 Charles Darwin pioneered an approach to the study of instinct that aimed to show, above all, that instincts evolve gradually as adaptations to a species’ environment. Darwin’s theory of instinct was developed in opposition to William Paley, William Kirby, and other influential Natural Theologians (Grinnell 1985; Richards 1981; 1987; Rochowiak 1988). Paley defined an instinct as “a [behavioral] propensity prior to experience and independent of instruction” (Richards 1981). Examples such as bird migration, nest building, and mating preference seemed, to Paley, not possibly acquired by experience. The best explanation for these instincts was that they are Divinely implanted. Likewise, Kirby viewed animal instincts as a means by which God animates the material world: “if animals lost their instincts, birds would no longer build their nests, or migrate, or learn to fly. Bears would not know when to hibernate, nor salmon when to be driven upstream to spawn; the entire animal kingdom would be thrown into disarray” (Grinnell 1985, 57). Like many theologically inspired naturalists at the time, Paley and Kirby drew a sharp distinction between instinctive vs acquired behavior. Since instincts were thought to be designed by God, and thus perfect, there would be no need to supplement or modify them through individual learning.