Originally Posted by
Alextanium
Look at it this way: Mother birds that were less inclined to guard their eggs had them eaten by predatory species, hence they didnt have as many children, and their lines died out. Mother birds that had genes which coded for more maternal nurturing behaviour towards eggs would ensure their eggs survived maturation, so their offspring would live, passing on the genes for being more maternal to their own eggs.
Same goes for sex. Those that don't want to have sex, don't have sex and don't pass on their genes. Those that do, do. And sex is the ultimate pleasure vs pain reward system in nature. We do it because it feels good.
Assassins Creed is fiction. Your ancestors memories are not coded in your DNA.