Anthropologists have long found associations between the rate of polygynous marriage within a society and its likelihood to wage war on neighboring groups or tribes, as well as its internal violence and homicide rate. Violence can actually cause polygyny, as warrior societies lose a lot of young men in conflict, leaving many more surviving women than men. As a result, some women face the unenviable choice of either sharing a husband or not marrying at all.

Often, ancient warfare would involve raiding other villages to capture fertile women as brides. The strongest, most war-adept groups of men can defend their own villages and women, raid other villages and capture brides. The fiercest groups quickly become the most polygynous, with the fiercest warriors taking the most wives.

Polygyny can also cause violence. For every man with two wives, there is on average another man will never marry. For each ancient king with 1001 wives or concubines, perhaps a thousand other men never had a family of their own. Polygyny, an excess of males, and gross economic inequality can all raise the number of men who end up siring no children at all. These millennia of sexual selection, in which the genes of these evolutionary losers have been eliminated by natural selection, helped created the same "problem with men" that led us to Jacob Zuma.

Remember that our ancestors include those men who strove for wealth and power, and especially those men who strove hardest when the differences between winning and losing grew widest. We are far less likely to have descended from the evolutionary losers or inherited their losing genes. This long history of selection has, in other words, guided our evolution such that the greater the inequality in a society, the more frantically men will strive to come out on the top end of it. And all this striving leads to competitiveness, including the perpetuation of inequality and, at times, violence.

Analyses of North American homicide statistics by evolutionary psychologists Martin Daly and the late Margo Wilson found that being a young man presents the greatest single risk factor for either committing or suffering homicide. The same is true in every society for which they were able to find data. They wrote that most homicides in which men kill men are "rare, fatal consequences of a ubiquitous competitive struggle among men for status and respect."

At an evolutionary level, the essential dilemma of masculinity is to avoid becoming one of those unfortunate souls who either dies young or lives out his days without reproducing. Biologists call this "zero fitness," meaning they have passed on none of their genes. Inequality within a society drives men -- especially young, poor men of relatively low social status -- to act aggressively and take big risks in order to improve their prospects, first to avoid joining the zero-fitness males, and then to become one of the few men who have historically produced the larger share of descendants. Not only does inequality among men lead directly to polygyny, but both inequality and polygyny further entrench the intensely competitive conditions in which violence and misogyny thrive.