THE SUB-SAHARAN ORIGINS OF CERCOPITHECOIDS, HOMINOIDS, HOMININS, AND HUMANS

Evolutionary processes occurring since the Oligocene in Sub-Saharan Africa gave rise to Old World monkeys (cercopithecoids), apes (hominoids), hominins and humans. Recent discoveries that shed new light on these major divergences have upheld canon, overturned assumptions, raised new questions, and even brought some old ideas back to the fore. For example, newly reported specimens from the Rukwa Rift represent the oldest hominoid (ape) on record and oldest cercopithecoid (Old World monkey) on record. These new, sympatric discoveries push the fossil record of hominoid-cercopithecoid divergence back five million years, from the early Miocene of Kenya and Uganda, into the late Oligocene of Tanzania—aligning better with long-held molecular estimates. In another example, the behaviors and ecologies of the earliest fossil hominins, like Ardipithecus, are persistently debated with new analyses. The utility of any particular extant great ape model for the last common ancestor (LCA) of chimpanzees and humans is being seriously questioned, making reconstructions of extinct hominins even more reliant on reconstructions of others. What’s more, the relevance of the earliest fossil hominoids, like Proconsul, for interpreting the earliest fossil hominins has been reintroduced after decades of much disconnect. And further complicating our reconstruction of hominin origins, the chimpanzee-human divergence might be earlier than the current consensus at 6 million years ago. Taking into account extant ape generation lengths and newly calculated mutation rates, the most recent molecular clock estimates put the LCA at 7–8 million years ago and potentially even older. These new dates, if valid, will not only affect our expectations about the rate of evolutionary change since the LCA and the degree to which early hominins retained arboreality, but they will also change our expectations for the climatic and other environmental conditions surrounding this significant evolutionary event over space and time. This overview of the most recent and promising new fossil discoveries from Sub-Saharan Africa, at sites dating from the Oligocene-Present, provides fertile and exciting ground for studies of paleoclimate and biotic evolution.