A new research has found that the number older brothers a man has, may influence his sexual orientation.
The study of nearly 1,000 heterosexual and homosexual men in Canada, who had either biological or non-biological adopted or step) brothers, was conducted by Anthony Bogaert and colleagues.
In previous studies by Bogaert, he had observed that, on average, a higher number of older brothers correlated with higher likelihood that the individual was homosexual.
This phenomenon is known as the fraternal birth order effect.
Now, Bogaert hypothesised that if rearing or social factors underlie the fraternal birth order effect, then the amount of time a male is raised with older brothers should be predictive of his sexual preference.
Only the number of biological brothers, regardless of whether they were raised together, was important for predicting whether a younger male sibling was likely to be homosexual or heterosexual.
However, other predictors such as time reared with older brothers or the number of nonbiological older brothers did not correlate with the younger male sibling's sexual orientation.