"Studying individual differences in gender and sexual orientation provides insight into how early-life biology shapes the brain and behaviour," says the developmental psychology researcher.

VanderLaan's study assessed whether biomarkers--markers of early-life biological processes--work in conjunction with each other to contribute to male same-sex sexual orientation or influence sexual orientation independently of one another.

But our study considers whether there is some interaction or association between these influences," says VanderLaan.

The biomarkers VanderLaan examined included participants' number of older brothers, rate of left- versus right-handedness, and the presence of gay and/or bisexual male relatives in their families.

VanderLaan's group used latent profile analysis (LPA), a statistical technique, to help identify whether these biomarkers cluster together in the same individuals or are present in only particular subgroups of men.

The study found evidence for at least four different subgroups: men with elevated numbers of older brothers, men with a greater degree of non-right-handedness, men with elevated gay and/or bisexual male relatives, and men with low levels of these biomarkers.

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