[iacopo.russo (OP)]

A listener wrote to us to ask:

Hi! There are people who identify as e.g. bisexual, homosexual etc. Is it possible that it is also biologically linked?

What do you think?

[alancalverd]

In humans: not as far as anyone knows. Among birds: some possibility of a genetic predisposition to anomalous sexual preference (expressed as triple parenting) in some species. 

[Petrochemicals]

Hormones in the foetal stage.