From what I can tell (though this varied by culture!) free first born males stayed with the parents. Females were often traded to other tribes (both as war spoils and more peaceful ways). Free second and later sons often discovered the family land couldn't support them and their older brothers families and left looking for anyplace to live (often resulting in war which in turned eased population pressure, though sometimes a city job existed though they were worse than farming until the industrial revolution). Slaves of course had no control of where the children went. The sexism above was real, though how is manifested varied from culture to culture with some worse than others (sometimes it was the oldest female who stayed home).

Genetic diversity requires someone leave their family and join a different one. How that happened varied but nearly every culture recognized siblings having children together resulted in deformed kids and thus developed a culture to prevent that. Every culture includes other animals.