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With an unknown amount of evidence yet to be found and possible bias in our interpretations, current accounts of human evolution can only be provisional.
People often enjoy reading about where humans come from and how we developed into the unusual creatures we are today: upright-walking, omnivorous mammals who inhabit every continent (and who enjoy reading about our own evolution). Such accounts generally offer a presentation of the fossil evidence for human evolution and a narrative describing how we gradually transformed from our apelike ancestors, via a series of intermediate forms, into modern humans. Popular narratives on this topic generally include explanations about how, when, and why our human ancestors' posture became upright, their gait became bipedal, their diet shifted from vegetarian to a combination of meat and plants, and their brains enlarged.
Unfortunately, we have to disappoint you. Although a narrative of this type would look like an accurate account of human evolution, it would almost certainly differ from the real evolutionary history. Instead, this article will lay out our reasons for thinking the existing human fossil record is incomplete in almost all respects, with little chance that any narrative explanation offered today can be the right one. If the human evolutionary story were a play or a novel, many of its characters would be absent, misrepresented, or poorly developed, and the plot would have many holes.
Indeed, we do not yet have all the evidence needed to generate an accurate narrative of human evolution. Why then do paleoanthropologists routinely present our current understanding as if it were authoritative? We suggest that it is a profoundly human trait to want a straightforward and complete story. We have all grown up with oral and written narratives, just as our ancestors did for tens, maybe even hundreds, of thousands of years, and nearly all these stories follow a full narrative arc. We know who the main characters were, we know how the story started out, and we know how it ended. We expect the story of our evolution to follow the same arc.
A straightforward account is elusive, however, because of two factors that inevitably complicate any attempt to reconstruct evolutionary history: what is missing from the fossil and archeological record, and the great variety...