Early Homo: Homo Habilis
(2.5 million to 2.0 million years ago)
Louis and Mary Leakey were the first hominid that was classified as early Homo–at Olduvia George in Tanzania in 1960. They named their fragmentary discovery Homo habilis, “Handy Person,” a label that commemorated the assumed toolmaker abilities of these hominids. Then Richard Leakey found the famous Skull 1470 in East Turkana, a large–brain, round–headed cranium that confirmed the existence of Homo Habilis.
If you had encountered Homo Habilis 2 million years ago, you would have seen little to distinguish the new hominid from Australopithecus. Both were of similar height and weight about 4 feet 3 inches tall and 88 pounds. They were bipedal, but Homo Habilis would have looked less apelike around the face and skull. The head was higher and rounder, the face less protruding, the jaw specialized teeth. The molars were narrower; the premolars smaller; and the incisors larger and more spadelike, as if they used for slicing. However, microscopic wear studies of the teeth show that both Australopithecus and Homo Habilis were predominantly fruit eaters, so there does not seen to have been a major shift in diet between the two. Homo Habilis had a larger brain, with a larger cranial capacity between 600 and 700 cubic meters, in contrast with those of Australopithecines, which ranged between 400 and 500 cubic centimeters.
Thigh and limb bones from Koobi Fora and from Olduvia confirm that H. Habilis, walked upright. The hand bones are somewhat more curved and robust that those of modern humans. This was a powerful grasping hand, more like that of chimpanzees and gorillas than of humans, a hand ideal foe climbing trees. An opposable thumb allowed both powerful gripping and the precise manipulation of fine objects. With the latter capacity, H Habilis could have made complex tools. There was probably considerable difference in size between males and females.
Habilis skeletal anatomy gives a mosaic picture of both primitive and more advanced features, of a hominid that both walked bipedally and retained the generalized hominid ability to climb tress. A telling clue comes from one of the Olduvai's specimen's upper arm bones, which, like Lucy, are within 95 percent of the length of the thigh bone. The chimpanzees has upper arm and upper leg bones of almost equal length, whereas modern humans upper arms are only 70 percent of the length of the upper leg bones. Almost certainly H. Habilis spent a great deal of time climbing trees, an adaptation that would make them much less human in their behavior, and presumably in their social structure, than had been assumed even a few years ago.
Homo Habilis, like many taxonomic labels, accommodates what may actually be two or three more early human species. The resulting proliferation of hominid names reflects a concern with documenting an anatomical variation which far exceeded possible possible differences between males and females. For example, Homo Habilis may have lived alongside another East African form, Homo rudolfensis.
For clarity, we retain the generic term Homo Habilis here but stress that it disguises considerable morphological variation, especially after 2 million years ago, when new humans forms were evolving in Africa and perhaps Asia to.
A Burst of Rapid Change?
Our scientific predecessors thought of evolution as a gradual and progressive mechanism. The early East African fossil suggest a very different scenario, coinciding with that of the current view of evolution as a punctuated equilibrium—long periods of relative stability punctuated with bursts of rapid change caused by new, selective pressures resulting from altered conditions, perhaps environmental change or alterations in the organism itself.
Such a burst of rapid change could have taken hold during the brief 500,00 years that separate A. garhi from H. habilis. Whoever was the first toolmaker, the development of stone tool technology gave its inventors a major advantage over other hominid species. Stone hammers and flakes let them to exploit predator kills and shift to an engery—rich, high fat diet, which could lead to all manner of evolutionary consequences. Major anatomical developments occurred during the millennia that separated early Homo (H. Habilis) from Homo erectus, who appeared in East Africa about 1.9 million years ago. Brian size increased from about 450 cubic centimeters in A, afarensis to 1,000 cubic centimeters in H. erectus. There were further modifications in hips and limbs for bipedal locomotion. The primitive body form of earlier hominids vanished only with the emergence of the much more advanced H. erectus. However, what caused this changed of evolutionary pace remains a mystery, although climate change especially cooler temperatures, played a role.
