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Humans live in environments that are even more challenging than the jungle habitats of chimpanzees, but we can cope in such environments because our greater brain/body size permits us a degree of inventiveness unsurpassed in the animal kingdom.
However, we have needed to retain bonobo-like cooperation in order to survive, particularly in hostile environments.
Further, our greater brain/body ratio has imposed an inordinately long, parent-dependent childhood, and this has necessitated prolonged male-female pair-bonding such as is innate in many bird species, but which is not characteristic of chimp or bonobo societies.
Having fathered a child, a human male can only ensure the perpetuation of his genes (reproductive success) by staying close enough to ensure survival of his offspring and/or by fathering children with many women. Men might, by their emotional/sexual nature, opt for both strategies, but society has long imposed a cost on fathering. So, official polygamy has traditionally been the exclusive reserve of the wealthy.
Human females could similarly ensure reproductive success (survival of their children) by nuturing each child and by mating with several fathers (ensuring a variety of genetic possibilities for her offspring). However, human males, like the males of many species, are typically less invested in the survival of the offspring of other males, so human females can best secure the survival of their children by maintaining the support of one male.