A new Canadian study has added further weight to the theory that sexual orientation is influenced by biological factors in the womb, not the environment in which a child is reared.
The report explores the cause of the previously established link between the number of older brothers a man has and his sexual orientation; the more brothers a man has the higher the likelihood of his being homosexual.
Some thought that the effect of bringing up a child in a household with older siblings could somehow have an impact on sexual orientation.
However, the study’s author, Prof. Anthony F. Bogaert of Brock University in St Catharines, Canada, says his research rather suggests that there is probably a biological basis for the phenomenon and in turn, homosexuality.
More than 900 heterosexual and homosexual men who had either biological or non-biological brothers were studied in the research. All kinds of factors were considered including step and adopted brothers, as well as the amount of time brothers spent together while growing up.
He found that it is only men with older biological brothers who have an increased probability of homosexuality – even when the brothers were not raised together. Men that were brought up with older step or adopted brothers did not show an increased chance of being gay. This suggests a strong biological basis for the older brother and homosexuality link.
The effect is statistically significant in research terms, but Bogaert points out that 95 percent of men with older brothers are heterosexual.