[NOTE: The full text of the journal article is available here.]
An Oct. 3, 2004 article published by Reuters and CNN reported:
"Genetic factors, along with cultural and early experiences, influence male homosexuality, Italian scientists said on Wednesday.
Researchers at the University of Padua 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.
More than a decade ago scientists in the United States reported that they had found evidence of a 'gay gene' in men. But other researchers questioned the finding when they could not duplicate the results.
Camperio-Ciani and his team suggest there [are] several genes could be involved, including those on the X chromosome.
In their research, which is reported in the Proceedings of the Royal Society, they found an increase in homosexuality in the maternal line of gay men they studied which suggests the X chromosome.
'We know that at least one of these genetic factors in on the X chromosome but that is not enough, there must be other genetic factors that are important but are elsewhere,' Camperio-Ciani added.
The results are based on a study of 98 homosexual and 100 heterosexual men and about 4,600 of their relatives. The scientists compared the frequency of gay men on the maternal and paternal lines of the families.
Among homosexuals there were a greater number of gay men in the maternal line of the family, as well as greater fertility in the female relatives.
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." Oct. 13, 2004 CNN & Reuters
Regarding their soon-to-be published article "Evidence for maternally inherited factors favouring male homosexuality and promoting female recundity," (by F Corna, A Camperio-Ciani and C Capiluppi) the Proceedings of the Royal Society, states on their website (Oct. 13, 2004):
"The question of whether homosexuality has a genetic foundation can provoke fierce debate. A strong opposition to the genetic explanation is the Darwinian paradox: a genetic factor that reduces reproductive success should progressively disappear from the population.
The authors here argue genetic factors could partially explain male homosexuality, and propose a paradox solution: genetic factors favouring homosexuality in males could increase fecundity in females, recovering the loss of fitness.
They suggest these factors should be partly bound to the X chromosome, because male homosexuality, associated with increased female fecundity was found only in the maternal and not in the paternal line of homosexuals." Oct. 13, 2004 Proceedings