It's a question which has troubled science since Darwin: if homosexuality is, at least in part, inherited, how are those genes being passed down to new generations?
Canadian researchers say they have found the first evidence to back up the theory that gay men have the evolutionary advantage of being "super uncles", a way of enhancing the survival prospects of close relatives and -- indirectly, at least -- making it more likely their genes are passed on.
Paul Vasey, associate professor in the University of Lethbridge's department of psychology, said his research found evidence that gay men may be more willing to support their nieces and nephews financially and emotionally.
The idea is that homosexuals are helping their close relatives reproduce more successfully and at a higher rate by being helpful: babysitting more, tutoring their nieces and nephews in art and music, and helping out financially with things like medical care and education.
The question of whether homosexuality clashes with evolution has puzzled scientists for decades. The trait appears to be inheritable -- but because homosexual men are much less likely to produce offspring than heterosexual men, researchers have struggled to explain why the genes for the trait weren't extinguished long ago.
"Maybe it's in this way that they're indirectly passing on at least some of the genes that they're sharing with their kin," he said.
Researchers conducting similar studies in the U.S. and England did not find any supporting evidence for the theory, said Mr. Vasey. "So I thought, ‘Well, I'll do it in a non-Western culture and chances are I'm going to find exactly the same results and it'll be the nail in the coffin for this hypothesis,'" he said.
Mr. Vasey and University of Lethbridge evolutionary psychologist Doug VanderLaan spent time on the Pacific island of Samoa surveying women, straight men and the fa'afafine -- men who prefer other men as sexual partners and are accepted within the culture as a distinct third gender category. "Some are so feminine that they pass as women to the naive observer," he said.
Mr. Vasey found that the fa'afafine said they were significantly more willing to help kin, yet much less interested in helping children who aren't family -- providing the first evidence to support the "kin selection hypothesis."
"We argue that this would allow the fa'afafine to distribute altruism toward their nieces and nephews in a more efficient and adaptive manner compared to men and women," he said.
The findings are published online this week in the journal Psychological Science.
Researchers are now trying to establish whether the fa'afafine's professed willingness to help their kin is reflected in their actions by studying whether they give more money to their relatives. "It's a crude measure, but it's a start," he admitted.
"There is this distinction between willingness to do something and then do they actually do it in the real world," he added. "Research takes time, so we don't have all the answers right away."
Mr. Vasey said he was initially shocked by the results, and conducted the questionnaire three times to be certain of the results. "I think I've convinced myself it's real," he said.
Mr. Vasey has a few theories about why researchers conducting similar studies in the U.S. and in England found no difference between the way gay men and straight men treat their nieces and nephews. In Samoa, communities are closer geographically and families are more tightly-knit, while North American families are more dispersed, he said. Homosexuality is expressed differently in Western culture -- where it's also less accepted, he said.