Fridae

According to news reports, a study conducted by a group of Italian researchers has found that homosexuality is a natural side effect of genetic factors that help women to have more children.

A team led by Prof Andrea Camperio-Ciani, of Padua University, found that the mothers, aunts and sisters of gay men tend to have more children than female relatives of straight men. The difference is not seen in female paternal relatives.

The scientists surveyed 98 homosexual men and 100 heterosexual men and their relatives - 4,600 people in all - in northern Italy.

The studies published in the Proceedings of the Royal Society B: Biological Sciences also confirmed an established theory that gay men are more often the younger siblings of a number of older brothers, but not elder sisters, than either lesbians or heterosexual men.

Researchers said the genetic components are linked to the X chromosome which is inherited only from the mother. But they are probably on other chromosomes and could partly explain male homosexuality.

"The key factor is that these genes both influence homosexuality in men, higher fecundity in females and are in the maternal and not the paternal line," Andrea Camperio-Ciani, who headed the research team, said in an interview.

Other than greater fertility in the female relatives of gay men, the researchers also found a greater number of gay men in the maternal line of the family.

An early interest in sex before the age of 10 was also a predictor of homosexuality, according to the researchers.

"We can no longer say that is it impossible to have a gene that influences homosexuality because we found out that genes might have different effects depending on gender," Camperio-Ciani. But he added that cultural and individual experience also play a part.

In 1993, US researchers suggested male homosexuality was passed from mother to son after they found strong patterns of inheritance in family trees. Scientists said it might be that the mother develops some kind of resistance to the male Y chromosome in her offspring that makes subsequent baby boys more likely to be born gay. Other researchers have however been unable to replicate these findings.

In a BBC interview, Alan Wardle from the gay rights charity Stonewall said: "This is an interesting debate and there may well be a genetic element, but it's not conclusive.

"It does not really matter whether it is nature or nurture.

"The important thing is getting equality for homosexual people."