Were H. habilis and A. sediba Friends with Benefits? New Findings Complicate the Dawn of Humanity

Perhaps resistance to evolution is just a widespread case of being embarrassed by our parents. In a series of papers released today, paleontologists made a case that humanity descended from a species called Australopithecus sediba – a South African hominid that lived close to 2 million years ago, had small brains, long, tree-climbing arms, and short stature. The males stood about 4'6" and the females were just around 3'0".

But they had great hands with long, graceful looking fingers. "These were tool making hands," said anthropologist John Hawks of the University of Wisconsin.

The papers, presented in the journal Science, give the most complete description of a set of a. Sediba fossils found in 2008, which include remains from five different individuals. Hawks was not an author of the paper but he's been out to the site, and to him, the fossils emerging could finally help us piece together when and how we became human.

Generally, anthropologists consider humanity to include not just Homo sapiens, but other relatives within the larger grouping of homo - including our probably ancestor Homo erectus, as well as the earlier Homo habilis and several others. Three general criteria distinguish these species as human: tool use, large brains and large bodies.

1.8 million year old Homo habilis has been considered the earliest species of human. To put that in perspective, humans branched off from chimps at around 7 million years, and the famous upright-walking small-brained hominid known as Lucy (Australopithecus afarensis) lived 3.2 million years ago. The first stone tools appear to be invented around 2.6 million years ago.

Between our split with chimps and the emergence of the first members of the homo club, however, our family tree gets rather bushy, with various types of Australopithecus living around Africa. What we've been missing, said Hawks, is one that shows a clear ancestral relationships to us.

These newer fossil creatures – Australopithecus sediba – could be those ancestors, but they had some strange features that don't quite fit.

Australopithecus sediba almost certainly had the tool use down, said Hawks. Tools were found around the site, and while it's hard to prove a. Sediba made them, it seems likely, since these hominids had hands that would have been good with tools. And yet a. Sediba was nowhere near human in the size and brainpower departments. Homo habilis, whose name means handy man, ironically had less humanlike hands, though it was taller and its brain was one and a half times the size of the smartest Australopithecus. H.habilis remains are also clearly associated with stone tools.

According to the Science papers, A. sediba had a hodgepodge of other humanlike traits. The skull shape suggests that while the brain was small, it had become rearranged to a more humanlike structure, with more space devoted to the planning and judgment centers of the frontal cortex.

The ankle is humanlike and the heel is chimplike. The pelvis was also very humanlike, which is weird, said Hawks, because we thought our pelvis shape evolved to make it possible for women to give birth to babies with bigger brains, and yet the brain of a. Sediba is small.

So far, anthropologists are split over whether they think the ancestor to all humans is A. Sediba or homo habilis. Maybe it's both – our search for a single common ancestor foiled by the sexual antics of a variety of species. It's worth considering, said Hawks, since DNA evidence has shown anatomically modern humans mated with Neanderthals. Just last week new research was published showing evidence that early modern humans interbred with so-called archaic humans living in Africa.

This sort of thing happens. Other mammals can interbreed when separated by less than a million years of evolution, said Hawks, so in the same vein we may have inherited our hands from one species and our heads from another.