The array of living organisms that have populated our planet for the last 3.8 billion years constitute neither William James's infant world of a “blooming, buzzing confusion” (1950: 462) nor the perfect, divinely organized “balance of nature” (Egerton 1973). Rather, it is made up of a diversity of organisms showing an assortment of modes of organization solving the problems of survival and reproduction in a variety of ways. Variation is perpetually produced, and competition and natural selection tune that variation to the biotic and abiotic environment in which a population finds itself. Thus, the diversity of life is not random, but neither is it uniform. The sciences that attempt to characterize living things by means of generalizations and laws, common functions, and the operation of a few central mechanisms must face up to the complexity of this domain.
Natural selection, while a major force, is not the only cause of the diverse forms of life. And natural selection can operate at different levels of organization either in concert or in opposition. Attempts to unify the theories of evolution by appeal to a single, privileged unit of selection fail to do justice to hierarchical selection regimes. The first section in this chapter addresses this defining issue in the philosophy of biology and councils pluralism.