同性戀基因延續之謎 – C. Moskowitz

How Gay Uncles Pass Down Genes

Clara Moskowitz, LiveScience Staff Writer, LiveScience.com 

Maybe everyone could use a gay uncle.

A new study found that homosexual men may be predisposed to nurture their nieces and nephews as a way of helping to ensure their own genes get passed down to the next generation.

Research has confirmed that male homosexuality is at least partly hereditary - it tends to cluster in families, and identical twin brothers of gay men are more likely to be gay than fraternal twin brothers, who do not share identical DNA.

But scientists have been puzzled about how these genes are perpetuated, since homosexual males are less likely to reproduce than straight males. Basically, why haven't gay people gone extinct?

One idea is called the "kin selection hypothesis." Perhaps gay men are biologically predisposed to help raise the offspring of their siblings and other relatives.

"Maybe what's happening is they're helping their kin reproduce more by just being altruistic towards kin," said evolutionary psychologist Paul Vasey of the University of Lethbridge in Canada. "Kin therefore pass on more of the genes which they would share with their homosexual relatives."

Vasey and his student Doug VanderLaan tested this hypothesis among a group of men called fa'afafine on the Pacific island of Samoa. Fa'afafine are effeminate men who are exclusively attracted to men as sexual partners, and are generally recognized and tolerated as a distinct gender category - neither male nor female.

The researchers surveyed about 300 fa'afafine, and found that they were significantly more likely to be altruistic toward their nieces and nephews than either single men or women, or mothers or fathers. The scientists call this behavior avuncular, or uncle-like.

The fa'afafine reported being much more willing to pay medical and school fees for their nieces and nephews, to help them with homework, babysit, teach them songs and dances. And a follow-up study confirmed that fa'afafine had indeed spent more money on their young relatives than straight people.

"I am convinced that the fa'afafine have significantly higher avuncular tendencies than men and women," Vasey told LiveScience. "And [the] latest batch of data seems to indicate that this manifests in [the] real world."

In their most recent study, the researchers tested whether fa'afafine are simply more altruistic toward everyone, or if their attention is targeted at their genetic kin. Only the latter would help explain how homosexual genes are passed down through generations.

"We thought maybe they just like helping kids in general, so we compared their avuncularity to kin and non-relations, and we found a significant difference," Vasey said. "They're interested in helping their nieces and nephews, and not in non-kin children."

This divergence differed from straight men and women, who tended to show a more equivalent level of altruism to related and non-related children. This implies that the behavior is an evolutionary adaptation, the researchers say.

"If fa'afafine have really been selected to be avuncular and this is an adaptation, then they would not be redirecting resources to non-kin children," Vasey said.

The researchers published their findings in a February issue of the journal Psychological Science.

The kin selection hypothesis was first proposed in the 1970s, but previous efforts to test it among gay male populations in Western societies found no effect. A study in Chicago and another in England found no difference between gay men and straight people in altruistic behavior toward family members.

"I thought, 'Well, I'll do the study in Samoa, it's a non-Western culture and I'll get the exact same results and it'll be the nail in the coffin for this theory,'" Vasey recalled. "We analyzed the data and we found a significant result for avuncularity. I couldn't believe it. I told them go back and check the data - we must have made a mistake."

But subsequent attempts to reproduce the results confirmed the findings in Samoa.

Vasey said he suspects that the conditions just aren't right in modern Western societies for this genetic predisposition to express itself.

One major cultural difference is the individualistic nature of Western society, compared with the collectivistic culture in Samoa.

"We think we're close to our families, but Samoans are really close to their families," Vasey said. "People are more geographically connected in Samoa."

Additionally, there is less discrimination against fa'afafine, compared with the still-widespread homophobia that exists in many Western societies. Even if many Western gay men wanted to be doting uncles, their families might not always encourage it.

Vasey said the next step is to test whether this trend exists in other non-Western cultures where males with same-sex attractions are also accepted as a unique category.

He also said that he doesn't think the kin selection hypothesis entirely accounts for the endurance of gay genes, but that it likely plays a role in combination with other biological factors.

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