I Voted For W.
Posted on 03/18/2008 7:11:34 AM PDT by blam
Skull Changes Show Time of Human-Neandertal Split
Scott Norris
for National Geographic News
March 17, 2008
Gradual changes in human skull size and shape suggest a split between humans and Neandertals (often spelled Neanderthals) about 300,000 to 400,000 years ago, according to a new study.
The work provides the first estimate a divergence date for modern humans and Neandertals based on the rate of change of physical characteristics.
Genetic Drift
Just as DNA changes accumulate over time and provide a kind of "molecular clock" by which the separation of closely related species can be dated, evolved differences in physical form can provide similar information, researchers say.
But that is true only if the differences are due to the random process of "genetic drift," and not driven by natural selection, said study lead author Tim Weaver of the University of California Davis.
During genetic drift, different traits accumulate in separate populations by the spread of chance mutations—not because the traits provide any individual advantage in survival or reproduction.
The new study builds on previous work by Weaver's team suggesting that such random genetic changes are the reason people no longer sport the low forehead and protruding brow of our Neandertal relatives.
If differences in human skulls are due to genetic drift, Weaver said, "then the amount of divergence will be proportional to the amount of time elapsed since the ancestors of Neandertals and modern humans [separated] from each other."
The study by Weaver's team appears this week in the journal Proceedings of the National Academy of Sciences.
The new study is based on a series of 37 measurements of the modern human and Neandertal skulls.
For instance, researchers studied the width of the jaw and eye sockets and the distance between the various bones that make up the cranium.
Different human populations today have, on average, slight differences in cranial features. Our heads are not all shaped exactly the same—and neither are our genes.
Scientists can use changes in DNA sequences to estimate the amount of time that has passed since present-day human populations began to diverge.
With this information, Weaver's team was able to measure the rate at which changes in skull form have occurred.
Knowing that rate allowed the researchers to plot the differences between humans and Neandertals backward in time and determine when the two groups separated from one another.
"The striking finding is that we obtained such similar dates to those from DNA sequences by assuming that [skull form] diverged by genetic drift," Weaver said.
Erik Trinkaus is a Neandertal expert at Washington University in St. Louis.
The new study by Weaver's team "is valid in indicating that those aspects of the human cranium that are likely to be governed by random processes, such as drift, are in agreement with … genetic analyses," he said.
"Both of them are [also] in general agreement with the fossil record, which indicates that you start getting divergent aspects of human anatomy in Africa and Europe 300,000 to 500,000 years ago."
Not so Random
Not all changes in the human skull have been random.
The large heads and brains of both humans and Neandertals result from natural selection that occurred earlier in our evolutionary history, experts say.
Once these features evolved, however, the main role of natural selection on the skull has been to constrain its dimensions to a range of variation necessary to accommodate and protect the brain, Weaver said.
"Within this range, cranial form may have virtually no influence on which individuals survive and reproduce," he noted.
"Under these circumstances, changes in cranial form will be due to chance."
GGG Ping.
Sorry, but I live in Texas. The Neanderthals are still around. You see them at 2am in WalMart.
!! My mother’s a pale redhead. Haha, this’ll be fun.
Ah, the great god of random chance and natural selection.
The oldest real evidence of modern man on the planet even by conventional dating schemes is about 30K years.....
I always thought the major difference between man and animals had to do more with the way the brain was wired than the physical characteristics of the being...
I don’t think you can tell that by the size of the brain or shape of the scull.
I dunno, that's one shapely scull.
Changes is species is not sound science. Small adaptations occur but there is no major redesigning of the species. changes are vertical in nature not horizontal ( one species does not turn into another ).
You must have been into the one in Livingston. We stopped in there a few years back while traveling about 1am and you have never seen such a sight. I thought we were on the set of Deliverance. There were 14 year old girls with obviously older men, folks with no shoes on ( at least more shoes than teeth in some cases ), kids in nothing but diapers running everywhere, and obvious signs of inbreeding. We hurriedly got our stuff and left.
"God does not play dice with the Universe" ~ Albert Einstein
Sorry. Einstein was wrong. God does nothing but dice with the Universe.
Ask Job...
Sorry, wrong.
You keep dropping these one-liners on the science threads but you don't seem to want to back them up. Got any evidence for that statement?
The Neandertal EnigmaFrayer's own reading of the record reveals a number of overlooked traits that clearly and specifically link the Neandertals to the Cro-Magnons. One such trait is the shape of the opening of the nerve canal in the lower jaw, a spot where dentists often give a pain-blocking injection. In many Neandertal, the upper portion of the opening is covered by a broad bony ridge, a curious feature also carried by a significant number of Cro-Magnons. But none of the alleged 'ancestors of us all' fossils from Africa have it, and it is extremely rare in modern people outside Europe." [pp 126-127]
by James Shreeve
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Thanks Renfield and Blam. |
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Would that cause a splitting headache?
[singing] Genes. My baby’s got me locked up in genes.
There’s basically no real basis for any of these dates you see on age estimates for most of the hominid remains in the world. RC dating even in theory is only good to around 50K years and the decay methods you read about for much older things don’t apply to hominid remains. Aside from everything else Gunnar Heinsohn has demonstrated that the stratigraphical basis for some of the age estimates involving neanderthal remains in caves are totally fubar and that there is no defensible basis for assigning more than about 100 years to a layering system which is normally assumed to involve about 60,000 years; that would be in “Wie Alt Ist Das Menschengeschlect?” The counts of tools and paraphernalia corresponds to about 100 years and not 60,000.
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