The Meaning of Human Existence by Edward O. Wilson Read Free Book Online Page A

complex of factors, only some of which are under worker control, determine which female eggs and larvae will become queens.
    For half a century, while data were still relatively scarce, the theory of inclusive fitness was the prevailing explanation of the origin of advanced social behavior. It began in 1955 with a simple mathematical model by the British geneticist J. B. S. Haldane. His argument was in the following form (which I’ve altered here a bit tomake it intuitively easier). Imagine that you are a childless bachelor standing on a riverbank. Looking out over the water, you see that your brother has fallen in and is drowning. The river that day is raging, and you’re a poor swimmer, so you know that if you jump in and save him, you yourself will probably drown. So the rescue requires altruism on your part. But (Haldane said) it does not also require altruism on the part of your genes, including those responsible for making you altruistic. The reason is the following. Because the man is your brother, half of his genes are identical to yours. So you jump in, save him, and sure enough, you drown. Now you’re gone, but half of your genes are saved. All your brother has to do in order to make up the loss in genes is to have two additional children. The genes are the unit of selection; the genes are what count in evolution by natural selection.
    In 1964, another British geneticist, William D. Hamilton, expressed Haldane’s concept in a general formula, which came to be known in later years as the Hamilton inequality. It said that a gene prescribing altruism, such as that of the heroic brother, will increase if the benefit in number of offspring to the recipient exceeds the cost in offspring to the altruist. However, this advantage to the altruist will be effective only if the recipient and the altruist are closely related. The degree of kinship is the fraction of genes that are shared by the altruistand recipient due to their common descent: one-half between siblings, one-eighth between first cousins, and so on in a rapidly declining rate as the degree of kinship becomes more distant. The process later came to be called kin selection. It seemed, at least from this line of reasoning, that close kinship is the key to the biological origin of altruism and cooperation. Hence close kinship is a primary factor of advanced social evolution.
    On the surface, kin selection seemed at first to be a reasonable explanation for the origin of organized societies. Consider any group of individuals that have come together in one manner or another but remain unorganized—a fish school, for example, a flock of birds, or a local population of ground squirrels. The group members, let us say, are able to distinguish not just their own offspring, leading to evolution of parental care by standard (Darwinian) natural selection. Suppose they also recognize collateral relatives related by common descent such as siblings and cousins. Allow further that mutations occur that induce individuals to favor close collateral relatives over distant relatives or nonrelatives. An extreme case would be Haldane’s heroism biased toward a brother. The result would be nepotism, resulting in a Darwinian advantage over others in the group. But where does that lead an evolving population? As the collateral-favoring genes spread, the group wouldchange into an ensemble not of competing individuals and their offspring, but of an ensemble of parallel competing extended families. To achieve group-wide altruism, cooperation, and division of labor, in other words organized societies, requires a different level of natural selection. That level is group selection.
    Also in 1964, Hamilton took the kinship principle one step further by introducing the concept of inclusive fitness. The social individual lives in a group, and it interacts with other members of the group. The individual participates in kin selection with each of the other group members with which it interacts.