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http://www.telegraph.co.uk/news/mai...ay13.xml&sSheet=/news/2004/10/13/ixworld.html[News Telegraph[/url]
Homosexual link to fertility genes
By Roger Highfield, Science Editor
(Filed: 13/10/2004)
Homosexuality is a natural side-effect of genetic factors that help women to have more children, a study suggests.
A team led by Prof Andrea Camperio-Ciani, of Padua University, found that female maternal relatives of homosexual men seemed to have more children than female relatives of heterosexual men. There was no difference with female paternal relatives.
The finding is based on a survey of 98 homosexual men and 100 heterosexual men and their relatives - 4,600 people in all.
It implies that homosexuals should be more common in societies with declining birth rates, such as Italy, where the influence of this fecundity/gay gene is more significant.
There has been much debate among scientists, based on evidence from twins and families, about why genes have evolved that seem to break the golden rule: that genes persist only because they help us to thrive and pass them on to our descendants.
Prof Camperio-Ciani said he was inspired by a conversation with his 15-year-old daughter, Georgia, who suggested that "this interesting Darwinian dilemma" could be solved if the genetic factor linked with homosexuality could be shown to be linked also with high birth rates.
"This was a brilliant idea and I decided to test it," he said.
Prof Camperio-Ciani, who worked with Prof Dr Francesca Corna and Dr Claudio Capiluppi, emphasises in the Proceedings of the Royal Society, Series B that the team's findings are based on one part of a complex interplay between genes and culture. He suggests that some genetic factors should be linked to the X chromosome (of which men carry one and women two) because earlier work has shown how male homosexuality tends to be on the maternal, not the paternal, line.
The study by the Italian team confirmed a link with the so-called "gay gene", Xq28, which was first identified on the X chromosome by Dr Dean Hamer in America.
It also confirmed an established theory that links homosexuality to the fraternal birth order: homosexual men are more likely to have elder brothers, but not elder sisters, than either lesbians or heterosexual men.
Prof Camperio-Ciani stressed that his study explained only 20 per cent of the variance in sexual orientation of males; otherwise homosexuality would be much more common.
"The remaining 80 per cent has yet to be understood," he writes. "It could - and in fact partly is - due to cultural and individual experience, or even by undiscovered biological factors."
The Padua team speculates that the study could explain why the incidence of homosexuality appears to vary, as it did in ancient Rome where a form of condom was in use.
Prof Camperio-Ciani writes: "When fecundity in general is high because every female reproduces as much as possible, these homosexual genes that enhance fecundity are not expressed significantly.
"But when the population is declining because of a decrease of fecundity (modern Italians) or birth control (ancient Romans), then these factors may well make the difference in relatively promoting fecundity - and therefore homosexuality - in the population."
He adds: "Our findings, if confirmed by further research, are only one piece in a much larger puzzle on the nature of human sexuality. Genetics is nothing without an environment to express it."
Prof Camperio-Ciani emphasised that he had no particular axe to grind in conducting his research. "I am very heterosexual," he said.
Homosexual link to fertility genes
By Roger Highfield, Science Editor
(Filed: 13/10/2004)
Homosexuality is a natural side-effect of genetic factors that help women to have more children, a study suggests.
A team led by Prof Andrea Camperio-Ciani, of Padua University, found that female maternal relatives of homosexual men seemed to have more children than female relatives of heterosexual men. There was no difference with female paternal relatives.
The finding is based on a survey of 98 homosexual men and 100 heterosexual men and their relatives - 4,600 people in all.
It implies that homosexuals should be more common in societies with declining birth rates, such as Italy, where the influence of this fecundity/gay gene is more significant.
There has been much debate among scientists, based on evidence from twins and families, about why genes have evolved that seem to break the golden rule: that genes persist only because they help us to thrive and pass them on to our descendants.
Prof Camperio-Ciani said he was inspired by a conversation with his 15-year-old daughter, Georgia, who suggested that "this interesting Darwinian dilemma" could be solved if the genetic factor linked with homosexuality could be shown to be linked also with high birth rates.
"This was a brilliant idea and I decided to test it," he said.
Prof Camperio-Ciani, who worked with Prof Dr Francesca Corna and Dr Claudio Capiluppi, emphasises in the Proceedings of the Royal Society, Series B that the team's findings are based on one part of a complex interplay between genes and culture. He suggests that some genetic factors should be linked to the X chromosome (of which men carry one and women two) because earlier work has shown how male homosexuality tends to be on the maternal, not the paternal, line.
The study by the Italian team confirmed a link with the so-called "gay gene", Xq28, which was first identified on the X chromosome by Dr Dean Hamer in America.
It also confirmed an established theory that links homosexuality to the fraternal birth order: homosexual men are more likely to have elder brothers, but not elder sisters, than either lesbians or heterosexual men.
Prof Camperio-Ciani stressed that his study explained only 20 per cent of the variance in sexual orientation of males; otherwise homosexuality would be much more common.
"The remaining 80 per cent has yet to be understood," he writes. "It could - and in fact partly is - due to cultural and individual experience, or even by undiscovered biological factors."
The Padua team speculates that the study could explain why the incidence of homosexuality appears to vary, as it did in ancient Rome where a form of condom was in use.
Prof Camperio-Ciani writes: "When fecundity in general is high because every female reproduces as much as possible, these homosexual genes that enhance fecundity are not expressed significantly.
"But when the population is declining because of a decrease of fecundity (modern Italians) or birth control (ancient Romans), then these factors may well make the difference in relatively promoting fecundity - and therefore homosexuality - in the population."
He adds: "Our findings, if confirmed by further research, are only one piece in a much larger puzzle on the nature of human sexuality. Genetics is nothing without an environment to express it."
Prof Camperio-Ciani emphasised that he had no particular axe to grind in conducting his research. "I am very heterosexual," he said.
