THE QUEST FOR HUMAN ORIGINS

The search for the earliest human ancestors has been an area of science very much dominated by individuals, often with strongly held views about the interpretation of their finds. The story of the discoverers tells much about the history of the subject.

Not surprisingly, many of the earlier finds were made in heavily populated Europe, with several discoveries in the 19th-c of evidence of early habitation in caves. In 1863 discovered the first evidence that man had lived in Europe during the last ice age and soon afterwards found several skeletons of Cro-Magnon Man, the earliest human predecessor found in Europe. although a relatively recent ancestor in evolutionary terms.

The publication of ideas on evolution in 1858 led to a conscious search for a ‘missing link’ between humans and the apes, and in 1891 discovered fragments of Homo erectus (Java Man), a hominid that walked upright about 0.5–1.5 million years ago. Like many after him, Dubois’s interpretation of his finds was widely ridiculed at the time, but accepted later after Otto Zdansky found other examples of Homo erectus near Peking in 1926. So strongly was opinion divided about Darwin’s theory and the nature of human ancestry that some were tempted to fabricate evidence, such as the ‘discovery’ in 1912 of Piltdown Man, widely accepted as one of our early ancestors until conclusively shown to be a fake in 1953.

It is commonly accepted today that the human family, the Hominidae, originated in Africa from ape-like ancestors, whence they migrated across the globe. This Out of Africa theory is reflected by the subsequent pattern of hominid discoveries. In 1924 had announced the discovery of a hominid twice as old as Java Man; Australopithecus africanus , from Taung, Botswana, was 1.2–2.5 million years old. The ‘Taung baby’ was the first truly primitive ancestor within the human family to be found; soon afterwards found a second example at Sterkfontein, followed in 1938 by the first specimen of Australopithecus robustus (1–2 million years old).

In 1960, in the Olduvai Gorge in East Africa found Homo habilis , a large-brained hominid that made and used tools.

A major step back in time was achieved in 1974 when discovered ‘Lucy’, a female Australopithecus afarensis about 3.1 million years old, in the Afar valley of north-eastern Ethiopia. Tantalizingly, 2 years later discovered the footprints, but no remains, of a hominid walking upright at Laetoli on volcanic ash dated as 3.75 million years old.

The oldest hominid currently known is 4.4 million years old and again hails from the Afar valley. Australopithecus ramidus was found in1994 by a Japanese/American/Ethiopian team; far from being a complete skeleton, the remains consist of 50 fragments of bone and teeth from a group of 17–20 individuals, including jaw and skull fragments and a complete left arm. Predating the use of stone tools by almost 2 million years, A. ramidus lived in a woodland area also inhabited by monkeys, antelopes, sabre-toothed cats, rhinos and elephants, and was probably predominantly vegetarian. Although these hominids walked upright like humans, it is thought that they would have slept in trees, and resembled apes in other ways.

Human skeletal remains dated as being between 500 000 and 300 000 years old appear to be the earliest (‘archaic’) examples of Homo sapiens. Debate continues on whether he was contemporary with, or a successor to, late populations of H. erectus.

The classification of these finds, and the interpretation of their interrelationships and migrations, can be assisted by DNA analysis. In 1995, DNA studies at Yale on part of the Y chromosome of 38 living men from around the world showed the samples to be surprisingly similar. The simplest explanation for this lack of ‘genetic scrambling’ is that modern humans are genetically young, ie only a few hundred thousand years old, and that they developed from a single homogeneous colony and not from separated and scattered centres. Mitochondrial DNA studies show that African, Asian and European populations probably shared a common ancestry more than 100 000 years ago, but division (following the Out of Africa movements) occurred some 40 000 years ago so that Asian and European populations are biochemically closer to one another than either now is to any African population.

Current thinking, on the basis of both fossil finds and genetic evidence from modern human and ape populations, suggests that the split between humans and apes occurred some time between 5 and 8 million years ago and that hominids who could merge in a human crowd today without much difficulty first appeared not more than 100 000 years ago. But although these ancestors of 100 000 years ago had language and social awareness, it seems (judging by their cave art) that another 50 000 years passed before religious and supernatural belief systems appeared.

We are not descended from apes, but we and they are linked to an earlier ancestral species: they are cousins and not forefathers. Modern humans ( Homo sapiens ), able to speak, are in evolutionary terms successful, but to a catastrophic extent: our numbers are 6 billion (the UN figure for October 1999) and seem set for continual increase.