Having Multiple Older Biological Brothers Found to Be a Factor in Male Homosexuality

There is new information available that may help to answer the age old "nature versus nurture" question regarding male homosexuality. According to a recent Canadian study published in the journal Proceedings of the National Academy of Sciences, men are more likely to be homosexual if they have biological older brothers. This most recent study, which supports the findings of more than a dozen previous clinical investigations, found that a man's sexual orientation is affected by his birth order, and the number of older brothers he has. No corresponding link has been found in lesbians.

Where results of the current Canadian study expand on the findings of the previous research is in its determination that the link between male homosexuality and fraternal birth order is biological, and not environmental.

The study, which examined the family structures and sexual orientation of 1,000 Canadian men, did not just study men who had grown up with their biological families, but included blended families and families created through adoption, as well as families where the men were not raised with their biological mothers or with their biological older brothers. The study looked only at the number of number of biological brothers the mothers of the men in the study had carried before them to determine whether or not there was a genetic link to be found between their birth order and their sexual orientation.

The results indicated that there was no discernible difference between the likelihood of a man with multiple older brothers who grew up in the company of his biological family to be homosexual from that of a man with multiple older brothers who did not. These findings have prompted speculation that the causation of the connection between fraternal birth order and male homosexuality is developed somewhere in gestation.

The study, conducted by Anthony Bogaert, a social psychologist at Brock University in St. Catherine's, Canada, is the first to study only biological factors involving the incidence of male homosexuality and the number of older brothers the subject has.

Bogaert's hypothesis, based on his research, is that the answer to the question probably lies in what he refers to as "maternal memory." He theorizes that the mother's body may remember how many male children she has carried through gestation, and that somewhere therein is the link to occurrence of male homosexuality. The more male children she has carried, the greater the likelihood of baring a homosexual son. These findings were also noted to be more pronounced in younger mothers.

Although the findings are indicative of a connection, however, they are not a comprehensive explanation of the biological nature of homosexuality. In the study published by Bogaert, fraternal birth order was reported to account for sexual orientation in one out of seven homosexual men, determining no causation for the remaining six. Nor do the findings determine any way of predicting whether or not a woman is more likely to carry a homosexual child.

According to the study, for each biological older brother that a male child has, the likelihood of his being homosexual increases by approximately three percent.

Source: CanWest News Service