To model or not to model? A recent search of the internet using three key words, “chimpanzees model humans,” yielded 27,200,200 pages of results, in less than half a second. Recently, chimpanzees (Pan troglodytes) have been labeled as unsatisfactory models in understanding human evolution (Sayers and Lovejoy 2008; White et al. 2009). Highlighted differences between the anatomy of Ardipithecus ramidus (a hominin species living in East Africa at 4.4 Ma) and of the extant African apes suggest that the last common ancestor (LCA) of humans and African apes was morphologically more primitive than previously assumed (Pilbeam and Young 2004). This suggests that several primitive traits common to extant African apes and early hominins might have been a result of convergent adaptations rather than phylogeny (Stern and Orgogozo 2009). The reconstructed paleobiology of Ardi emphasizes behavioral (e.g., facultative bipedality) and morphological (e.g., reduced canine teeth) divergences from the extant chimpanzee. According to Lovejoy et al. (2010, p. 410), these conclusions “were based on intensive review of homologous traits in other primates,” using a method known as strategic modeling (cf. Whiten et al. 2010). The aim of our paper is not to seek to prove that the chimpanzee is the best or only model for human evolution, compared with other living nonhuman species. Nor do we argue about the implications of vague behavioral terms, such as facultative bipedalism (e.g., how much bipedal locomotion does a facultative bipedal perform?), or broadly omnivorous (e.g., how much fruit needs to be in the diet for a species to be classed as a ripe fruit specialist, given that diets vary considerably with ecological context?), or terrestrial and arboreal feeder (e.g., what percentage of food must come from the ground versus above it?). Chimpanzees are insufficient models, if they are presented as the only useful species for reconstructing the hominin fossil record, nor are they time machines, whereby chimpanzee behavior precisely mimics LCA or hominin behavior. As we share various features with all primates (Fleagle 1998; Martin 1990), different research topics are better approached with a comparative approach, using pertinent species as models. Research that uses comparative primate modeling covers a wide range of human behavioral patterns, from tool use to contagious disease (Boyd and Silk 2009; Chapman et al. 2005).
