The Origins of Our Species

The latest discovery of a fossil skull in Kenya, more than three million years old, once again demonstrates the complex evolution of humankind. The following article examines the evidence and sees how it fits into the ideas of human origin formulated by Frederick Engels more than 100 years ago.

"There is a grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved." (Charles Darwin, The Origin of the Species, pp. 459-60, Penguin 1985.)

The latest discoveries in paleontology once again reveal the rich and complex evolution of the human species. In March, the magazine 'Nature' reported on a new fossil find in Kenya of a 3.5 million year-old skull. Originally, it was thought that the human linkage had been traced back to an ancestral genus called the Australopithecines (the "Southern Ape"), the most famous remains being 'Lucy', discovered by D.C. Johanson. These proto-humans roamed the savannahs and Rift Valley of Africa more than 3 million years ago, and are closer to modern humans than apes. However, new evidence suggests that the Australopithecus family was not the only hominid species to have existed at this time.

'Nature' describes a new species - Kenanthropus platyops - with a much flatter face than any Australopithecine. "Kenyanthropus shows persuasively that at least two lineages existed as far back as 3.5m years," said Meave Leakey of the Kenya national museum. It is clear that the evolutionary tree is far bushier that at first appeared. While the human lineage split from that of the African apes some 5-10 million years ago, this new evidence suggests possible new lines from which humans evolved. It shows a far greater diversification of human evolution prior to the emergence of the Homo genus.

The newly discovered skull has a small ear hole, like those of chimpanzees. However, it shares other features of early hominids, such as a small brain. But there are other striking differences, including tall cheekbones, small teeth and a flat plane beneath its nose bone, giving it a flat face appearance. The flatter face - a feature once thought distinctly human - arises primarily from the way the new species ate its food.

"It seems that between 3.5 and two million years ago there were several human-like species, which were well adapted to life in different environments, although in ways that we have yet to appreciate fully", stated Dr Daniel Lieberman, an anthropologist at George Washington University, Washington.

It is understood that, as with the Australopithecus, the Kenyanthropus also walked upright. The emergence of these bipedal apes was a revolutionary breakthrough in human evolution. What forced these creatures in this direction is likely to have been the climatic changes that swept through the African continent some fifteen million years ago. The transformed geography, driven by the separation of two tectonic plates, running from the Red Sea in the north through Mozambique in the south, saw faulting and uplifting of mountains and the creation of the Great Rift Valley. This transformation caused the forests to shrink and fragment, creating radical changes to the habitat of the ape populations.

"The land to the east of the valley was no place for apes, with its forests rapidly disappearing as rainfall levels diminished", states Richard Leakey and Roger Lewin. "One very persuasive theory for the origin of bipedalism, the feature that established the human family, is that it was an adaptation for more efficient locomotion between widely distributed food sources. There are other theories, too, but this one makes good biological sense, given the habitat changes of the time." (The Sixth Extinction, p.88.)

Over a period of several million years, new species arose and others became extinct. The development of hominids with small brains and the ability to walk on two feet represented a qualitative evolutionary leap. In the fossilized riverbed in Laetoli in Northern Tanzania are hominid footprints dated at 3.5 and 3.7 million years. In the words of Leakey and Hay: "the Pliocene hominids at Laetoli have achieved a fully upright, bipedal and free striding gait, a major event in the evolution of man which freed the hands for tool-making and eventually led to more sophisticated human activities. Moreover, evidence supplied by cranial parts of the somewhat later but related hominid fossils from the Afar in Ethiopia (dated between 2.6 and 3 million years) indicates that bipedalism outstripped enlargement of the brain. To have resolved this issue is an important step in the study of human evolution, as it has