The new report, by a paleoanthropologist from Germany’s Max Planck Institute of Evolutionary Biology, claims that there is no discernible connection of the extinction of our closest evolutionary relatives to extreme climate change.
Published recently in the journal Nature, the new research is centered on the comparing of evidence gathered from deep-sea core drillings in Venezuela, and from sediments found at Gorham’s Cave, in southern Gibraltar, thought to be one of the last places inhabited by Neanderthals on the European continent.
Using radiocarbon dates of 32,000, 28,000 and 24,000 (which are thought to mark the demise of our stocky prehistoric cousins), professor Katerina Harvati and her team compared them to past climate data gathered from the deep-sea drilling cores.
"The more controversial date of circa 24,000 years ago, places the last Neanderthals just before a major climate shift that would have been characterized by a large expansion of ice sheets and the onset of cold conditions in northern Europe,” according to Harvati, who co- authored the paper.
"But Gibraltar's climate would have remained relatively unaffected, perhaps as a result of warm water from the sub-tropical Atlantic entering the western Mediterranean,” she said
Converting a radiocarbon date into a calendar year can be tricky, but the team came up with a method to correlate estimated dates of the species’ demise with records of past climate. The first two dates, 32,000 and 28,000 didn’t correlate with any extreme climatic changes. And the earlier date, 24,000, corresponded to a paleoclimate occurring before the onset of colder, more severe weather in northern Europe, and ice-sheet advancement.
But even then the authors say that the onset was hardly a sudden ice-age, but rather the beginning of a 1000-year gradual change in climate.
So if a sudden shift in climate didn’t kill off the Neanderthals, what did? The question remains open.
"This eliminates catastrophic climate change as a cause for extinction, but this leaves a whole range of other possibilities,” Harvati said.
The two species of hominids had previously been thought to have evolved one from the other (H. erectus from H. habilis), but the new evidence appears to show they co-existed in the same lake region for more than half a million years.
A broken upper jawbone from H. habilis and an intact H. erectus skull were uncovered in the Kenya’s Turkana basin area, and date back to about 1.44 million years and 1.55 million years respectively. Geologists used radiometric dating of volcanic ash deposits to determine the age of the remains. The H. habilis fossil is the youngest of that species ever found.
"Their co-existence makes it unlikely that Homo erectus evolved from Homo habilis," said co-author Professor Meave Leakey, paleontologist the Koobi Fora Research Project. She and her paleontologist daughter, Louise, are co-directors of the research organization.
The fossils were found in 2000 but went through extensive preparation and study before the results were published.
The erectus skull contains the distinctive cranium ridge, and jaw and teeth features found in the species, but the skull’s small size baffles the researchers.
“What is truly striking about this fossil is its size,” said professor Fred Spoor who co-authored the paper. “It is the smallest Homo erectus found thus far anywhere in the world.”
Spoor, a professor of developmental biology at University London College, dismissed that the smaller size could be due to it being from an under-developed specimen.
"By studying how the skull bones are fused together we discovered it belonged to a fully grown young adult rather than a developing juvenile erectus," he said.
Sexual dimorphism (the size disparity between the male and female of a species) could be a factor in the skull’s size, but would mean all other erectus remains found until now have all been male. Some scientists not involved in the study think this may be the case.
With the two hominids inhabiting the same region for such a long a time and still remaining separate suggests the two species didn’t compete directly for resources.
Spoor conjectured on the possibility that an isolated population of Homo habilis living in another part of Africa away from the Turkana basin may have evolved into Homo erectus.
"But that is a much more complex proposition," Spoor said. "The easiest way to interpret these fossils is that there was an ancestral species that gave rise to both of them somewhere between two and three million years ago."
The researchers’ results appeared in the science journal Nature.
The fossil including an entire skull, torso, shoulder blade and various limbs was discovered at Dikaka, some 400 kms northeast of the capital Addis Ababa near the Awash river in the Rift Valley.
"The finding is the most complete hominid skeleton ever found in the world," Zeresenay Alemseged, head of the Paleoanthropological Research Team, told a news conference. Reuters
The fossil has been named "Selam", which means peace in Ethiopia's official Amharic language.
"The Dikika girl stands as one of the major discoveries in the history of palaeoanthropology," research team leader Zeresenay Alemseged said, citing the remarkably well-preserved condition of the bones, the geological age and completeness of the specimen.Cosmos Magazine
The following is the abstract of the original article describing the baby, which was authored by Zeresenay Alemseged, Fred Spoor, William H. Kimbel, René Bobe, Denis Geraads, Denné Reed and Jonathan G. Wynn, and appeared in Nature on September 20, 2006.
"Understanding changes in ontogenetic development is central to the study of human evolution. With the exception of Neanderthals, the growth patterns of fossil hominins have not been studied comprehensively because the fossil record currently lacks specimens that document both cranial and postcranial development at young ontogenetic stages. Here we describe a well-preserved 3.3-million-year-old juvenile partial skeleton of Australopithecus afarensis discovered in the Dikika research area of Ethiopia. The skull of the approximately three-year-old presumed female shows that most features diagnostic of the species are evident even at this early stage of development. The find includes many previously unknown skeletal elements from the Pliocene hominin record, including a hyoid bone that has a typical African ape morphology. The foot and other evidence from the lower limb provide clear evidence for bipedal locomotion, but the gorilla-like scapula and long and curved manual phalanges raise new questions about the importance of arboreal behaviour in the A. afarensis locomotor repertoire."
Additional reading: BBC News
The University of Witwatersrand in Johannesburg South Africa has long been known for its impressive discoveries related to human evolution. Discoveries from Witwatersrand related to human evolution typically emphasized the importance of not only Africa but South Africa in the development of early man. Many of the more famous discoveries related to Paleoanthropology or the study of human evolution come from East Africa — where researchers have discovered, and continue to discover, some of the best evidence for human origins in Africa. Researchers further south, however, continued to argue that fossil discoveries from South Africa should not be discounted from the developing picture of the history of early man.
One of the most significant South African discoveries was the Taung child, which was discovered in 1924 and was given its name when the first researchers to examine the fossil concluded that the specimen was so small because it was a child. This week, researchers from Witwatersrand are announcing that the Taung child could have been killed by a large bird. Yahoo News is reporting that by studying the hunting abilities of modern eagles in West Africa, researchers determined what signs would be left behind on a skull of an animal that was killed by a predatory bird. Armed with this new knowledge, Physical Anthropologists reexamined the Taung child and found traces of cuts behind the eye sockets. Even though the specimen has surely been examined hundreds of times since its discovery, nobody had really noticed the marks before.
Discoveries like this one prove that new discoveries and interpretations can be made by simply reexamining old discoveries with a fresh pair of eyes. No pun intended.
In the field of paleoanthropology, or the scientific study of extinct members of human ancestry, scientists are often asked to stake their reputations on a single claim or hypothesis. The interesting thing about the claims that scholars attempt to make is that they are often based on the very small number of specimens that are available for research. This atmosphere often creates an intense series of lively debates between scholars over the interpretation of their sometimes limited data.