Some creatures are monogamous. Some creatures are not. Some creatures eat their young. Some creatures are solicitous of the young of others. Other higher pr

Some creatures are monogamous. Some creatures are not. Some creatures eat their young. Some creatures are solicitous of the young of others. Other higher primates do not seem to be monogamous, but I recall reading that there is a greater chance of the male of the species being involved if they feel they're defending their child. If so, this might/would have provided positive evolutionary pressure. Similarly, being altruistic enough to let grandparents or other older members of the tribe survive let to evolutionary advantage (knowledge transfer, for example). It's only been a few 10K years so we're still the wonderful cro magnons that showed up in the middle east and started shoving the other Humans aside.