The striking similarities in appearance between the human genus Homo and our distant ancestors, the genus Australopithecus, is sufficient reason to place us both along with the genus Paranthropus into the same biological family (Hominidae).  All three genera are bipedal and habitually upright in posture.  Humans have been somewhat more efficient at this mode of locomotion.  Like gracile australopithecines, early humans were light in frame and relatively short.  The evolution of larger bodies occurred later in human evolution.  The differences between australopithecines and early humans are most noticeable in the head.  Early humans had somewhat larger brain cases and comparatively smaller faces.

Late gracile australopithecine		Early transitional human

There may have been two species of early transitional humans living in East Africa--Homo rudolfensis and Homo habilis.  The rudolfensis fossils are earlier, dating 2.4-1.9 million years ago, while the habilis remains are 1.9-1.6 million years old.  Rudolfensis apparently was a bit taller and relatively smaller brained.  However, many paleoanthropologists consider the differences to be too slight to warrant a separate species designation.  As a result, they classify them both as a single species--Homo habilis.  That is the approach taken in this tutorial.  

The evolution of the genus Homo and the genus Paranthropus beginning around 2.5 million years ago coincides with the beginning of a prolonged cooling climate trend in East Africa.  It is likely that this significant environmental change was largely responsible for the rapid evolutionary changes among the hominids at that time.

Homo habilis

Early transitional human fossils were discovered in 1960 by Louis and Mary Leakey at Olduvai Gorge in Tanzania.  The Leakeys named them Homo habilis (Latin for "handy or skilled human") because they apparently made stone tools.  Similar fossils were found at East Lake Turkana in Kenya by Richard Leakey's team of fieldworkers that began searching there in 1969.  These latter specimens were named Homo rudolfensis after Lake Rudolf (i.e., the former name for Lake Turkana).

So far, conclusive evidence of Homo habilis has been found only in the Great Rift Valley system of East Africa.  However, their ultimate geographic range may have been somewhat larger.  Early transitional human fossils also have been found in South Africa in the caves at Sterkfontein and Swartkrans in apparent association with australopithecines and/or paranthropoids.  Not all paleoanthropologists agree that these fossils should be considered Homo habilis. 

Early transitional humans had significantly larger brains than the australopithecines.  In fact, it is beginning with them that our ancestors finally had brains bigger than the great apes.

	adult cranial capacity (range in cm3)
chimpanzees	300-500
australopithecines	400-530
early transitional humans	500-750
modern humans	900-2300

As the early human cranium, or brain case, began to enlarge in response to increased brain size, the mouth became smaller.  In comparison to the australopithecines, the early humans had smaller teeth, especially the molars and premolars.  This suggests that they were eating somewhat softer foods.

Information provided by: http://anthro.palomar.edu