The Nature of Selection is a straightforward, self-contained introduction to philosophical and biological problems in evolutionary theory. It presents a powerful analysis of the evolutionary concepts of natural selection, fitness, and adaptation and clarifies controversial issues concerning altruism, group selection, and the idea that organisms are survival machines built for the good of the genes that inhabit them. "Sober's is the answering philosophical voice, the voice of a first-rate philosopher and a knowledgeable student of contemporary evolutionary theory. His book merits broad attention among both communities. It should also inspire others to continue the conversation."-Philip Kitcher, Nature "Elliott Sober has made extraordinarily important contributions to our understanding of biological problems in evolutionary biology and causality. The Nature of Selection is a major contribution to understanding epistemological problems in evolutionary theory. I predict that it will have a long lasting place in the literature."-Richard C. Lewontin
The work of Ronald Fisher (who developed the required mathematical language and wrote (1930)), (who introduced the concept of the "cost" of natural selection), (who elucidated the nature of selection and adaptation), (who established the idea that mutation, by creating genetic diversity, supplied the raw material for natural selection: see (1937)), (who conceived of kin selection), (who recognised the key importance of reproductive isolation for speciation: see (1942)) and many others together formed the modern evolutionary synthesis. This synthesis cemented natural selection as the foundation of evolutionary theory, where it remains today.
A more fundamental reason for a discussion of drift here in an entryon natural selection is the view that drift is the zero-forcebackground against which evolutionary forces, including naturalselection, act (Brandon 2006). Just as in Newtonian mechanics onecould not properly understand the notion of gravitational force,without understanding Newton's 1st Law, similarly onecannot understand natural selection in evolutionary biology withoutunderstanding the background against which it operates. Put inother terms, drift provides the appropriate null hypothesis againstwhich to test any selection hypothesis. Unfortunately this is notalways well understood. Indeed this way of thinking aboutevolution stands some canonical versions of evolutionary theory ontheir heads. For instance, those who would take theHardy-Weinberg Law as a Zero-Force Law of evolution (see, e.g., Ruse1973, and Sober 1984, but also many standard textbooks in evolution)view stasis as the default state of evolutionary systems, with someevolutionary force needed to move (i.e. evolve) them. Without anet force, no net change. But all modern methodology in molecularevolution is predicated of the truth of just the opposite idea, namelythat left alone evolutionary systems drift. Drift is the defaultstate. So that, for instance, neutral alleles in differentpopulations differentiate from each other. But this moleculartruth is iterated throughout the biological hierarchy. Oncespeciation occurs, species differentiate (drift apart) as a nullexpectation. Which is not to say that natural selection cannotproduce evolutionary change. Of course it can. But if weare to properly recognize it, we must be able to recognize thesignature of selection and differentiate it from drift'ssignature (see, e.g., Bamshad and Wooding 2003). Change inevolution is a heterogeneous category.