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Antiquity of Humanity Later Human Evolution: Homo habilis
Homo habilis was first discovered in 1959 in the Olduvai Gorge in Tanzania. • A nearly complete skull of H. habilis was discovered in 1972 at Koobi Fora on the shores of Lake Turkana in Kenya. Its age is estimated at 1.8 million years and its brain capacity at 800 cc. • Other H. habilis remains have since been discovered at Olduvai Gorge. There is considerable variation among the specimens from this era found thus far. • Some anthropologists argue that the variations appear to indicate that several separate species of humans existed and competed at the same time in east Africa; other scientists lump all the individuals together in a single species.
Homo habilis • Homo habilis is the earliest known species of the genus Homo; that is, the first human species. • It existed from approximately 2.5 to 1.6 million years ago in east Africa. • Only a few fossil remains have been discovered so far, but these specimens exhibit a clear trend toward larger brain size. • H. habilis brains are about 30% larger than those of A. africanus.
Homo habilis • Brain size much bigger than Aus. (500-800) • Teeth smaller, thinner enamel, more parabolic dental arcade. • Skulls rounder, less prognathic, jaw muscles reduced. • East and South Africa, same time as robusts. • Handyman, associated with Pebble choppers (more later).
This reconstructed skull was found in 1972 on the shores of Lake Turkana. • Represents the oldest individual human yet discovered.
Homo habilisAge:ca. 1.8 million yearsDate of Discovery:October 1968Location:Olduvai Gorge, Tanzania
Sexual Dimorphism • Males were much larger than females, as shown by the two skulls at far right. • The male is pictured on the left. • Sexual dimorphism in habilis is expressed in significant size differences.
Tool Technology • Oldowan Pebble Choppers • rounded pebbles • portions broken to form sharp edge • flakes used for butchering
These crude hand axes and stone flakes could have been manufactured as needed or as opportunity arose. The fracture lines of stones create a sharp cutting surface capable of butchering fairly large animals. The photo above right shows a modern anthropologist skinning a calf with a stone tool made just as ancient Homo habilis would have done.
Environment • The background of the photo shows the kind of environment in which this earliest-known human species lived--open bush and savannah country in east Africa. • This must must have been a very challenging environment, filled with large predators. ?
Behavior • Meat eating • Home base, food sharing, sexual division of labor. • Archaeological evidence • Animal bones and stone tools at sites (Olduvai) • Hunting or Scavenging?
"Hunting Hypothesis" • One widely held view of human development has held that hunting as an activity was the chief driver of evolutionary change in early humans, as it would have selected for for certain kinds of intelligence, coordination, and aggressive behavior • Was Homo habilis a hunter of large game and a successful competitor with the great predators of Africa--lions, leopards, hyenas? Or was this species an opportunistic taker of small game and a scavenger? • Present evidence cannot answer the question, but a scavenging role seems more likely.
The Homo habilis Debate • It was once thought that the evolution of the genus Homo was an example of anagenesis, the continual and gradual change of one parent species into its daughter species in a linear fashion. • As the fossil record began to expand and more early human fossils were found dating to the period between 2 million and 1 million years ago, some questions as to the validity of this hypothesis were raised.
Below are two fossils, shown to scale. KNM ER 1813 is to the left, and KNM ER 1470 is to the right. Originally, both were assigned to the species Homo habilis, with ER 1470 thought of as male and the smaller ER 1813 a female in a strongly dimorphic species. However, the anatomies of the two skulls differ considerably.
Differences • Note that there is a strong supraorbital torus (horizontal bar of bone above the eye sockets) on 1813, whereas the supraorbital torus of 1470 is slight at best, and does not have the depression behind it that is seen in 1813. • The face of 1470 is longer than 1813's and 1470's upper jaw is square instead of rounded-off. • There is a great discrepancy between the cranial capacities of the two individuals as well. • ER 1470 has a cranial capacity of 775cc, where ER 1813 has a cranial capacity of only 510cc (which is above the australopith average, but well below the accepted 600cc cutoff for Homo)
Debate • One debate in paleoanthropology today is whether or not ER 1470, and several other fossils previously identified as H. habilis, should be grouped into a new species, Homo rudolfensis. • This classification would acknowledge that ER 1470 and the other members of Homo rudolfensis differ more from Homo habilis, sensu stricto ("in the strict sense," meaning: as originally defined), than could possibly be accounted for by variation within a population or between sexes. • This would place two species of the genus Homo in Africa during the same time period in addition to two members of the genus Paranthropus, and, possibly, late surviving members of the species Australopithecus africanus. • Far more complicated than the original neat, linear model.
Homo rudolphensis (KNM-ER 1813) Homo habilis (KNM-ER 1470)
Homo habilis Height1.0 metres Physique Relatively long arms Cranial Volume 500 – 650 Known Date2.0 – 1.6 million years ago Distribution Eastern & S? Africa Skull form Relatively small face; nose developed Jaws/Teeth Thinner jaw; smaller, narrow molars Homo rudolfensis Ca. 1.5 metres Robust cc600 – 800 cc 2.4 – 1.6 million years ago Eastern Africa Larger, flatter face Robust jaw; large narrow molars Differences