TUESDAY, May 10, 2005 (HealthDayNews) -- The latest research indicating that at least some aspects of homosexuality may be "hard-wired" into the brain has once again fanned the flames of debate.
Swedish scientists claim that chemicals called pheromones that affect our sense of smell are different for gay men and straight men, providing another biologic basis for different sexual orientation. Adding fuel to the fire is the finding that gay men's brain reactions to the chemicals were similar to women's reactions.
All the researchers say is, "These findings show that our brain reacts differently to the two putative pheromones compared with common odors, and suggest a link between sexual orientation and hypothalamic neuronal processes."
Pheromones are chemicals that send sexual messages as often undetectable odors to individuals of the same species. In their study, the researchers found that a pheromone in the perspiration of homosexual men causes a similar reaction in other gay men and heterosexual women.
According to the report in the May 10 issue of the Proceedings of the National Academy of Sciences, the research team looked at compounds that include a testosterone derivative called 4,16-androstadien-3-one (AND), and the estrogen-like steroid estra-1,3-5(10),16-tetraen-3-ol (EST).
The researchers found that AND activated the hypothalamus in homosexual men and heterosexual women, but not heterosexual men. Additionally, EST activated the hypothalamus only in heterosexual men.
"The regions of the brain involved have been found to be involved in sexual behavior, based on animal studies," said Brian Mustanski, from the department of psychiatry at the University of Illinois at Chicago. "Some previous studies also found differences between gay and straight men in these brain regions," he added.
Mustanski noted that this study suggests a link between sexual orientation and brain processes, specifically in the hypothalamus. "Another study, to soon be published in Psychological Science, found differences in the odors of gay and heterosexual men," he said.
Taken together, these studies suggest that sexual orientation has a biological component related to body odor and possible pheromones, Mustanski said. "It also helps to demonstrate that sexual orientation is not a simple choice -- how could such a choice influence the production of and response to body odors?
"These studies converge with previous research using family studies, twin studies, and molecular genetic studies to show that sexual orientation is at least partly determined by biology," he said.
But other experts see it differently.
"This study says nothing about homosexuality being innate," said Dr. Jeffrey Satinover, a psychoanalyst who has written about homosexuality and lectured on its social consequences. "There is an automatic knee-jerk assumption that if there is a difference in the brain, that difference has to be innate," he added.
Changes in the hypothalamus could be caused by repetitive sexual behavior, Satinover said. "The brain is extremely plastic, like a muscle," he said.
"There have been dozens and dozens of studies attempting to show a genetic or biological basis for homosexuality," Satinover said. "Not one has ever succeeded in doing so."
Warren Throckmorton, an associate professor of psychology at Grove City College, a Christian-based college in Pennsylvania, finds the study intriguing. "It does show that there is some involuntary reaction on the part of the brain to a stimulus that is imperceptible to the person," he said.
But like Satinover, Throckmorton believes that the sense of smell is partially learned. "The brains of the participants may have acquired a sexual response to these chemicals as a result of past sexual experiences," he said. "So, learning could be implicated here in a way the subjects wouldn't have been aware of."
From a political perspective, whether homosexuality is innate or learned misses the point, according to Winnie Stachelberg, a vice president at the Human Rights Campaign Foundation, an umbrella organization for gay and bisexual causes. "How we treat people should be based on principles of basic fairness and not on scientific evidence," she said
"This study adds to the scientific evidence around sexual orientation. It points to the need for continued research in this area," Stachelberg added. "In addition, studies like this help people understand each other and alleviate fear."
The Council for Responsible Genetics can tell you more about genes and sexual orientation.