Equal, Similar, but Different: Convergent Bonobos and Conserved Chimpanzees

Abstract

A critical goal for human evolutionary biology is understanding when and how traits evolved in our ancestral lineage during the 6.5-9.3 million years since our split with the ancestors of chimpanzees and bonobos. Comparisons among humans and living apes are essential as they allow us to discriminate between traits that we share through common descent and those that have been modified since our split from Pan. This chapter suggests, based on the most recent quantitative comparisons of behavior, physiology, development, and cognition, that in many respects chimpanzees most closely approximate our last common ancestor (LCA) with chimpanzees and bonobos. It also suggests that bonobo and human psychology are similar in ways that indicate that cognitive evolution in the two species was guided by parallel mechanisms. The chapter discusses three main hypotheses: mosaic hypothesis, bonobo-like hypothesis, and chimpanzee-like hypothesis. The mosaic hypothesis claims that the relationship between traits in the living apes is not sufficiently consistent to suggest that one species is more representative of the LCA. The bonobo-like hypothesis has been suggested based partly on qualitative comparisons of behavior and cognition. The chimpanzee-like hypothesis conforms to evidence that bonobos are highly derived phenotypically relative to other nonhuman apes.