Originally Posted by noparlpf
I did say by the time the infant weans, because the mother's hormones still affect the infants until then. Do these studies on identical twins take into account whether they're breastfed or whether they receive other food? That might be interesting to look into.
Going by the studies with identical twins, environment must factor in somehow, but when? Many children's sexualities are fairly clear at around six or eight.
In general, the studies look at twins separated at birth (something that has mercifully mostly stopped now), so none of them were breast fed.
Early childhood experiences can strongly affect sexuality in general. There is, for example, the famous Westermarck effect, which causes children to assume any other child they grew up with to be a sibling, and so not sexually attractive. This came to be a problem in the Kibbutzim of Israel, where children were raised communally, and so none were attracted enough to each other to marry! On the other hand, we tend to desire people who look similar but not identical to the primary caregiving adults in our young years, which is why many straight men/gay women end up with women who look vaguely like their mothers and gay men/straight women often end up with men that look like their fathers.