Fossil could rewrite human evolution

The discovery of a nearly-complete early human skeleton is set to revolutionise scientists' understanding of human evolution.

Homo habilis lived 2.0-1.6 million years ago and had a wide distribution in Africa

While there have been thousands of fossilised fragments from human ancestors unearthed around the world, the story of mankind's progression from simple primates to modern, intelligent humans is far from complete.

The fossil record, which spans millions of years, contains large gaps while in some cases entire species have been described from just a few small pieces of bone.

Some religiously-inspired opponents of evolution theory use the patchy fossil record to argue that humans did not evolve from primates.

But rare fossil finds like the new skeleton from the Malapa caves in Sterkfontein, South Africa, give anthropologists the opportunity to gain huge insights into how our prehistoric ancestors lived and looked.

Africa is now widely accepted as the birthplace of mankind as simple primates evolved into the common ancestor we share with the great apes such as Chimpanzees and Gorillas.

Around 3.9 million years ago a species known as Australopithecus afarenus emerged, which was apelike but also shared certain characteristics with modern humans like the ability to walk upright on two legs.

This bipedalism, however, has remained one of the most contentious issues in human evolution and the evidence for exactly when human ancestors moved onto two feet to walk around remains a hotly debated subject.

The first truly human-like species is thought to have first appeared around 2.5 million years ago in southern and eastern Africa.

Homo habilis, as it has been named, had a 50% larger brain capacity than its predecessors and was the earliest species to be placed by scientists in the genus Homo due to its human-like characteristics.

This larger brain is believed to have given the species an edge that its more apelike ancestors had not benefited from, allowing it to begin to form more complex social groups and to master the use of stone tools.

Despite this growing intelligence, however, Homo habilis is not thought to have shared the sophisticated hunting abilities of its descendants, Homo erectus and later Homo sapiens, that would come to dominate the planet.

There is some evidence they were in fact a staple in the diet of large predators such as Dinofelis, a large scimitar-toothed predatory cat.

But the description of Homo habilis is based on just a few key fossils. The first, which was used to define the species, consisted of a lower jaw found in Tanzania along two fragments of skull and 21 finger, hand and wrist bones.

Another fossil, found in 1973 in Koobi Forea, Kenya, is the most complete Homo habilis cranium found so far. No examples of a pelvis or complete limbs have been discovered.

With so few fossils, scientists have struggled to draw a definitive timeline of how human species evolved and arguments about how individual fossils should be ranked are common.

Experts will be keen to pour over the new fossilised hominid after it is unveiled this week in a bid to unravel more about what its place should be. The team who discovered it will certainly face counter claims about where exactly in the evolutionary tree it should sit.

With an almost-complete skeleton, however, it will be possible to determine whether this early ancestor of humans climbed trees or lived on open grassland and if it stood upright or used its arms to assist when walking.

Armed with this kind of detail, scientists should be able to make far more conclusive statements about how our own species evolved.