   These works by Fisher and Wright are canonical contributions to the field of evolutionary biology. They were based partially on prior claims and counterclaims about the influence of natural selection and of non-selective forces on trait evolution, especially in species such as land snails that have easily distinguishable trait variation (see Millstein 2007a). In turn, these works stimulated continuing claims and counterclaims. The mid-1970s explosion of citations reflects the fact that the number of biologists studying ecology and evolution increased markedly as compared to the early 1960s and that evolutionary biology gained separate departmental status at many universities; these changes were in part caused by the increased societal awareness and concern at that time about pollution and the impact of humans on the environment. There were two central but mainly disjunct scientific developments that energized the proliferation and refinement of adaptationist and of pluralist views during this period. The first was the extensive development of “strategic” claims in evolutionary ecology, which in the case of a given trait, say, the allocation of energy to male and to female offspring (e.g., Hamilton 1967; see also Charnov 1982), provides an explanation as to why the observed trait is locally optimal. Such a claim invokes only natural selection as an important causal explanation of the trait. The second development was the neutral theory in population genetics, which posits that natural selection plays little or no role in determining DNA and protein sequence variation in natural populations (e.g., Kimura 1968, 1983). The former development generated little initial controversy, while the latter development immediately generated lasting controversy (see Dietrich 1994).