Gay Biology

(Toronto, Ontario) A new study suggests a male's sexual orientation is not the product of his environment but rather is influenced by biological factors present before birth. 

Researchers at Brock University in St. Catharines, Ont., have found evidence that "a prenatal mechanism(s) . . . affect men's sexual orientation development."

The study's author, Prof. Anthony F. Bogaert, explored the causes behind what is known as the fraternal birth order, research that shows a correlation between the number of biological older brothers a man has and his sexual orientation.

But that concept leaves unclear whether older brothers have a socializing effect on sexuality, or if biological factors are at play.

Bogaert's study, which will be published this week in the journal Proceedings of the National Academy of Sciences, argues for the so-called nature, instead of nurture, explanation of homosexuality.

"These results support a prenatal origin to sexual orientation development in men and indicate that the fraternal birth-order effect is probably the result of a maternal `memory' for male gestations or births," Bogaert writes.

Bogaert, who teaches in both the community health science and psychology departments at Brock, studied more than 900 heterosexual and homosexual men in Canada who had either biological or non-biological brothers.

Dividing his sample into four groups, Bogaert examined the impact of all types of older brothers, including step and adopted siblings, and the amount of time brothers spent together while growing up.

His research found that only the number of biological brothers had an impact on sexuality, regardless of whether the boys were raised together.

"The number of biological older brothers, including those not reared with the participant . . . increases the probability of homosexuality in men," the study reads.

Bogaert also found that the amount of time being raised with older brothers did not influence a younger sibling's likelihood of being gay.

Writing a commentary piece accompanying Bogaert's study, professors from Michigan State University noted that his research puts to lie the notion that one's social environment can affect sexuality.

"It is the number of older biological brothers the mother carried, not the presence of older brothers while growing up, that makes some boys grow up to be gay," write David Puts, Cynthia Jordan and Marc Breedlove.

Bogaert's study, entitled Biological versus nonbiological older brothers and men's sexual orientation, was published Monday in an online version of the PNAS journal.

*by The Canadian Press