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Background and History
Beginning with French philosopher Jean-Jacques Rousseau, anthropology and psychology had become imbued with the myth of the Noble Savage. Like fellow philosopher Thomas Hobbes, Rousseau believed men to be equals by nature and driven by their passions, but not inexorably toward conflict as Hobbes had proposed. Instead, in the absense of the "unnatural" institutions that pervade civilization, like monogamy and private property, conflict would be worked out peacefully, and harmony maintained. [NOTE: needs lots of work]
During the late 19th and early 20th century, voluminous unsympatheic observations of prestate societies had accumulated during the hey-day of European imperialism. For the first time, anthropologists ventured into the wilderness, living among their subjects for months or years, and cataloged societies in great detail with their own eyes. Additionally, the ever-growing body of archeological data made it nearly impossible to claim, as some had no more than half a centry earlier, that human prehistory was peaceful, and warfare a disease of the modern age.
The conclusions of these researchers speak volumes. Otterbein (1989), drawing on a sample of fifty societies, found only five that engaged in warfare "infrequently or never". Even in those five cases, the societies in question were in fact refugees from conflict, driven into isolation and thus buffered from further confrontation. Similarly, Jorgensen (1980) looked at 157 North American indian tribes, finding that only seven could be considered peaceful, and again, those seven were geographically isolated from other peoples.
War and Kin Selection
War, Status and Resources
War and Runaway Sexual Selection
As noted by Ronald Fisher, if females have a strong preference for a particular male phenotype, confering some advantage not due to said preference initially, the female preference will continue to increase through sexual selection as long as the sons of females exerting the preference have an advantage over other males. This will result in "runaway" sexual selection, where both the phenotype and female preference grow enormously. It may seem unusual, but male advertisements of this sort are typically costly to maintain and thus serve to show potential mates all their genetic cards, so to speak. This can even be true with potentially lethal behaviors, as long as the female preference for the phenotype is stronger than the pressures exerted by natural selection against it.
Thus, Low (2000) proposes that perhaps, as among the Yanomamo whose reproductive success depends in large part on being a skillful warrior, humans have faced a long history of runaway sexual selection for aggressive warfare. To the extent that women in modern societies have a preference for "war heros" warfaring behaviors could still be selected for, or at least maintained.
Child Abuse and Infanticide
Prior to the 1980's, little was known about the relationship between genetic relatedness and child abuse. In 1976, at a weekly seminar discussing E.O. Wilson's Sociobiology, a graduate student named Suzanne Weghorst posed an interesting question following from ethological studies in non-humans: if, as Hrdy observed in langurs and other primates, and Powers in birds, kinship correlations were an important criteria in infanticide, might it also explain the abuse of human children? After evaluating the available literature, she reported back that, unfortunately, there was no evidence one way or the other (Daly & Wilson, 1998).
Although identifing increased risk due to kinship differences is hard to determine from the available national statistics (US Census and the FBI do not distinguish between step and biological parents), Daly and Wilson investigated the question in a number of other populations. What they found was shocking. The rates of murder are much higher for stepparents than for genetic parents, from 40 to 100 times higher for preschool aged children, with the risk decreasing sharply with age. To get some idea, the number of 15-17 year olds killed by stepparents is roughly the same as the number of 0-2 year olds killed by genetic parents. The number of 0-2 year olds killed by stepparents, however, is well over 600 per million child-years of parent-child coresidence, while it doesnt even reach 30 for genetic parents (Daly & Wilson, 1988).
Jorgensen, J. 1980. Western Indians. Freeman.
Low, B. 2000. Why sex matters: A darwinian look at human behavior. Princeton University Press.
Otterbein, K. 1989. The evolution of war: A cross-cultural study. HRAF press.