Oxytocin release in females with an infant may lead to increased aggression towards males.

“and we speculate I think it's the hypothesis that um because oxytocin is released when you've got an infant basically for females uh males are a bigger threat then because in many primate societies and other mammals uh males sometimes can be infanticidal because if they kill off a female's infant that's you know then that will bring that female into uh receptivity for mating much more quickly and so so that's sort of The evolutionary yeah it is brutal The evolutionary rationale behind that so that's kind kind of our supposition”