Posted on 03/06/2002 7:38:41 PM PST by ValerieUSA
A new piece of evidence—one sure to prove controversial—has been flung into the human origins debate.
A study published March 7 in Nature presents genetic evidence that humans left Africa in at least three waves of migration. It suggests that modern humans (Homo sapiens) interbred with archaic humans (Homo erectus and Neandertals) who had migrated earlier from Africa, rather than displacing them.
Ancient Origins
In the human origins debate, which has been highly charged for at least 15 years, there is a consensus among scientists that Homo erectus, the precursor to modern humans, originated in Africa and expanded to Eurasia beginning around 1.7 million years ago.
Beyond that, opinions diverge.
There are two main points in contention. The first is whether modern humans evolved solely in Africa and then spread outward, or evolved concurrently in several places around the world.
The second area of controversy is whether modern humans completely replaced archaic forms of humans, or whether the process was one of assimilation, with interbreeding between the two groups.
"There are regions of the world, like the Middle East and Portugal, where some fossils look as if they could have been some kind of mix between archaic and modern people," said Rebecca Cann, a geneticist at the University of Hawaii.
"The question is," she said, "if there was mixing, did some archaic genetic lineages enter the modern human gene pool? If there was mixing and yet we have no evidence of those genes—as is indicated from the mitochondrial DNA and y chromosome data—why not?"
Alan Templeton, a geneticist at Washington University in St. Louis who headed the study reported in Nature, has concluded that yes, there was interbreeding between the different groups. "We are all genetically intertwined into a single long-term evolutionary lineage," he said.
To reach his conclusion, Templeton performed a statistical analysis of 11 different haplotype trees. A haplotype is a block of DNA containing gene variations that researchers believe are passed as a unit to successive generations. By comparing genetic differences in haplotypes of populations, researchers hope to track human evolution.
Templeton also concluded that modern humans left Africa in several waves—the first about 1.7 million years ago, another between 800,000 and 400,000 years ago, and a third between 150,000 and 80,000 years ago.
Alison S. Brooks, a paleoanthropologist at George Washington University, is more cautious about Templeton's conclusions. "Archaeological evidence supports multiple dispersals out of Africa," she said. "The question has always been whether these waves are dead ends. Did all of these people die? Templeton says not really, that every wave bred at least a little bit with those in Eurasia.
"This has not been the majority viewpoint of geneticists up to this point," said Brooks.
Dueling Theories
The fossil record shows that about 100,000 years ago, several species of hominids populated Earth.
Homo sapiens could be found in Africa and the Middle East; Homo erectus, as typified by Java Man and Peking Man, occupied Southeast Asia and China; and Neandertals roamed across Europe.
By about 25,000 years ago, the only hominid species that remained was Homo sapiens. Scientists have conducted a considerable amount of both genetic and archaeological research in an effort to understand how this outcome occurred.
....More at link......
This is the only thing that explains some NFL Linemen and NHL defensemen.;)
Yes, and they call themselves liberals!
Red
Sorry, but that's just total BS. Several recent studies of neanderthal DNA have all indicated that neanderthal DNA is "about halfway between ours and that of a chimpanzee", i.e. we could no more interbreed with neanderthals than swe could with horses. Homo Erectus, of course, if clearly much further removed from us than the neanderthal, and we obvously could not interbreed with him either. The DNA findings explain the anomalous total lack of interbreeding in areas in which humans and neanderthals lived in close proximity for long periods of time. Under such circumstances, interbreeding should have been common, and remains of mixed types should be very easy to find.Sorry, but that's just total BS. There is no Neandertal DNA. There's no way to determine much of anything from mtDNA, other than ruling out or ruling in recent relationships (like Jesse James' remains). Homo Erectus may have been around as recently as 20,000 years ago (not extinct for 100s of 1000s), and there isn't even mtDNA around for Erectus AFAIK. Also, as Erectus is the consensus candidate for the most recent common ancestor (agreed by Multiregionalists and Replacement advoc), OF COURSE the chromosome structure is compatible. My first post in this thread (just a little way up the page) happens to address the rest of the unfounded objections.
George W. Bush will be reelected by a margin of at least ten per cent
If you dropped the Chinese off in the Midwest, they would claim the same thing.
Some Asian races are relatively short, true, but not the Chinese. In general Chinese people are nearly as tall as Americans, and quite tall compared to, say, the Japanese.
Cross-breeding of what??
If you cross a horse and a donkey you get a sterile mule. But some lion-tiger crosses are fertile. So are crosses between different "species" of snakes and fish.
What is a "species"? Are Neaderthals and Homo erectus and modern man really different species?
100,000 years seems like a long time, but from an evolutionary perspective, its not.
I agree that "modern man" whatever that is, originated in Africa. But I don't think you can pinpoint migrations from Africa to the rest of the world in one or two or three exclusive events. Successful dispersal of species does not occur that way. In all probability the three waves concept is a conservative one. My guess is there were numerous waves of migrants and that they were close enough to the Neanderthals to have interbred with them. I'm not so sure about the Homo erectus, but anything is possible.
Looking at reconstructions of Neaderthals and "modern man" as well as their skeletal remains, especially those of later Neanderthals makes them appear very similar.
Put a Neanderthal in a business suit, give him a shave, haircut, nail trim and bath, and he probably would like a very strong modern man.
You want to link to me on the page? How very homo erectus of you! *blush*
I agree.
This explains Ted Danson.
ahhh... just where does the orange face first appear on the human evolution timeline?
Definitely taller than the Japanese, I would agree (they make me feel like a giant when I'm walking there), but not all that tall. I'm average height for an American, but when I'm on a crowded Beijing street my head is floating above the crowd along with the Russians I see there.
Just put him in a tank shirt and sweat shorts and he could be a personal trainer at the gym.
George W. Bush will be reelected by a margin of at least ten per cent
Election 2004 threads on FR
Here's the proof!
Okay, I'm frightened now.
Glad you caught that!
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