August 09, 2007	Thursday	Rajab 24, 1428

PARIS, Aug 8: The discovery of two fossils has challenged the belief that our ancestors Homo erectus evolved from Homo habilis, according to an article in the British magazine Nature due out on Thursday.

The finds, on the eastern bank of Lake Turkana in Kenya, suggested that the two species may in fact have co-existed for some 50,000 years in East Africa.

The team that found the remains was led by mother-daughter team Louise and Meave Leakey of the famed Kenyan anthropological family who have uncovered a host of critical human and hominid remains in east Africa.

One of the fossils was an upper jaw bone of Homo habilis that dated back to 1.44 million years ago. It was nevertheless more recent than any of the previously found fossils of its kind.

The second was a remarkably well preserved skull of Homo erectus, which paradoxically dates back even further, to some 1.55 million years ago.

“What is truly striking about this fossil is its size,” said Fred Spoor of London's University College, and one of the paper's lead authors.

“It's the smallest Homo erectus found anywhere in the world.” The recent discovery of the two fossils has created a stir among academics tracing humankind's roots, as it challenges the presumed evolutionary timeline of the species: Homo habilis to Homo erectus to Homo sapiens.

“Their co-existence makes it unlikely that Homo erectus evolved from Homo habilis,” said Meave Leakey, one of the lead authors of the paper.

“The fact that they stayed separate as individual species for a long time suggests that they had their own ecological niche, thus avoiding direct competition.”Homo habilis is a species of the genus Homo, which is thought to have lived from approximately 2.5 million to 1.8 million years ago.

The name, literally “clothed man” was given because crude stone tools were found near the sites of their remains. They were thought to have been succeeded by the Homo erectus, or upright man, whose remains were first found in Asia. But later their fossilized remains ranging from between 1.8 and one million years old were unearthed in Africa, in Europe as well as in Indonesia, Vietnam, and China.

The Homo erectus is an important hominin because it is believed to have been the first to leave Africa.

The weaker teeth and jawbones of the Homo erectus suggest a food regime including more meat, animal fat and softer food unlike the Homo habilis who largely fed on nuts and tubers

The variation in the skull size of the East African Homo erectus fossils — from the petite new skull to a large specimen previously discovered in neighbouring Tanzania — points to sexual dimorphism, or the systematic difference in form between individuals of different sex in the same species.

“In gorillas, males are much larger than females and this sexual dimorphism is related to their strategy of having multiple mates,” said co-author Susan Anton.

“The new Kenyan fossil suggests that contrary to common belief, this may have been true of Homo erectus as well.” The authors point out that like gorillas and chimpanzees, who currently cohabit in Africa without entering into conflict, the two genus species had likely lived side by side on the continent for nearly half a million years.—AFP