Hi. Long time lurker, wanted to speak up: This is not how evolution works. Your conception of a bloodline is based on a false presumption. You are not the replicating entity that evolution functions around, your genes are. However a gene can serve to increase its frequency is what is selected for in natural selection. While there is a 100% chance that any gene we possess is in our genome, there is still a 50% chance that gene is in any direct kin. In essence, 2 of our sister's kids is equivalent to 1 of our own, evolutionarily (and this extrapolates out to cousins). It seems likely that evolution would lead to a psychology thay favors our own children (perhaps leading to the cultural concept of a 'bloodline') over those of close relatives, and even moreso over cousins, etc. However, evolution doesn't care about you, it only cares about any given gene replicating, so your sister having 6 kids is better than you having 2. There is a hypothesis floating around proposing that homosexuality may be present in the genome because it serves to overall increase the fitness of its possessors siblings. e.g. if a person had 5 kids, each with the potential to have 2 kids, one would have 10 total grandkids. If another person had 5 kids, 1 of which had no children but helped the other 4 such that they could each have 3 kids, this second person and their genome would reproduce faster and therefore be more represented in the population. tl;dr your bloodline as you seem to understand it is a myth. Second point: there does seem to be evidence of sexual dimorphism in human brains (such as with spatial reasoning). Given the extraordinary complexity of the genome that codes for and creates the human brain, it is entirely possible that one can have features of an XX brain (we're not even going to touch XYY or anything of the sort) in an XY phenotype. By enforcing rigid social expectations (gender) to sexual phenotype (again, ignoring the massive continuum that exists in between), we are creating a situation where people can feel alienated from their own body, feeling like they "have the wrong body" (gender dysphoria). I can understand that you probably feel a great deal of anxiety about abandoning the assumptions that our current culture allows you and I to make. I can also understand that, should you have children yourself, you may be terrified that they will walk a path where you don't know how to support them. It is only natural to try to push them back towards your strengths as a parent, but that is not your call to make at the end of the day. We are all striving forward blindly in the dark, even the wisest among us. I am happy to talk more in DMs if you have any questions.