午夜福利1000集合

A CHALLENGER for the title of oldest human ancestor has emerged from
Ethiopia. The 5.8-million-year-old contender, which weighs in at around the same
size as a modern chimpanzee, threatens to boot the reigning champion, Millennium
Ancestor, down to the lower branches of the evolutionary tree.

The dawn of humankind occurred 5 to 7 million years ago, when the ancestors
of apes and humans went their separate evolutionary ways. But the fossil record
of this split is scarce.

Last year, scientists in Kenya announced they had found the earliest
human-like animal, Orrorin tugenensis, which they dubbed Millennium Ancestor
(New Scientist, 16 December 2000, p 5).
They believe the creature had
human-like features and walked upright some 6 million years ago. But
palaeoanthropologists have questioned whether Orrorin is a true hominid.

Now Yohannes Haile-Selassie of the University of California at Berkeley says
he has discovered a hominid that lived between 5.2 and 5.8 million years ago in
the Horn of Africa. Bones and teeth from five individuals are similar in shape
and size to the previous oldest-known hominid, the 4.4-million-year old
Ardipithecus ramidus. But the new find has sharper canine teeth than later
hominids, suggesting it is a more primitive subspecies of A. ramidus.
鈥淲e are looking at some kind of transitional form, and for me that is highly
significant,鈥� says Haile-Selassie.

Crucially, the shape of a toe bone shows that the new creature walked
upright鈥攁 defining feature of the human line, says Haile-Selassie. The
hominid has been dubbed Ardipithecus ramidus kadabba, 鈥渒adabba鈥� meaning
鈥渂asal family ancestor鈥� in the Afar language.

Haile-Selassie says we need to find more specimens of Orrorin before
we will know for sure if it could walk upright, and he suspects it may be a
common ancestor of chimps and humans. It might even turn out to be an
evolutionary dead end.