Inclusive Fitness and Forager Aggression

In 1964, biologist William Hamilton suggested that the degree of biological relatedness between individuals affects the manner in which they interact with each other. The more closely individuals are related, the more helping, sharing, and caring should be expected. Alleles are alternative forms of a particular gene, and due to common inheritance, relatives are likely to have many identical alleles. Helping relatives is an indirect way of enhancing one's own fitness—hence the concept is known as inclusive fitness.12

The inclusive fitness concept has the potential for elucidating some aspects of aggression among nomadic hunter-gatherers. Inclusive fitness theory predicts that close relatives will come to each other's aid during aggressive conflicts.13 We have seen an example of such aid as an Alacaluf brother assisted his sibling in a murderous maneuver to recoup a wife.14

I think, however, the application of inclusive fitness theory to conflict situations in humans has been too narrowly conceived as fighting support. "Aiding" a relative in an aggressive situation should not automatically imply that fighting shoulder to shoulder is the only or best tactic as weighed by inclusive fitness enhancement. Perhaps a more effective aid-giving approach, in some circumstances, involves talking some sense into an infuriated relative and dragging him away from a risky situation. I am reminded of the idea behind a slogan used in the United States intended to reduce drunk-driving tragedies: "Friends don't let friends drive drunk." In this case, kin don't let kin fight foolishly. My speculation is based in part on a recurring theme in ethnographic accounts: In nomadic bands, and also in other types of societies, third parties routinely distract and separate disputants. How does inclusive fitness theory apply here? In nomadic band society, third parties are generally relatives to some degree of one or both antagonists.

Inclusive fitness theory also leads to the prediction that biological relatives should not kill or harm one another.15 Seemingly counter to this prediction, we have seen that a Netsilik man killed his violent, insane brother and that one of the two Siriono killers threw a wooden club from a tree, killing his sister. In the Netsilik case, the entire family and other members of the band saw the act as necessary for the safety of everybody. In short, this is an unusual situation wherein the victim, while a relative, represents a deadly threat to all his other relatives. As mentioned, the Siriono killing may have been an accident. These two incidents reinforce a broader epistemological point. In attempting to assess overall patterns, we should not lose sight of the forest when confronted by an occasional exceptional tree. Unfortunately, ethnographic reports are often sketchy as to the degree of relatedness between killer and victim, but regarding the Ju/'hoansi, Lee specifies that the closest biological relationship between killer and victim was nephew and uncle: "Close kin do not kill one another."16 Given the fact that biologically related family members are regularly in proximity to each other in band society, Ju/'hoansi killings would seem to disproportionately represent nonkin and distant kin over close family members.

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