5 - Species Selections on Variability

Summary

SELECTION

We begin with some basic distinctions. Most important is the difference between a process and an outcome of that process; in this case, selection is the process, and evolutionary change is the outcome. The process of selection involves an interaction between an entity and its environment or, more specifically, between a particular trait of an entity and particular aspects of its environment. Part of the fitness calculated for an entity represents the particular value conferred by having a specific trait in a specific environment. In other words, the component of fitness associated with a trait is the representation, in an evolutionary model, of the process of selection.

The selection process itself must be contrasted with the result or outcome of that process. Sorting is simply the differential birth and death of individual entities in a population, while selection is a potential cause of that sorting (Vrba and Gould 1986, p. 217). Sorting at a particular level has a variety of potential causes; it can arise from selection acting at that level or occur as a consequence of chance or of selection processes at either a higher or a lower level.

SPECIES SELECTION

A number of attempts have been made to apply the basic notion of selection to the species level. Vrba, Eldredge, Gould, and others (Vrba and Gould 1986; Vrba 1984; Vrba 1989; Vrba and Eldredge 1984; Stanley 1975; Stanley 1979; Damuth and Heisler 1988) in several articles have defended the idea that selection at a particular level requires characters to be heritable and emergent at that level and to interact with the environment to cause sorting.