Humans are complex and are governed by more than simple socio-biology, as such no individual can be predictable. But the behaviour of general populations can be. At the nasty end of Socio-biology you have the "Baby P" situation. Where this happens it is almost always the case that the infant is abused to death by the male partner who is not the biological father while the biological mother does little to intervene. Just like Lions do when they take over a pride and kill all the cubs that are not theirs and the lionesses sit back and let them do it. Some people are just more driven by their instincts than others.