HUMAN EVOLUTION
There have been about 20 human and hominid (human-like) fossils found thus far. Every find leads us to reconceptualize possible lineages leading to humans. The following list includes most of these fossils by their estimated date as well as primate precursors to the hominid line.
50 million years ago - the lemur
Flat face, short snout, large eyes set wide apart. Selection against sense of smell for sense of vision, possibly because early primates were tree dwellers (stereoscopic vision).
Next 20 million years sees the branching off of the present day monkey line from that of the great apes and man.
30 million years ago - Aegyptopithecus
Found in the Fayum, in Egypt. Shorter snout than the lemur, teeth are ape-like, larger but still lives in trees, spending part of the time on the ground.
20 million years ago - Proconsul and Dryopithecus.
Brain markedly larger, eyes now fully forward in stereoscopic vision. Could be on a branch line moving toward apes, not man. Teeth demonstrate that he is an ape, since the jaw is locked by the big canines.
14 million years ago - Ramapithecus
Found in Kenya and India, indicating movement and dispersal. Jaw fragments only showing teeth that are level and more human. Great canines are gone, face much flatter. Man or ape?
Gap of 5 to 10 million years - hiding the time when the ape and human lines separated. Now we have begun to find interesting fossils from this period, but it is still too difficult to draw conclusions
Human - Chimp/Gorilla Separation
6-8 million years ago
7 million years ago - Sahelanthropus tchadensis (Toumaí)
Found in Chad, some 2,500 miles from the normal sites in East Africa, suggesting a new site of origin for humanity. Not clear whether this was an ape or human, or really the common ancestor of both. Brow ridges, teeth that look like on a line to humans (larger molars and smaller cannines). No evidence regarding upright posture.
The next two are recent finds that are controversial. Ape or human?
6 million years ago – Orrorin tugenensis (Kenya)
Appears to have walked upright (long femur neck), arms and fingers retain adaptations for climbing, sharp canine teeth.
5.2-5.8 million years ago – Ardipithecus ramidus kadabba
Considered to be a subspecies of ardipithecus ramidus. We have found a toe, teeth, an adult mandible, pieces of a skull, several arm bones, lower-jaw of a child. Could be chimpanzee. May have walked upright.
5 million years ago
Ardipithecus ramidus
(Ethiopia)
4.4 million years ago
Australopithecus anamensis
(Kenya)
4.2-3.9 million years ago
Australopithecus afarensis
(Lucy - Ethiopia)
3.0-3.9 million years
Two branches now appear (speciation). The second, Genus homo, appears somewhat later than the first, the Australopithecines (“Southern Ape from Afar”):
1.Genus Australopithecines - two forms: one lighter, and one a more robust form. Erect but small-brained. [ Modern feet ]
The lighter "gracile" forms, composed of 3-5 species
Australopithecus africanus (Raymond Dart, 1920's)
3.0-2.3 million years ago.
In the Taung baby found by Raymond Dart, foramen magnum is under skull indicating upright posture. Teeth are small and square - indicates an animal foraging with hands, not its mouth. Teeth may also show it was eating raw meat. To get raw meat the animal was probably making tools, pebble-tools, stone choppers, to carve it and hunt.
Australopithecus aethiopicus – 2.6 million years ago.
Australopithecus garhi – 2.5 million years ago. Found with earliest stone tools.
The heavier, more robust forms, which are sometimes placed in a different genus called Paranthropus.
Australopithecus robustus (S. Africa) – 2.0-1.0 million years ago. Generally nuts and tubors, but perhaps eating some meat.
Australopithecus boisei (Leakey, East Africa) – 2.3-1.2 million years ago.
The Australopithecines lived and died entirely in Africa, with 1 or 2 species surviving until perhaps 1 million years ago.
2.Genus Homo
Homo habilis (Leakey, Olduvai Gorge, Tanzania) 1.9-1.8 million years ago.
Homo rudolfensis - a possible variation of homo habilis.
Homo erectus - 1.8 million – 300,000 years ago. The earliest fossil, of "Turkana boy" (Leakey, 1985), is 1.6 million years.
Large brain size - 1,100 c.c. (three quarters of modern human capacity), showing increase in species over time. Upright posture (as early as 3.5 million years ago)
Populations of this species left Africa for Europe, China (Peking Man) and Indonesia (Java Man). Earliest fossil in Indonesia is 1.8 or 1.9 million years old, leading to the idea that humans originated in Indonesia. Appears to be an older line than previously thought (less archeological work has been carried out in south-east Asia than in Africa). The oldest known African Homo erectus is 1.8 million years old - perhaps Homo erectus is more than 2 million years old?
One million years ago Homo erectus lived on the 3 continents of Africa (homo ergaster), Europe (homo antecessor) and Asia (home erectus). Spread out of Africa
730,000 b.p. - first signs of humans in Europe
Homo heidelbergensis – 600,000 – 100,000 years ago. Generalized diet, lived in Africa, Asia, and Europe.
Homo sapiens - 100 thousand years ago
Then between 500,000 and 100,000 years ago we begin finding a highly confusing group of specimens called "archaic Homo sapiens" who lived on all 3 continents, presumably descendants of Homo erectus. In morphology seem to be intermediate between Homo erectus and modern humans. It would seem that Neanderthal is a direct descendent of these archaic Homo sapiens in Europe.
500,000 b.p. evidence that fire was being used.
400,000 b.p. wooden spears
350,000 b.p. most areas of Europe settled.
The debate over Neanderthal Man. Discovered first in 1856 and has been found all over Europe. Lived from 270,000 to 30,000 years ago. Was Neanderthal our direct ancestor or a separate dead-end line competitively replaced by our true ancestors?
Two theories have arisen to explain what happened - the "multiregional view" and the "out of Africa" view.
Multi-regionalist view (Franz Weidenreich - 1940's)
Homo erectus populations on all three continents evolved in parallel - some migration provided gene flow and prevented all three from differentiating into different species. Changes primarily involved increased brain size and decreased jaws and teeth. Neanderthal therefore represents the European version of a late stage in the global trend.
Out of Africa view
Modern human arose out of one isolated group of Homo erectus in Africa, and then spread. The evidence for this view consists of:
The best and oldest remains of fully modern humans are from 100,000 to 125,000 year ago in Africa.
Genetic variability among modern Africans is larger than all other humans, indicating long presence of modern humans there.
Neanderthal therefore represents one among several non-African descendents of Homo erectus that did not transform to modern humans, but died out.
Homo sapiens sapiens - 50 thousand years ago
40-30,000 b.p. - By 30,000 years ago fully modern human types were widespread through out the world. The earliest humans appear to have inhabited a variety of habitats within a belt of tropical and semi-tropical country stretching from Ethiopia to southern Africa. The population was small, thinly spread, living in groups which probably depended mainly on the gathering of nuts, seeds and plants, which they would have supplemented by scavenging dead animals killed by other predators and perhaps the hunting of a few small mammals. This form of subsistence - gathering and hunting - lasted as the human way of life until the development of agriculture about 10,000 years ago.
During this period we see an expansion in the types of tools being used from a previous 6 to over 80 types. Large hand axes, which required minimum time and effort in production are replaced by very thin, parallel-sided blades from the core of the stone. 20,000 b.p. small projectile points being made. Bone, antler and ivory tools.
New tools - required more complicated manufacturing techniques such as heat treatment and pressure flaking from core of stone. This implies higher motor abilities and greater mental skills that could handle a several stage fabrication process.
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