A cranium found in 1972 and the lower jaw of a newly discovered fossil,
shown reconstructed and combined above, are believed to be from
the same ancient hominid species.
The big-brained, upright primates of the genus Homo—the group to which we modern-day humans belong—evolved in East Africa around 2.4 million years ago. By half a million years later, Homo erectus, from whom we’re directly descended, was walking the plains near Lake Turkana in what is now Kenya. But anthropologists have increasingly come to believe that Homo erectus wasn’t the only hominid around. Three newly discovered fossils, detailed online this week in Nature, confirm that at least two other Homo species lived nearby—providing the strongest evidence yet that several evolutionary lineages split off in the genus’s early days.
In 1972, researchers found a partial skull in the fossil beds near Lake Turkana. Its big cranium—with room for a large brain—made clear it was a member of the genus Homo. Its unusual face, flat and long, led some scientists to believe it represented a new species, dubbed H. rudolfensis; others felt the skull could just be an odd-looking specimen of a known species, H. erectus or H. habilis, an example of natural variation in action. With the skull’s entire lower jaw missing, it was impossible to make a definitive classification.
Just a few years ago, researchers found fossils of a complete and partial lower jaw and of another face, dating from 1.78 million to 1.95 million years ago. The newly discovered jaws fit well with the earlier skull, as shown above, and are different from those seen in before, confirming that the 1972 find is a new species. The other find, the fossil face, was from a juvenile, and clearly mirrored the other skull’s features and shape. (The researchers aren’t naming which species is which, exactly, until the fossils are dated and compared to existing specimens; Erin Wayman at Smithsonian’s Hominid Hunting blog delves into the full explanation of why.)
These new discoveries bolster the idea that the human family tree wasn’t, as scientists once thought, a steady climb upward; even within our own genus, life was branching out in several directions. As anthropologist Ian Tattersall told the New York Times, “it supports the view that the early history of Homo involved vigorous experimentation with the biological and behavioral potential of the new genus, instead of a slow process of refinement in a central lineage.”