content: transgenderism? if that's true, why arent all sets of identical twins either both trans or both cis, instead of the way it actually is wherein having a set of twins who are both trans is exceedingly rare? I don't know a lot about hormones during fetal development of twins, but wouldn't you expect that if one is getting irregular hormones in the womb then both of them are? if there is a biological cause then all sets of twins should either both be trans or both be cis, since identical twins are genetically identical.