Gulliver ‘s further travels: the necessity and difficulty of a hierarchical theory of selection

Abstract

Abstract For principled and substantially philosophical reasons, based largely on his reform of natural history by inverting the Paleyan notion of overarching and purposeful beneficence in the construction of organisms, Darwin built his theory of selection at the single causal level of individual bodies engaged in unconscious (and metaphorical) struggle for their own reproductive success. But the central logic of the theory allows selection to work effectively on entities at several levels of a genealogical hierarchy, provided that they embody a set of requisite features for defining evolutionary individuality. Genes, cell lineages, demes, species, and clades -as well as Darwin ‘s favored organisms-embody these requisite features in enough cases to form important levels of selection in the history of life. R. A. Fisher explicitly recognized the unassailable logic of species selection, but denied that this real process could be important in evolution because, compared with the production of new organisms within a species, the origin of new species is so rare, and the number of species within most clades so low. I review this and other classical arguments against higher-level selection, and conclude (in the first part of this chapter) that they are invalid in practice for intergenic selection, and false in principle for species selection. Punctuated equilibrium defines the individuality of species and refutes Fisher ‘s classical argument based on cycle time. In the second part of the chapter, I argue that we have failed to appreciate the range and power of selection at levels above and below the organismic because we falsely extrapolate the defining properties of organisms to these other levels (which arc characterized by quite different distinctive features), and then regard the other levels as impotent because their effective individuals differ so much from organisms.