A further parallel between chimpanzees and small scale human societies comes from analyses of two extreme warring societies, the Waorani of New Zealand and the Yanomamo of Venezuela. Though violence accounts for between 40-55% of all deaths in these two groups, attackers appeared immune to injury, with no more than 5% dying in battle, and often no deaths at all. Chimpanzee attackers are likewise immune to injury, due in large part to the strategic use of imbalances of power. The parallels between chimpanzees and humans living in small scale societies supports the idea that similar pressures favored the capacity for coalitionary killing in both species. Does this mean that each of these species should always kill in this way, and thus, as argued by Ferguson, the archaeological record should be chock full of deaths by coalitionary attackers? To argue for this position is to misunderstand the nature of an adaptation, and the arguments put forth by Wrangham as well as the evolutionary psychologists Martin Daly, Margo Wilson, and David Buss. As I discussed earlier on in this chapter, adaptations are contingent upon particular environmental circumstances. What is adaptive today need not be tomorrow. This is why it is not only unsurprising to see variation in the frequency of coalitionary killing among chimpanzee sites, among humans living in small scale societies, and among modern day humans who sometimes kill their spouses, stepchildren, and rivals, but predicted by evolutionary theory. Adaptations are economically efficient solutions to particular social or ecological problems. If those problems or pressures change, the original adaptation may have no impact on survival or a negative impact. A hiatus in the archaeological record — assuming this is the last word — is interesting with respect to the conditions that might favor or select against coalitionary killing, but in no way undermines the logic of an evolutionary adaptation, one shared by chimpanzees and humans. T