A cue for adaptive explanations was suggested by Darwin himself (Darwin, 1871), who, in a statement strikingly and diversely germane to the topic discussed herein, considered “liability to the same diseases . . . our tastes in common for the same stimulants, and the similar effects produced by them, as well as by various drugs” (vol. 1, p. 191) as a major evidence for common evolutionary origin of humans and other “higher mammals” (he fittingly listed taste for tea, coffee, “spirituous liquors” and tobacco smoking in monkeys [p. 12]). Lacking the ability to directly observe the process of evolutionary change, we can, following Darwin, rely on evolutionary stability, commonality of characteristics between humans and other species. Similarity of the structure of extremities between vertebrates or “our close similarity in minute structure and chemical composition” (Darwin, 1871, vol. 1, p. 191) with other mammals indicate both common origin and subsequent evolutionary divergence. Likewise, tracking behavioral characteristics, particularly those pertaining to addiction, to their common origin supports the evolutionary scheme.
