Thursday, October 17, 2013
Skull discovery of 1.8m year old suggests early man was single species
By Kerry Sheridan
Washington (AFP) - A stunningly well-preserved skull from 1.8 million years ago offers new evidence that early man was a single species with a vast array of different looks, researchers said.
With a tiny brain about a third the size of a modern human's, protruding brows and jutting jaws like an ape, the skull was found in the remains of a medieval hilltop city in Dmanisi, Georgia, said the study in the journal Science.
It is one of five early human skulls -- four of which have jaws -- found so far at the site, about 100 kilometers (62 miles) from the capital Tbilisi, along with stone tools that hint at butchery and the bones of big, saber-toothed cats.
Lead researcher David Lordkipanidze, director of the Georgian National Museum, described the group as "the richest and most complete collection of indisputable early Homo remains from any one site."
The skulls vary so much in appearance that under other circumstances, they might have been considered different species, said co-author Christoph Zollikofer of the University of Zurich.
"Yet we know that these individuals came from the same location and the same geological time, so they could, in principle, represent a single population of a single species," he said.
The researchers compared the variation in characteristics of the skulls and found that while their jaw, brow and skull shapes were distinct, their traits were all within the range of what could be expected among members of the same species.
"The five Dmanisi individuals are conspicuously different from each other, but not more different than any five modern human individuals, or five chimpanzee individuals, from a given population," said Zollikofer.
"We conclude that diversity within a species is the rule rather than the exception."
Under that hypothesis, the different lineages some experts have described in Africa -- such as Homo habilis and Homo rudolfensis -- were all just ancient people of the species Homo erectus who looked different from each other.
It also suggests that early members of the modern man's genus Homo, first found in Africa, soon expanded into Asia despite their small brain size.
"We are thrilled about the conclusion they came to. It backs up what we found as well," said Milford Wolpoff, a paleoanthropologist at the University of Michigan.
Wolpoff and Adam Van Arsdale of Wellesley College published a study in the journal Evolution last year that also measured statistical variation in characteristics of early skull fossils in Georgia and East Africa, suggesting a single species and an active process of inter-breeding.
"Everyone knows today you could find your mate from a different continent and it is normal for people to marry outside their local group, outside their religion, outside their culture," Wolpoff told AFP.
"What this really helps show is that this has been the human pattern for most of our history, at least outside of Africa," he added.
"We don't have races. We don't have different subspecies. But it is normal for humans to vary, and they have varied in the past."
But not all experts agree.
"I think that the conclusions that they draw are misguided," said Bernard Wood, director of the hominid paleobiology doctoral program at George Washington University.
"What they have is a creature that we have not seen evidence of before," he said, noting its small head but human-sized body.
"It could be something new and I don't understand why they are reluctant to think it might be."
In fact, the researchers did give it a new name, Homo erectus ergaster georgicus, in a nod to the skull as an early but novel form of Homo erectus found in Georgia.
The name also retracts the unique species status of Homo georgicus given to the jaw that was found in 2000 along with other small, primitive skulls.
The jaw lay a few yards (meters) from where Skull 5, belonging to the same owner, was later discovered in 2005.
Co-author Marcia Ponce de Leon of the University of Zurich said Skull 5 was "perfectly preserved" and "the most complete skull of an adult fossil Homo individual found to date."
Its discovery, in such close quarters with four other individuals, offered researchers a unique opportunity to measure variations in a single population of early Homo, and "to draw new inferences on the evolutionary biology" of our ancestors, she said.
DMANISI, Georgia (AP) — The discovery of a 1.8-million-year-old skull of a human ancestor buried under a medieval Georgian village provides a vivid picture of early evolution and indicates our family tree may have fewer branches than some believe, scientists say.
The fossil is the most complete pre-human skull uncovered. With other partial remains previously found at the rural site, it gives researchers the earliest evidence of human ancestors moving out of Africa and spreading north to the rest of the world, according to a study published Thursday in the journal Science.
The skull and other remains offer a glimpse of a population of pre-humans of various sizes living at the same time — something that scientists had not seen before for such an ancient era. This diversity bolsters one of two competing theories about the way our early ancestors evolved, spreading out more like a tree than a bush.
Nearly all of the previous pre-human discoveries have been fragmented bones, scattered over time and locations — like a smattering of random tweets of our evolutionary history. The findings at Dmanisi are more complete, weaving more of a short story. Before the site was found, the movement from Africa was put at about 1 million years ago.
When examined with the earlier Georgian finds, the skull "shows that this special immigration out of Africa happened much earlier than we thought and a much more primitive group did it," said study lead author David Lordkipanidze, director of the Georgia National Museum. "This is important to understanding human evolution."
For years, some scientists have said humans evolved from only one or two species, much like a tree branches out from a trunk, while others say the process was more like a bush with several offshoots that went nowhere.
Even bush-favoring scientists say these findings show one single species nearly 2 million years ago at the former Soviet republic site. But they disagree that the same conclusion can be said for bones found elsewhere, such as Africa. However, Lordkipanidze and colleagues point out that the skulls found in Georgia are different sizes but are considered to be the same species. So, they reason, it's likely the various skulls found in different places and times in Africa may not be different species, but variations in one species.
To see how a species can vary, just look in the mirror, they said.
"Danny DeVito, Michael Jordan and Shaquille O'Neal are the same species," Lordkipanidze said.
The adult male skull found wasn't from our species, Homo sapiens. It was from an ancestral species — in the same genus or class called Homo — that led to modern humans. Scientists say the Dmanisi population is likely an early part of our long-lived primary ancestral species, Homo erectus.
Tim White of the University of California, Berkeley, wasn't part of the study but praised it as "the first good evidence of what these expanding hominids looked like and what they were doing."
Fred Spoor at the Max Planck Institute in Germany, a competitor and proponent of a busy family tree with many species disagreed with the study's overall conclusion, but he lauded the Georgia skull discovery as critical and even beautiful.
"It really shows the process of evolution in action," he said.
Spoor said it seems to have captured a crucial point in the evolutionary process where our ancestors transitioned from Homo habilis to Homo erectus — although the study authors said that depiction is going a bit too far.
The researchers found the first part of the skull, a large jaw, below a medieval fortress in 2000. Five years later — on Lordkipanidze's 42nd birthday — they unearthed the well-preserved skull, gingerly extracted it, putting it into a cloth-lined case and popped champagne. It matched the jaw perfectly. They were probably separated when our ancestor lost a fight with a hungry carnivore, which pulled apart his skull and jaw bones, Lordkipanidze said.
The skull was from an adult male just shy of 5 feet (1.5 meters) with a massive jaw and big teeth, but a small brain, implying limited thinking capability, said study co-author Marcia Ponce de Leon of the University of Zurich. It also seems to be the point where legs are getting longer, for walking upright, and smaller hips, she said.
"This is a strange combination of features that we didn't know before in early Homo," Ponce de Leon said.
Borenstein reported from Washington.
Journal Science: http://www.sciencemag.org
Seth Borenstein can be followed at http://twitter.com/borenbears