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The missing link: 5 million years ago?

Exactly where and when the genealogy of mankind branches off from that of the apes has been a matter of detailed controversy ever since the Darwinian 'missing link' was first sought. We still do not know even the approximate date, though some scientists now believe that it was not much more than 5 million years ago.

The evidence of DNA demonstrates that the place was almost certainly Africa. Comparing human DNA with that of the apes, it has been shown that the African pair of apes are more nearly related to us than the two from Asia; and of the African primates, the chimpanzee is a considerably closer cousin than the gorilla. We share 98% of our genes with chimpanzees.

From a period about 4 million years ago there begin to be fossils of creatures as close in kind to human beings as to apes. It is a measure of their intermediate status that they have been classed as hominids (hominidae man-like) but have been given the species name Australopithecus ('southern ape').

Australopithecus is a confusing name with its hint of Australia ('southern land'), but these ape-men are southerners in a different sense. Their remains have been found in the southern hemisphere, and specifically in southern and eastern Africa.

Several varieties of Australopithecus seem to have coexisted in Africa over a span of more than 3 million years. What they have in common with each other, and with us, is a preference for walking upright on two feet. They may also have used sticks and stones to fight, for they have less dangerous teeth than their ape ancestors.

With them and their immediate predecessors, something more than 4 million years ago, our own era can at last be said to be dawning. And we are already 99.95% of the way through the story.

Lucy: 3 million years ago

Until recently the first known individual with partially human characteristics was a little Australopithecus female called Lucy (given that name some 3 million years after her death, because the Beatles hit Lucy in the Sky with Diamonds was on the radio at the time of her discovery). Lucy's almost complete fossilized skeleton was found in Ethiopia, in the Awash valley, in 1974. Although fully grown, she was only about 107cm (3'6') tall. .

In 1992-3 a new group of fossils began to be unearthed, less than 50 miles from where Lucy was discovered. By 1994 they included the complete skeleton of a female now nicknamed Ardi, short for the name given to the new species, Ardipithecus Ramidus. The fossils have been dated, by their position between two layers of volcanic strata, to about 4.4 million years ago, more than a million years before Lucy. So Ardi is at present the earliest skeleton of a creature with sufficient human characteristics to be very possibly our direct ancestor.

Fossils of Lucy’s kind are numerous, spanning the period 4 million to 1.5 million years ago. There is much academic debate as to how the fossils relate to each other, and how many different species of Australopithecus there are. But it is certain that they, like the much earlier Ardipithecus, are all intermediate between apes and men, not only in their relatively upright posture but also in their habits.

Apes move with greater ease in the trees than on the ground. Ardipithecus lived exclusively in the forest and was perhaps equally at ease in the trees or on the ground. Lucy and her kind prefer the ground and therefore can extend their range from wooded districts to the plains. Even so, Lucy's long arms and short legs suggest that she still finds movement in the trees an easy option

About a million years after Lucy (or some 2 million years ago) there begin to appear fossils of creatures so much closer to us that they have been specifically classed as human, sharing with modern people the genus Homo.

The earliest known type of human has been called Homo habilis ('handy man') because simple tools, made from flakes of stone, are regularly found with his remains (fossil bones of this kind were first identified at Olduvai Gorge in Tanzania in 1959, but are now known from several other African sites).

As with Australopithecus, there is much dispute as to how many varieties of Homo habilis there are. Surviving specimens range in size from as small as Lucy to almost the height of modern humans.

What is certain is that for about a million years Lucy and her kind coexist in Africa with creatures more recognizably human.

Homo erectus: 2 million years ago

One human variety, first appearing about 2 million years ago, has provided a fossil skeleton even more complete than Lucy's.

It is of a boy, about eleven years old and not yet fully grown, who once stood slim and upright with a height of about 1.62m (5'4'). His fossil, discovered in Kenya in 1985, has been dated to about 1.6 million years ago - some 400,000 years after the earliest known remains of his species.

Humans of this kind have been named Homo erectus ('upright man'). With them we reach the first creatures to be undeniably our ancestors and ours alone.

Argument will long continue as to which of the earlier species of Homo habilis (and before them of Australopithecus) are the link between us and the origins of life. But there is little doubt about Homo erectus, because by about a million years ago he is the only surviving hominid. All other man-like creatures have died out -- presumably because they find it impossible to compete for the necessities which they (but not the apes) require in common with Homo erectus.