“Fitness is essentially a ratio, with the numerator reflecting the success of genes in projecting copies of themselves into the future and the denominator, the success of alternative genes. Since a gene (or an individual, a population, even—in theory—a species) maximizes its success by producing the largest such ratio, it can do so either by reducing the denominator or increasing the numerator. Most creatures, most of the time, find it easier to do the latter than the former, which is why living things generally are more concerned with feathering their nests than de-feathering those of others. Because of natural selection, human beings have a capacity to be peaceful and warlike, cooperative and competitive, loving and violent . . . depending upon conditions. Those conditions include but are not limited to the amount and nature of resources available (such as food, mates, living and breeding space), the nature of social expectation, cultural traditions and indoctrination, degree of embeddedness among kin and other reciprocating individuals, and so forth. Like the proverbial cartoon in which both an angel and a devil perch upon each person’s shoulder, whispering in her ears and vying for attention, our evolutionary heritage offers different routes for future behavior, without necessarily predisposing us in any one direction. Although it is definitely worthwhile to interrogate our evolutionary background for indications as to our predilections, the answer leads us to Jean-Paul Sartre’s famous formulation that human beings are “condemned to be free.” Whether devotees of peace choose to be relieved to learn that we are not biologically obliged to war, or to be distraught that by the same token, we are not unilaterally predisposed, through our biology, to peace, we are all stuck with an obligation (if not necessarily a predisposition) to respond to Sartre’s simple, daunting, existentialist challenge: “You are free. Choose.” WarPeaceHuman Nature Author:David P. Barash