Science continues to struggle with one of the most basic questions of all: Where did humans come from.
There isn't much question that modern humans came out of Africa, probably in several waves of migration over the past 100,000 years. But it now appears that the ancient ancestors who gave rise to those African humans might have come from Asia.
Until recently the only fossils of anthropoids -- the creatures at the base of the branch of the evolutionary tree that gave rise to primates, including humans -- were found at a place called the Fayum in Egypt. But a growing body of evidence suggests our distant relatives might have developed closer to Cambodia than Cairo.
Just over a month ago, French researchers published a report in the Proceedings of the National Academies of Science, arguing that new analysis of an ankle bone they found a few years ago in Pakistan belonged to a family of anthropoids that predate by millions of years those found in Egypt. Since the 90's, similar fossils have been found in Myanmar, China, and Thailand.
Laurent Marivaux, a French paleontologist who was on the team that found that ankle bone, says emphatically that his interpretation of the fragmentary fossils they found is ''conclusive. They are anthropoids!"
Other anthropologists remain skeptical -- the evidence is far stronger, they say, that early anthropoids evolved in northern Africa. At the Fayum, an incredibly rich multilayered bed of fossils has revealed whole skulls and jaws and teeth and other remains dating back as much as 34 million years that pretty clearly share features with humans, apes, and monkeys, and no other species.
Compared to the evidence found in Egypt, the Asian evidence is ''very incomplete," and less easily interpreted as bearing definite anthropoid characteristics, said John Fleagle, distinguished professor of anatomy at State University of New York at Stony Brook. ''There are hints of anthropoid anatomy in the teeth and the ankle bones of some of the Asian fossils, but the few bits of skull suggest otherwise."
''There isn't much of a consensus in the field today," said Fleagle, also editor of the journal Evolutionary Anthropology. ''There are strong opinions on both sides."
The mammal fossils found in Egypt clearly share features with people, apes, monkeys, and other animals on ''our" branch of the evolutionary tree, said Eric Delson, chairman of the anthropology department at Lehman College of the City University of New York. Those features include eye sockets walled off by bone in the back -- non-anthropoid primates have a bony ridge around the side of their eye socket but no cup in the back; one bone in the front of the skull -- in other mammals, two sections of frontal skull bone aren't fused together until after birth, so there's a seam; and unique placement of teeth in the jaw.
The fossil evidence from Asia is too fragmentary to see these features, Delson said. ''They just don't have the morphological characteristics," he said.
But Marivaux said that because the Asian fossils are much older -- from the middle of the Eocene Era, 55 million to 34 million years ago -- it makes sense that they would have different features. He argues that the much more recent Fayum animals just hadn't evolved those features yet.
The anthropoids he found in South Asia ''are very primitive," he said. ''Why should they display the characteristics of the advanced forms found much more recently [in Egypt]?"
Marivaux's case that the Asian fossils are anthropoids is based on subtle interpretation of the fragments of ankle bones, skull bits, and teeth he and others have found.
''Some people deny the new paleontological evidence. Why? Probably because they are jealous," he said, that he found the fossils and they didn't.
The argument is not purely semantics. Every bit of evidence that connects what came before to what came after helps confirm the progressive steps of evolution, which adds further factual support to the whole theory of evolution. And, as Fleagle said, ''If you're curious about where you came from, and your ancestry, this gives you some insight.
Answering the Asia-versus-Africa question about our most ancient ancestors ''won't throw much light on modern people," Delson added. ''But knowing where the anthropoid branch of primates began may tell us more in terms of filling in the gaps of the general story of human evolution."
[Source]
0 comments:
Post a Comment