Gay flies 'suggest evolution bonus'
A study of gay fruit flies suggests that being homosexual might carry an evolutionary advantage.
The research points to the possible existence of inherited "gay genes" on the male Y chromosome.
They have been conserved in animals - including humans - because they are linked to fitness traits that help survival, scientists believe.
Without any benefit, genes that cause a species to avoid reproducing would have been weeded out by natural selection.
The study involved screening fruit flies (Drosophla melanogaster) for male-to-male courtship behaviour.
Analysis showed evidence of "complex" inherited genetic variation associated with same-sex sexual behaviour (SSB) seen in the flies.
A "strong paternal effect" with males rather than females passing on the trait indicated a Y chromosome link.
But the genetic influence on survival associated with fruit fly "gayness" appeared to affect females rather than males, causing them to be less fertile.
"Mothers from high-SSB (breeding) lines produced more offspring than those from low-SSB lines," the researchers reported in the journal Proceedings of the Royal Society B.
The scientists, led by Dr Nathan Bailey, from the University of St Andrews, added: "Like any other trait that potentially reduces fitness, the evolutionary maintenance of SSB requires a countervailing fitness benefit.
"Genetic models of SSB have illustrated that such a benefit need not accrue to the individual expressing SSB, but can occur as a result of a fitness advantage specific to the alleles (gene variants) influencing the expression of SSB."
They added that more genetic research across a "broader range of organisms" was required to shed more light on evolutionary theories about the origins of homosexuality.