Researchers are finding common biological traits among gay men, suggesting that sexual orientation is an inborn combination of genetic and environmental factors that largely decide a person's sexual attractions.
Richard Lippa, a psychology professor at California State University-Fullerton - compared to straight men, gay men are more likely to be left-handed, to be the younger siblings of older brothers, and to have hair that whorls in a counterclockwise direction.
Lippa claims he found that 21.3 of men at gay pride festivals had counterclockwise hair whorls; under 10% in the general population had clockwise whorls. According to his study, approximately 13% more gay males are left-handed than heterosexual males; 11% of heterosexual males are left-handed. More lesbian woman (13%) are left-handed than straight women; 10% of heterosexual women are left-handed.
Some studies since the mid-1990s have found common biological traits between gay men, including left-handedness and the direction of hair whorls. The likelihood that if one identical twin is gay, the other will be also be gay is much higher than the "concordance" of homosexuality between fraternal twins, indicating that genes play a role in sexual orientation, but are not the entire cause.
Not everyone agrees, Dr. Neil Whitehead, has authored detailed rebuttals to this flawed study and others that purport to show a genetic origin to homosexual behaviors.
Whitehead, writing in "The Importance Of Twin Studies," notes:
Identical twins have identical genes. If homosexuality was a biological condition produced inescapably by the genes (e.g. eye color), then if one identical twin was homosexual, in 100% of the cases his brother would be too. But we know that only about 38% of the time is the identical twin brother homosexual. Genes are responsible for an indirect influence, but on average, they do not force people into homosexuality. This conclusion has been well known in the scientific community for a few decades but has not reached the general public. Indeed, the public increasingly believes the opposite.
There is no evidence of a "gay gene," says Douglas Abbott, Ph.D., Professor of Child and Family Studies at the University of Nebraska.
Abbott points to studies that look at the sexual orientation of the offspring of gay people. "If homosexuality was caused by genetic mechanisms, their children would be more likely to choose same-sex interaction," he says. "But they aren't more likely, so therefore it can't be genetic."
For Abbott, the answer to the nature-vs.-nurture question is very clear. "I think the primary causes of same-sex behavior are environmental and personal choice and free agency," he says. "Can someone change their orientation? The definitive answer to that is, "yes."
Christian groups such as Exodus International argue "that homosexuals who desire to change can do so."
One prominent psychiatrist, Dr Robert Spitzer of Columbia University, found evidence that therapy can cause some gay people to change to a heterosexual orientation, although the study concluded that a "complete change" was uncommon.
Spanish psychiatrist Enrique Rojas says homosexuality is a disorder that can be cured.
The group, Courage Apostolate helps people who suffer from a same sex attraction live chaste lives in accordance with the Roman Catholic Church's teaching on homosexuality.
Researchers are eagerly awaiting a DNA study of male siblings with at least one gay brother by Bailey and other scientists at Northwestern University due in early 2009, because it may shed light on the role genetics plays in sexual attraction. By researching 800 sets of brothers, by far the largest study of its type, the Northwestern study is searching for the specific genes that may influence some brothers to be gay and others to be heterosexual.