Service's U.S. Sheep Experiment Station in Dubois, Idaho.

Kay Larkin, Ph.D., an OHSU electron microscopist who performed laboratory analysis for the study, said scientists now have a marker that points to whether a ram may prefer other rams over ewes.

"There's a difference in the brain that is correlated with sexual partner preference rather than gender of the animal you're looking at," she said.

About 8 percent of domestic rams display preferences for other males as sexual partners. Scientists don't believe it's related to dominance or flock hierarchy; rather their typical motor pattern for intercourse is merely directed at rams instead of ewes.

"They're one of the few species that have been systematically studied, so we're able to do very careful and controlled experiments on sheep," Roselli said. "We used rams that had consistently shown exclusive sexual preference for other rams when they were given a choice between rams and ewes."

The study examined 27 adult, 4-year-old sheep of mixed Western breeds reared at the U.S. Sheep Experiment Station. They included eight male sheep exhibiting a female mate preference - female-oriented rams - nine male-oriented rams and 10 ewes.

OHSU researchers discovered an irregularly shaped, densely packed cluster of nerve cells in the hypothalamus of the sheep brain, which they named the ovine sexually dimorphic nucleus or oSDN because it is a different size in rams than in ewes. The hypothalamus is the part of the brain that regulates sex hormone secretion, blood pressure, body temperature, water balance, and food intake, while it also plays a role in regulating complex behaviors, such as sexual behavior.

The oSDN in rams that preferred females was "significantly" larger and contained more neurons than in male-oriented rams and ewes. In addition, the oSDN of the female-oriented rams expressed higher levels of aromatase, a substance that converts testosterone to estradiol so that the androgen hormone can facilitate typical male sexual behaviors. Aromatase expression was no different between male-oriented rams and ewes.

The study was the first to demonstrate an association between natural variations in sexual partner preferences and brain structure in nonhuman animals.

The Endocrinology study is part of a five-year, OHSU-led effort funded through 2008 by the National Center for Research Resources, a component of the National Institutes of Health. Scientists will work to further characterize the rams' behavior and study when during development these differences arise. "We do have some evidence that the nucleus is sexually dimorphic in late gestation," Roselli said.

They would also like to know whether sexual preferences can be altered by manipulating the prenatal hormone environment, for instance by using drugs to prevent the actions of androgen in the fetal sheep brain.

In collaboration with geneticists at UCLA, Roselli has begun to study possible differences in gene expression between brains of male-oriented and female-oriented rams.

http://www.ohsu.edu/news/2004/030504sheep.html

[transgirl23ny (imported)]

They would also like to know whether sexual preferences can be altered by manipulating the prenatal hormone environment, for instance by using drugs to prevent the actions of androgen in the fetal sheep

No, thats no good... next thing ya know, the "Christians" will be looking for anti-homosexual pills to administer to pregnant women. I like having a variety of people!!!! Besides, if there were no gay guys... my hair wouldnt come out as good. LOL!!!

[JesusA (imported)]

An earlier report on this project was posted on the Archive in November, 2002. You may want to check out that thread,

Research on homosexuality (http://www.eunuch.org/vbulletin/showthread.php?t=2039).

[philorchites (imported)]

Thanks for posting this in full this time. As I said before, it is kinda neat to think of myself as a ram who prefers other rams. And yes, it goes a long way to addressing the nature/nurture thing.

On that line, the two sides often talk past each other. It is one thing to have an inborn tendency or orientation, and that's the nature part. How one expresses it, and the extent to which one expresses, is all a matter of nuture. Especially how one feels about it! We are only beginning to see a generation of gay men who are allowed to feel OK about being gay, that is, who experience postive or affirming nurture, as opposed to the culture of fear and repression that has prevailed for so long. I suspect they will handle their gayness differently from the way followed by others in the past.