Screams and pant hoots thunder through the forest as the group crashes through the canopy in pursuit of a colobus monkey. After the hunt, they return to the ground, and in the mouth of the alpha male is a large, limp ball of fur. What happens next is gruesome, and the monkey slowly ceases to resemble a monkey. As Ferdinand moves away with his kill, a slew of chimpanzees both young and old trail after him in hopes of securing a piece of the protein-rich snack. Through status alone, Ferdinand can ignore the outstretched palms of his peers with little or no contest. The monkey, a densely caloric food item, will replenish the energy he depleted during the hunt, and he should relish it. Slowly, a grey and elderly female (Sparrow, the oldest in the group) inches past the others, arm extended, and with several gentle grunts politely requests a piece of the meal. In an act that seems to defy all odds, Ferdinand pulls at his kill, extracting a hearty piece of the tail, and hands it to Sparrow. Be it active sharing or tolerated begging, Ferdinand relinquishes a highly coveted resource to an unrelated individual. This, from a biological standpoint, is remarkable.
When an individual’s behavior enhances the fitness of another at a personal cost, it is deemed altruistic. Fitness is a biological proxy for reproductive success, or how effectively an individual transmits his or her genes to the next generation. If chimpanzee A has three offspring that survive until the age of reproduction, this individual has higher absolute fitness than chimp B who has two offspring that live to reproduce, or chimp C who has five total offspring but only two who live to reproduce.
Under the pressure of natural selection, better known as “survival of the fittest”, behaviors that increase individual fitness should evolve. And as would be expected, these behaviors tend to take somewhat of a “selfish” appearance. For Ferdinand, hoarding a colobus monkey makes perfect sense. So why the kind routine?
There are two long-standing theories for the evolution of altruism. The theory of Kin Selection, coined by William D. Hamilton in 1964, introduced the value of relatedness as a means of improving overall fitness . Try thinking of your relatives as bags of shared genetic material; improving their plight means improving your own. If Ferdinand were the son or brother of Sparrow, helping to improve her nutrition might mean that she were more energetically capable of reproducing Ferdinand-like gene bags. But they are not related… so what gives? Perhaps Ferdinand and Sparrow are friends, and this food sharing is a favor returned. The theory of Reciprocal Altruism, articulated first by Robert Trivers  and later refined by Robert Axelrod & William D. Hamilton  suggests that an individual, to the benefit of his or her partner, momentarily reduces its fitness under the expectation that the behavior will be returned sometime in the future. This tit-for-tat would be an economically sensible exchange, so long as one day Sparrow lovingly dismembers a monkey on Ferdinand’s behalf. I’ll keep an eye out for that…
While these predictions have great applicability to much of the animal kingdom, humans (anomalous yet again), demonstrate altruistic behaviors that are incongruous with the theories described above. For example, neither kin selection nor reciprocal altruism would explain charity, a system wherein one donor is willing to suffer a monetary loss in order to aid another, altogether unknown individual. Is it a profound expression of empathy? Adherence to social norms, because others both expect and participate in this behavior? Charting the impressive trajectory of human cooperation relies on an understanding of basal mechanisms, and while evidence suggests that both kin selection and reciprocal altruism play a decisive role in how, when and why chimpanzees behave altruistically, we have much more to learn. And so, in an attempt to chart the origins of human cooperation and conflict management, I follow Sparrow and Ferdinand, hoping for beatings and colobus-killings such that consolation and meat-sharing might ensue– the happy ending to a deceptively morbid dissertation.
 Hamilton, W.D. (1964). The genetical evolution of social behaviour. Journal of Theoretical Biology, 7, 1-52.
 Trivers, R. L. (1971). The evolution of reciprocal altruism. The Quarterly Review of Biology. 46, 35–57.
 Axelrod, R., & Hamilton, W. D. (1981). The evolution of cooperation. Science, 211, 1390– 1396.