Fossil skull find might re-write history of human evolution

A pair of fossils recently discovered in Kenya could possibly re-write the history of human evolution.

Washington, Aug 9 : A pair of fossils recently discovered in Kenya could possibly re-write the history of human evolution.

Traditional evolutionary theories of the genus Homo suggest a successive progression: Homo habilis gave rise to Homo erectus, which then evolved into modern humans, the Homo sapiens.

Homo erectus is commonly seen as the most similar ancestor to modern humans, differing mostly by having a brain about three-quarters the size.

But the newly found upper jawbone and skull, which come from two separate skeletons, suggest that Homo habilis was not a direct ancestor of modern humans and that Homo erectus was less modern than previously thought.

The mother-daughter duo of Meave and Louise Leakey, who discovered the fossils, said the jawbone belonged to a Homo habilis dated 1.44 million years ago - meaning that it was far younger than previously known Homo habilis fossils and dated to well after the emergence of the Homo erectus.

Study lead author Fred Spoor, a professor of evolutionary anatomy at University College London said the discovery indicated that the two species lived side-by-side for half a million years in eastern Africa.

"I'm very cautious saying this, [but] it has the potential to remove Homo habilis from the direct ancestral line to us modern humans," said Prof. Spoor.

"Instead, H. habilis and H. erectus may have had a sister relationship that originated sometime between two and three million years ago, which is a well-known gap in the fossil record. The two species likely occupied different ecological niches, allowing them to co-exist without competing against each other for limited resources," he said.

"A good analogy is the chimps and gorillas. There are a bunch of places in West Africa where both of them live in the same area. But they don't interbreed, they keep to themselves," he added.

The researchers are now of the opinion that modern humans evolved from Homo erectus, perhaps via an intermediate form.

Chris Stringer, who studies human origins at the Natural History Museum in London, said that Homo erectus may still have evolved from Homo habilis, but different adaptations and lifestyles could have allowed some populations to live alongside each other for hundreds of thousands of years.

"One possibility is that the larger and perhaps more mobile erectus species was an active hunter, while habilis scavenged or caught small prey," he said.

The other fossil is an exquisitely preserved skull possibly belonging to a Homo erectus. Dated to 1.55 million years ago, it is the smallest Homo erectus skull found so far.

Study co-author Susan Ant�n, an anthropologist at New York University, said, the find suggested that H. erectus could vary tremendously in size.

"One way of reading that is that there is a lot of size difference between males and females, which would be a lot more sexual dimorphism than we previously thought. If this is sexual dimorphism and a lot of sexual dimorphism, then it's probably telling us something about behaviour that was somewhat less like what we are today," Ant�n said.

Previously, scientists believed Homo erectus was more like modern humans in terms of size difference between males and females.

The findings appear in the August 9 issue of the journal Nature, reports National Geographic.

ANI