The Waorani may have the highest rate of homicide of any society known to anthropology. We interviewed 121 Waorani elders of both sexes to obtain genealogical information and recollections of raids in which they and their relatives participated. We also obtained complete raiding histories of 95 warriors. An analysis of the raiding histories, marital trajectories, and reproductive histories of these men reveals that more aggressive warriors have lower indices of reproductive success than their milder brethren. This result contrasts the findings of Chagnon [Chagnon N (1988) Science 239:985-992] for the Yanomamo. We suggest that the spacing of revenge raids may be involved in the explanation of why the consequences of aggressiveness differ between these 2 warlike lowland South American peoples.lowland South America ͉ warfare ͉ Yanomamo I n 1988, Napoleon Chagnon (1) published evidence indicating that, among the famously warlike Yanomamo of Venezuela, living men who were labeled as unokai for having undergone a rite of purification after participating in a homicide had significantly more wives and children than their less bellicose brethren. The suggestion that more aggressive males enjoyed an individual fitness advantage over milder men provoked an unusual amount of comment and response, both from scholars with significant field experience among the Yanomamo and other warlike tribal societies (2-10), and from armchair anthropologists and the popular press. The investigation reported here is not an evaluation of Chagnon's model per se, or an attempt simply to replicate his study within another society. Rather, it is an exploration of what appears to be the most contentious of the issues raised by his article and its critics, namely that the presence or absence of fitness differences among men correlates with differences in aggressiveness. The data used here, collected during the Waorani Life History Project (WLHP), come from the Waorani of Ecuador, a people even more warlike than the Yanomamo.Although Chagnon (1) was careful to assert that ''the argument that cultural success leads to biological success among the Yanomamo might be the most promising avenue of investigation to account for the high reproductive success of unokais,'' much of the critical response to his article took a more extreme stance. Chagnon's critics argued that he contended that natural and/or sexual selection worked among the Yanomamo to promote alleles for aggressive behavior-that is, that microevolution was selecting for male aggressiveness. The present study of the Waorani addresses the basis for the unusually fierce criticism of his article.To avoid some of the methodological objections raised to Chagnon's work, we included in our sample of warriors both living and dead men; we ranked their aggression by the number of raids they participated in and not by a local term of contested meaning with which they are labeled. Our analysis is free of the problem caused by the inherent correlation of the warrior's age with both participation in raids ...

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Human adaptation depends upon the integration of slow life history, complex production skills, and extensive sociality. Refining and testing models of the evolution of human life history and cultural learning will benefit from increasingly accurate measurement of knowledge, skills, and rates of production with age. We pursue this goal by inferring individual hunters' of hunting skill gain and loss from approximately 23,000 hunting records 20 generated by more than 1,800 individuals at 40 locations. The model provides an improved picture of ages of peak productivity as well as variation within and among ages. The data reveal an average age of peak productivity between 30 and 35 years of age, though high skill is maintained throughout much of adulthood. In addition, there is substantial variation both among individuals and sites. Within study sites, variation among individuals depends 25 more upon heterogeneity in rates of decline than in rates of increase. This analysis sharpens questions about the co-evolution of human life history and cultural adaptation. It also demonstrates new statistical algorithms and models that expand the potential inferences drawn from detailed quantitative data collected in the field.Ohtsuka 1989) while others do not (Bird and Bliege Bird 2005).

Human adaptation depends on the integration of slow life history, complex production skills, and extensive sociality. Refining and testing models of the evolution of human life history and cultural learning benefit from increasingly accurate measurement of knowledge, skills, and rates of production with age. We pursue this goal by inferring hunters’ increases and declines of skill from approximately 23,000 hunting records generated by more than 1800 individuals at 40 locations. The data reveal an average age of peak productivity between 30 and 35 years of age, although high skill is maintained throughout much of adulthood. In addition, there is substantial variation both among individuals and sites. Within study sites, variation among individuals depends more on heterogeneity in rates of decline than in rates of increase. This analysis sharpens questions about the coevolution of human life history and cultural adaptation.

A critical examination of Gross's hypothesis that aboriginal Amazonian populations were limited to low levels by lack of adequate protein resources concludes that (1) evidence either f o r or against the hypothesis is still in short supply; (2) the role of vegetcble protein in abonginal diets needs much more attention and may ultimately overthrow the proteinlimitation hypothesis; (3) the abundance of animal protein in the tropical forest has likely also been underestimated; (4) the abundance of people in precontact Amazonia may well have been underestimated as well. [Amazonia, protein, cultural ecology, limiting factors, population]. GROSS (1975) HAS ARGUED that the size, permanence, and density of aboriginal settlements in the Amazon basin were and are limited to low levels-for the most part the levels manifested today by the surviving indigenous peoples -by insufficient protein resources. This paper takes issue with that claim and submits that the evidence to support Gross's conclusion is fragmentary and ambiguous enough to permit a contrary claim: that, currently at least, protein sources may be underexploited in the Hylea. (Gross has cast the argument in the best possible way by directing attention not only to the broad category "protein" but, more specifically, to the crucial matter of the relative proportions of the essential amino acids, which determine the quality of any protein in human nutrition. That vital information is utterly lacking for many of the protein foods discussed below, but if the issue is raised in anthropological circles, we may eventually gain the missing data.) I want to stress at the outset that I am not hostile to the idea of protein limitation of human populations per se. In fact, I have argued (Beckerman 1977) that precisely such a mechanism as Gross suggests did indeed limit the size of the populations inhabiting some of the Polynesian islands. The difference is that in the Polynesian case we have (1) a situation in which the flora and fauna are notably impoverished, for good biogeographical reaons; (2) a situation that therefore provides us with a good a przori reason to suspect that a limitation of resource alternatives may have been an important factor in the population dynamics of the people involved; (3) 533

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The root of modern human warfare lies in the lethal coalitionary violence of males in small-scale societies. However, there is a paucity of quantitative data concerning the form and function of coalitionary violence in this setting. Debates exist over how lethal coalitions are constituted, as well as the motivations and benefits for males to join such groups. Data from a lowland Amazonian population, the Waorani of Ecuador, illuminate three issues: (i) the degree to which raiding parties are composed of groups of fraternal kin as opposed to strategic alliances of actual or potential affinal kin; (ii) the extent to which individuals use pre-existing affinal ties to motivate others to participate in war or leverage warfare as a mechanism to create such ties; and (iii) the extent to which participation in raiding is driven by rewards associated with future marriage opportunities. Analyses demonstrate that Waorani raiding parties were composed of a mix of males who were potential affines, actual affines and fraternal kin, suggesting that men used pre-existing genetic, lineal and social kin ties for recruiting raid partners and used raiding as a venue to create novel social relationships. Furthermore, analyses demonstrate that males leveraged raiding alliances to achieve marriage opportunities for themselves as well as for their children. Overall, it appears that a complex set of motivations involving individual rewards, kin marriage opportunities, subtle coercion and the assessment of alliance strength promote violent intergroup conflict among the Waorani. These findings illustrate the complex inter-relationships among kin selection, coalition building and mating success in our species.