primogeniture is a selective pressure for incestuous practices :theory-gary:

jk its not always cast favorably, in those cases its an easy cautionary tale because its taboo. 'be careful where you stick your dick or its gonna end up in your mother/daughter/sister'. which is pretty absurd but a clear message of anti sexual aggression. just the other day on this very board some people were talking about piggish men & the messaging of 'how'd you like your sister/mother get catcalled' was used there; its the same stuff.