Paul Vasey is one of the luckiest sexuality researchers working today.

Not only has he secured funding for basic sexuality research — a low priority for most research institutions — but he also gets to do his work on the tropical islands of Samoa.

“Samoa has become a second home to me,” said Vasey, who teaches at the University of Lethbridge in Alberta, Canada. Since 2003, he has spent up to a third of every year on the remote archipelago in the central South Pacific. It’s there he hopes to understand the evolutionary basis for what would appear to be a genetic dead end — same-sex attraction.

With little acknowledged evidence for the existence of homosexuality in nature, and no sound theories to explain its evolutionary purpose, much of society and science have long viewed same-sex attraction as abnormal and deviant. Only in 1973 did the American Psychiatric Association remove homosexuality from its list of mental disorders.

Today, we know homosexual behavior occurs in many animals — from beetles to birds to bison — as well as in humans, but scientists still question how such behavior could have arisen naturally.

Vasey believes Samoa may hold a possible answer. He has found evidence on the tropical islands he frequents to support a hypothesis that same-sex attraction confers an evolutionary advantage to humans by increasing a family’s reproductive rates, as well as ensuring the well-being of future generations.

Studies on families with gay members have repeatedly suggested homosexuality has a genetic component. However, biologists struggle to explain how genes contributing to homosexuality could have stuck around in human evolution. Normally, traits that reduce an individual’s reproductive success, which same-sex attraction would appear to do, would not be maintained in the gene pool.

The kin selection hypothesis, introduced in the 1970s, proposed a possible advantage homosexuality would have for humans. The hypothesis says that while homosexual individuals do not directly pass on their genes to successive generations by having children, they indirectly spread their genes through their families.

By devoting their energy to raise their nieces and nephews instead of having children of their own, homosexuals would allow their siblings to have more children and ensure that these offspring live to have children of their own. Thus, homosexual individuals would promote greater reproductive and survival rates of the relatives who share many identical genes with them — including those that may contribute to homosexuality — guaranteeing these genes are passed on to future family members.

Though seemingly logical to many researchers, the idea lost credibility as European and North American studies failed to find evidence that gays devote a significant amount of time and energy to caring for their siblings’ children. Vasey decided to test the hypothesis somewhere else. To eliminate influences Western culture may have had on previous studies, Vasey studies the faʻafafine, feminine Samoan males who reject the labels of “gay” and “homosexual” but acknowledge their primary sexual attraction to adult men.

Vasey is also interested in the Samoans because their social environment closely resembles the one in which our ancestors evolved. “Individuals in the family are interconnected in ways that don’t characterize European society anymore,” Vasey said. “Samoans remain close to their family in ways that characterize the evolutionary past.” Also, Samoan society fully accepts the faʻafafine, who Vasey said are considered to occupy a third gender and are respected for their commitment to taking care of their families.

Vasey analyzed how Samoan men, women and faʻafafine acted toward their nieces, nephews and unrelated children living in the same village, looking at behavior and attitudes such as their willingness to babysit and contribute financial resources. In results to be published in the February 2010 issue of Psychological Science, Vasey found the faʻafafine were more willing to help their nieces and nephews and less likely to help other children compared to their straight counterparts, even when controlling for age, income levels and number of biological children.

Though not conclusive, these results fall in line with the kin selection hypothesis. “You would expect there to be selection to make faʻafafine as efficient as possible in terms of channeling resources and energy toward nieces and nephews without having resources and energy diverted toward non-kin,” Vasey said.

Cognitive biologist Qazi Rahman from the Queen Mary, University of London believes Vasey’s work has revitalized the kin selection hypothesis. “I didn’t think it had any use anymore,” he said. “But now the science is different.”

Nevertheless, some experts caution against jumping to conclusions based on Vasey’s results. “While his science is strong, a lot more has to be done to convince me,” said Northwestern University psychologist Michael Bailey, who found no evidence supporting kin selection in a 2001 study with American homosexual males. “The math still isn’t there.”

Also, while this work might explain the prevalence of gay men, evidence of evolutionary pathways for female homosexuality has proven elusive, as female sexuality seems “more fluid,” and harder to categorize than male sexuality, according to Vasey.

Next year, Vasey plans to further test the kin selection hypothesis by studying faʻafafine avuncularity, or uncle-like behavior, and its measurable effects on children. He also plans to investigate whether Samoans “just expect faʻafafine to behave in a more avuncular manner.” However, Vasey stresses that a cultural expectation does not “invalidate the evolutionary mechanism,” as biological and cultural influences most likely work in concert.

Vasey, who is gay, understands that some may use his sexuality to discount his results. Nevertheless, he stands by his work.

“We’ve just found over and over again consistent evidence in support of these evolutionary pathways,” Vasey said. “When I first started, I thought we’d do one study on this, the results would be negative, and that would be the end of it. No one is more surprised by the results than me.”

*Correction (January 11, 2010): This sentence originally read: “Only since 1973 has the American Psychological Association removed homosexuality from its list of mental disorders.”

**Correction (January 13, 2010): This sentence originally read: “By providing support to raise their nieces and nephews instead of having children of their own, homosexuals would allow their siblings to have more children and ensure that these offspring live to have children of their own.”