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First detailed anatomical study of bonobos exposes bonobos as best model for human‐chimp ancestor and just‐so stories of human evolution, bipedalism and tool use

Just‐so stories are prominent in human evolution literature because of our tendency to create simple progressionist narratives about our ‘special’ place in nature, despite the fact that these stories are almost exclusively based on hard tissue data. How can we be so certain about the evolution of human facial communication, bipedalism, tool use, or speech without detailed knowledge of the internal anatomy of, for instance, one of the two extant species more closely related to us, the bonobos? Here I show how many of these stories now become obsolete, after such a comprehensive knowledge on the anatomy of bonobos and other primates is finally put together. Specifically, each and every muscle that has been long accepted to be ‘uniquely human’ and to provide ‘crucial singular functional adaptations' for our bipedalism, tool use and/or vocal/facial communication, is actually present as a variant or even as normal phenotype in bonobos and/or other apes. Importantly, chimps and in particular bonobos also provide a remarkable case of evolutionary stasis: within >120 head‐neck (HN) and forelimb (FL) muscles, since the chimp‐human split c.8Mya there were only four minor changes in the chimp clade, and all were reversions to the ancestral condition. Outstandingly, since the common chimp‐bonobo split c.2 Mya not even a single change occurred in bonobos, i.e. regarding the HN‐FL musculature bonobos are the best living model for the common chimp‐bonobo LCA and the chimp‐human LCA. The extremely static Pan evolution becomes even clearer when hindlimb data are added: only two muscle absence/presence differences occur between common chimps‐bonobos, and none of these species has muscles not found in other primates. Puzzlingly, there is an evolutionary mosaicism between each of these species and humans. I discuss these data in the context of available genomic information and debates on whether the common chimp‐bonobo divergence is linked to heterochrony, and put these data together with that available for humans and other other primates in order to provide a more comprehensive, and less biased, understanding of primate and human anatomical evolution.