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

Abstract

Humans are lucky to have two closest relatives and not just one. While chimpanzees have been the focus of far more research and are thought to more closely represent our last common ape ancestor, the bonobo will be as important as the chimpanzee in reconstructing our past. Understanding human evolution requires not only knowing what traits are derived but also identifying what process may have shaped these traits as they evolved. We suggest in this paper that while chimpanzees may be best suited to help identify derived traits, bonobos will be crucial to testing ideas regarding how selection shaped the human lineage. We base our argument on the self-domestication hypothesis that has generated a host of recent studies comparing the development of morphology, physiology, behavior and cognition in bonobos and chimpanzees. "If the deduction that the bonobo is highly derived with respect to the other chimpanzees is correct, then its similarities to humans become even more significant: the original human environment has long been exceeded, but we may suppose that bonobos still occupy the niche to which they are best adapted. Thus by examining this niche we may learn something about the early human niche, or at least aspects of it."

Oxytocin and vasotocin receptor variation sheds light into the evolution of human prosociality

“…Our results could be used as a springboard for other studies delving into the differences in prosociality between bonobos and chimpanzees, as well as for those studies looking into evidence for convergent evolution in bonobos and modern humans in an attempt to explain their similarities in terms of prosocialit 107, 108 . We found three alleles that bonobos and modern humans share (rs237897(A), rs2228485(G) and rs1042615(A)), while we did not find any for modern humans and chimpanzees.…”

Self-Domestication Hypothesis

“…Bonobos, pan paniscus, are a good animal model to assess self-domestication since more precise comparisons can be made to its undomesticated great ape sister, the chimpanzee, Pan troglodytes. Evidence indicates that bonobos speciated from chimpanzees due at least in part to allopatric speciation as a result of the physical barrier of the Congo River, where there is little genetic admixture between the bonobos south of the river and chimpanzees north of the river (Hare and Wrangham 2017).…”

“…Chimpanzee societies are organized by dominance hierarchies, which provide a stable albeit somewhat totalitarian social structure that drives many of the incentives for violence (Hare and Wrangham 2017). Dominant chimps bully subordinates and subordinate male chimps bully others below them, who in turn bully female chimps.…”

“…Dominant chimps bully subordinates and subordinate male chimps bully others below them, who in turn bully female chimps. Additionally chimpanzee males often form coalitions of adolescents that attempt to and often successfully aggress against other chimps especially the dominant chimps in an attempt to oust them from power (Hare et al 2012;Hare and Wrangham 2017;Wrangham and Peterson 1996).…”

“…Unlike chimpanzees, bonobos show very little to no aggression towards females, in large part because males do not form coalitions while females do, and they often do so to fight off aggressive males (Hare and Wrangham 2017;Surbeck and Hohmann 2013). Females form the highest ranking members of bonobo society, where no bonobo society has been recorded to have a male or a coalition of males as its highest ranking members (Hare et al 2012;Hare and Wrangham 2017).…”