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The Neanderthal-Human Split: (Very) Ancient History

Submitted by coldrum on Tuesday, 25 March 2008  Page Views: 1928

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Neanderthals and humans once shared a common ancestor, but we split from the stocky, hairy hominid group as long as 400,000 to 350,000 years ago, concludes a new study.



That estimate matches prior DNA studies, putting a date to the time when human beings first emerged on the planet. But would these first humans have been anatomically just like us? Probably not, suggests lead author Timothy Weaver, an anthropologist at the University of California at Davis.

"Early fossils along this lineage are quite different from later ones," he told Discovery News.

Fast evolution, in fact, probably drove the initial Neanderthal/human divergence, which likely began as genetic drift -- random changes in DNA. As the two groups parted ways, their changing environments likely drove more substantial changes in body shape and size, in response to differing needs.

Weaver and colleagues Charles Roseman and Chris Stringer created a model to determine how long it would have taken genetic drift to create the cranial differences observed between Neanderthal and modern human skeletons.

The model used prior information on how microsatellites, aka "junk DNA," can change, or drift, over time in a species. Over time, those changes can accumulate enough for an entirely new species to evolve.

The researchers applied the model to 37 cranial measurements collected on 2,524 modern and 20 Neanderthal specimens. Their findings are published in this week's Proceedings of the National Academy of Sciences.

Read more at Discovery News
Contributor Bio for coldrum: Based in Milkyway, contributing since 2002. Favourite site: Avebury.

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"The Neanderthal-Human Split: (Very) Ancient History" | Login/Create an Account | 3 News and Comments
  
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Neanderthals were separate species, new study finds by coldrum on Wednesday, 21 May 2008
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Neanderthals were separate species, new study finds

A new, simplified family tree of humanity has dealt a blow to those who contend that the enigmatic hominids known as Neanderthals intermingled with our forebears.

Neanderthals were a separate species to Homo sapiens, as anatomically modern humans are known, rather than offshoots of the same species, the new organigram published Sunday by the journal Nature declares.

The method, invented by evolutionary analysts in Argentina, marks a break with the conventional technique by which anthropologists chart the twists and turns of the human odyssey.

That technique typically divides the genus Homo into various classifications according to the shape of key facial features -- "flat-faced," "protruding-faced" and so on.

Reconciling these diverse classifications from a tiny number of specimens spanning millions of years has led to lots of claims and counter-claims, as well as much confusion in the general public, about how we came to be here.

Various species of Homo have been put up for the crown of being our direct ancestor, only to find themselves dismissed by critics as failed branches of the Homo tree.

The authors of the new study, led by Rolando Gonzalez-Jose at the Patagonian National Centre at Puerto Madryn, Argentina, say the problem with the conventional method is that, under evolution, facial traits do not appear out of the blue but result from continuous change.

So the arrival of a specimen that has some relatively minor change of feature as compared to others should not be automatically held up as representing a new species, they argue.

The team goes back over the same well-known set of specimens, but uses a different approach to analyse it, focussing in particular on a set of fundamental yet long-term changes in skull shape.

They took digital 3D images of the casts of 17 hominid specimens as well as from a gorilla, chimpanzee and H. sapiens.

The images were then crunched through a computer model to compare four fundamental variables -- the skull's roundness and base, the protrusion of the jaw, and facial retraction, which is the position of the face relative to the cranial base.

When other phylotogenic techniques are used, the outcome is a family tree whose main lines closely mirror existing ones but offers a clearer view as to how the evolutionary path unfolded.

The paper suggests that, after evolving from the hominid Australopithecus afarensis, the first member of Homo, H. habilis, arose between 1.5 and 2.1 million years ago.

We are direct linear descendants of H. habilis. H. sapiens started to show up around 200,000 years ago.

None of the species currently assigned to Homo are discarded, though.

On the other hand, the Neanderthals are declared "chronological variants inside a single biological heritage," in other words, evolutionary cousins but still a separate species from us.

The squat, low-browed Neanderthals lived in parts of Europe, Central Asia and the Middle East for around 170,000 but traces of them disappear some 28,000 years ago, their last known refuge being Gibraltar.

Why they died out is a matter of furious debate, because they co-existed alongside anatomically modern man.

Some opinions aver that the Neanderthals were slowly wiped out by the smarter H. sapiens in the competition for resources.

Other contend that we and the Neanderthals were more than just kissing cousins. Interbreeding took place, which explains why the Neanderthal line died out, but implies that we could have Neanderthal inheritage in our genome today, goes this theory.

http://news.yahoo.com/s/afp/20080505/ts_afp/scienceanthropologyneanderthals
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Skulls Of Modern Humans And Ancient Neanderthals Evolved Differently by coldrum on Tuesday, 20 May 2008
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Skulls Of Modern Humans And Ancient Neanderthals Evolved Differently

Skulls Of Modern Humans And Ancient Neanderthals Evolved Differently Because Of Chance, Not Natural Selection

New research led by UC Davis anthropologist Tim Weaver adds to the evidence that chance, rather than natural selection, best explains why the skulls of modern humans and ancient Neanderthals evolved differently. The findings may alter how anthropologists think about human evolution.

Weaver's study appears in the March 17 issue of the Proceedings of the National Academy of Sciences. It builds on findings from a study he and his colleagues published last year in the Journal of Human Evolution, in which the team compared cranial measurements of 2,524 modern human skulls and 20 Neanderthal specimens. The researchers concluded that random genetic change, or genetic drift, most likely account for the cranial differences.

In their new study, Weaver and his colleagues crunched their fossil data using sophisticated mathematical models -- and calculated that Neanderthals and modern humans split about 370,000 years ago. The estimate is very close to estimates derived by other researchers who have dated the split based on clues from ancient Neanderthal and modern-day human DNA sequences.

The close correlation of the two estimates -- one based on studying bones, one based on studying genes -- demonstrates that the fossil record and analyses of DNA sequences give a consistent picture of human evolution during this time period.

"A take-home message may be that we should reconsider the idea that all morphological (physical) changes are due to natural selection, and instead consider that some of them may be due to genetic drift," Weaver said. "This may have interesting implications for our understanding of human evolution."

Weaver conducted the research with Charles Roseman, an anthropologist at the University of Illinois at Urbana-Champaign, and Chris Stringer, a paleontologist at the Natural History Museum in London.

http://www.sciencedaily.com/releases/2008/03/080319104600.htm
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Out of Africa, Not Once But Twice by Andy B on Tuesday, 25 March 2008
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Modern humans are known to have left Africa in a wave of migration around 50,000 years ago, but another, smaller group -- possibly a different subspecies -- left the continent 50,000 years earlier, suggests a new study.

While all humans today are related to the second "out of Africa" group, it's likely that some populations native to Israel, Jordan, Lebanon, Syria, Australia, New Zealand and Indonesia retain genetic vestiges of the earlier migrants, according to the paper's author, Michael Schillaci.

Schillaci, an assistant professor in the Department of Social Sciences at the University of Toronto, also found the earlier group of emigrants had some genetic similarity to Neanderthals, a hominid that left Africa much earlier, settling in Europe and parts of western and central Asia.

"This could be the byproduct of limited [interbreeding] with Neanderthals, or a shared more recent common ancestry with Neanderthals," he told Discovery News. "Humans and Neanderthals share a common Homo ancestor in Africa at around 500,000 years ago. However, Neanderthals evolved in Europe, while modern humans evolved in Africa."

For the study, he calculated genetic similarity by comparing measurements of the cranium, the part of the skull that encloses the brain. In addition to actual DNA testing, researchers often use such skull measurements to establish relationships between ancient human groups.

Schillaci examined fossils representing at least 28 modern and prehistoric human populations.

The earliest known individuals from the Near East, he found, were genetically similar to the earliest individuals from Australia, New Zealand and Indonesia. All modern-day humans are more similar to Europeans who lived between 40,000 and 10,000 years ago -- after the second wave from Africa.

"The most likely explanation...is that the expansion out of Africa that was ancestral to the early Australasians occurred before the well-accepted expansion at around 50,000 years ago that led to the colonization of Europe," he said, adding that the first populations out of Africa were later "swamped genetically by the subsequent larger expansion."

Based on the findings, which have been accepted for publication in the Journal of Human Evolution, he concludes the first human group to have left Africa "may well have been a separate subspecies" of modern human.

Prior research could support that contention. At an Ethiopian village called Herto, archaeologists recently found fossils of individuals who were more robust than modern humans. They date to 154,000 to 160,000 years ago.

Erik Trinkaus, a professor of physical anthropology at Washington University in St. Louis, thinks the new paper "is an interesting analysis," but he told Discovery News that he hopes it will be redone with more fossils, "a better set of measurements and with the caveat that there is a huge (time) gap between his relevant samples."

Schillaci neglected one of the earliest known Southeast Asian humans in his study, noted Trinkaus.

This individual "predates the Australian fossils and is the only relevant fossil that we have between Israel and Indonesia for the relevant time period," he explained, adding that "we have no relevant fossils between 100,000 and 30,000 from the Levant [Near East] and Australia to sort out what might have been happening there."

Chris Stringer, a paleontologist at the Natural History Museum in London, however, expressed fewer reservations.

"This is a very interesting and important study that provides much food for thought," Stringer told Discovery News. "It revisits in more detail and with new approaches something which several researchers have previously noted -- certain early modern samples...seem closer to very early H. sapiens in Israel and Africa than to other early modern samples around the world."

Stinger isn't yet convinced that the Ethiopian fossils and early Australian/Indonesian individuals provide evidence of a new human subspecies. The rigors of dealing with prehistoric life might have simply resulted in sturdier bodies.

Source:
http://dsc.discovery.com/news/2008/03/14/neanderthal-africa.html
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