Origins of the human race
The earliest ancestors of humankind are known as Australopithecines - commonly known as 'ape men'.
Since 1925 there have been numerous finds of Australopithecus fossils in East and Southern Africa, mainly based around the Great Rift Valley - a fracture in the earth's surfaces that runs 3,500 kilometres from the Red Sea to Mozambique. The non-acidic nature of the Rift Valley soil and sediment has made it the ideal environment for the preservation of specimens.
In 1997 an Australopithecus skull and skeleton was found in a cave in Sterkfontein north of Johannesburg. It is thought to be around 3.5 million years old. The bones are likely to be of a hominid, who fell through a shaft and died while trapped underground.
One of the most famous finds was in Ethiopia's Omo Valley in 1974. It was the skeleton, about 40% complete, of a young girl known to the outside world as Lucy and to Ethiopians as Dinqnish - the wonderful or precious one. She was about the same age as Sterkfontein man.
Australopithecus split into several different species. Some developed powerful teeth and jaws and became known as 'robust' while others were more lightly built and dubbed 'gracile'.
Homo habilis was an individual whose larger brain size enabled it to manufacture simple stone tools, usually pebbles which were split and then chipped to give a cutting edge.
Such technology is most clearly on display in the excavations at Olduvai Gorge in Tanzania - one of Africa's most extraordinary geological sites. The gorge cuts through five colourful volcanic layers, each representing a different period in time, ranging from two million to 500 thousand years ago.
With this species, which evolved around 1.5 million years ago, we encounter an ancestor who looked a good deal like a modern human. Homo erectus was taller than Homo habilis, more robust and had a larger brain. They developed tool-making further, producing a characteristic hand axe known as the 'Acheulian'.
Fossils of Australopithecus and Homo habilis have been found only in Africa, but examples of Homo erectus have been found in the Far East and China while the hand axe has been found in Asia and Europe.
The widely held belief is that these other parts of the world were populated by Homo erectus who left Africa.
Homo sapiens: Out of Africa
By the time the most advanced species of modern man, Homo sapiens, had evolved, about 120,000 years ago, there is evidence of rapid population growth around the globe. So how did Homo sapiens spread?
While it is generally accepted that the forerunner to Homo sapiens - Homo erectus - left Africa about 1.5 million years ago to populate other parts of the world, there are two main theories about the spread of Homo sapiens.
The first theory, known as the 'Out of Africa' model, is that Homo sapiens developed first in Africa and then spread around the world between 100 and 200,000 years ago, superseding all other hominid species. The implication of this argument is that all modern people are ultimately of African descent.
The other theory, known as the 'Multi-regional' Model, is that Homo sapiens evolved simultaneously in different parts of the world from original Homo erectus settlers. This means that people in China descended from the Homo erectus population there, while Australians may have descended from the Homo erectus population in South East Asia.
Both theories have their staunch defenders who cite DNA evidence - analysis of the genetic blueprint passed down from generation to generation - to advance their case. Out of Africa theorists, for example, say that most genetic variation in human populations is found in Africa, suggesting that humans have evolved there for the longest period.
Although the debate is far from concluded, it is probably fair to say that the bulk of scientists support the 'Out of Africa' hypothesis and believe that all humans share a common origin.
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