A fossilized jawbone of what scientists claim is one of the very first humans has been discovered un Ethiopia.
The 2.8 million-year-old specimen is 400,000 years older than researchers thought that our kind first emerged.
The discovery suggests climate change spurred the transition from tree dweller to upright walker.
Prof. Brian Villmoare of the University of Nevada in Las Vegas said the discovery makes a clear link between an iconic 3.2 million-year-old hominin (human-like primate) discovered in the same area in 1974, called “Lucy”.
The fossil record between the time period when Lucy and her kin were alive and the emergence of Homo erectus (with its relatively large brain and humanlike body proportions) two million years ago is sparse.
The 2.8 million-year-old lower jawbone was found in the Ledi-Geraru research area, Afar Regional State, by Ethiopian student Chalachew Seyoum.
The fossil is of the left side of the lower jaw, along with five teeth. The back molar teeth are smaller than those of other hominins living in the area and are one of the features that distinguish humans from more primitive ancestors, according to Prof. William Kimbel, director of Arizona State University’s Institute of Human Origins.
A computer reconstruction of a skull belonging to the species Homo habilis, which has been published in Nature journal, indicates that it may well have been the evolutionary descendant of the species announced today.
The dating of the jawbone might help answer one of the key questions in human evolution. What caused some apes to climb down from the trees and make their homes on the ground.
A separate study in Science hints that a change in climate might have been a factor. An analysis of the fossilized plant and animal life in the area suggests that what had once been lush forest had become dry grassland.
As the trees made way for vast plains, apes found a way of exploiting the new environmental niche, developing bigger brains and becoming less reliant on having big jaws and teeth by using tools.
According to scientists, there were several different species of humans co-existing in Africa around two million years ago with only one of them surviving and eventually evolving into our species, Homo sapiens. It is as if nature was experimenting with different versions of the same evolutionary configuration until one succeeded.
A new study of Neanderthal skulls suggests that they became extinct because they had larger eyes than our species.
As a result, more of their brain was devoted to seeing in the long, dark nights in Europe, at the expense of high-level processing.
This ability enabled our species, Homo Sapiens, to fashion warmer clothes and develop larger social networks, helping us to survive the ice age in Europe.
The study is published in Proceedings of the Royal Society B Journal.
Neanderthals are a closely related species of human that lived in Europe from around 250,000 years ago. They coexisted and interacted briefly with our species until they went extinct about 28,000 years ago, in part due to an ice age.
The research team explored the idea that the ancestor of Neanderthals left Africa and had to adapt to the longer, darker nights and murkier days of Europe. The result was that Neanderthals evolved larger eyes and a much larger visual processing area at the back of their brains.
The humans that stayed in Africa, on the other hand, continued to enjoy bright and beautiful days and so had no need for such an adaption. Instead, these people, our ancestors, evolved their frontal lobes, associated with higher level thinking, before they spread across the globe.
Eiluned Pearce of Oxford University decided to check this theory. She compared the skulls of 32 Homo sapiens and 13 Neanderthal skulls.
She found that Neanderthals had significantly larger eye sockets – on average 6 mm longer from top to bottom.
Although this seems like a small amount, she said that it was enough for Neanderthals to use significantly more of their brain to process visual information.
“Since Neanderthals evolved at higher latitudes, more of the Neanderthal brain would have been dedicated to vision and body control, leaving less brain to deal with other functions like social networking,” said Eiluned Pearce.
A new study of Neanderthal skulls suggests that they became extinct because they had larger eyes than our species
This is a view backed by Prof. Chris Stringer, who was also involved in the research and is an expert in human origins at the Natural History Museum in London.
“We infer that Neanderthals had a smaller cognitive part of the brain and this would have limited them, including their ability to form larger groups. If you live in a larger group, you need a larger brain in order to process all those extra relationships,” he explained.
The Neanderthals more visually focused brain structure might also have affected their ability to innovate and to adapt to the ice age that was thought to have contributed to their demise.
There is archaeological evidence, for example, that the Homo sapiens that coexisted with Neanderthals had needles which they used to make tailored clothing. This would have kept them much warmer than the wraps thought to have been worn by Neanderthals.
Prof. Chris Stringer said that all these factors together might have given our species a crucial advantage that enabled us to survive.
“Even if you had a small percent better ability to react quickly, to rely on your neighbors to help you survive and to pass on information – all these things together gave the edge to Homo sapiens over Neanderthals, and that may have made a difference to survival.”
The finding runs counter to emerging research that Neanderthals were not the stupid brutish creatures portrayed in Hollywood films, but may well have been as intelligent as our species.
Oxford University’s Prof. Robin Dunbar, who supervised the study, said that the team wanted to avoid restoring the stereotypical image of Neanderthals.
“They were very, very smart, but not quite in the same league as Homo sapiens.”
“That difference might have been enough to tip the balance when things were beginning to get tough at the end of the last ice age,” he said.
Up until now, researchers’ knowledge of Neanderthals’ brains has been based on casts of skulls. This has given an indication of brain size and structure, but has not given any real indication of how the Neanderthal brain functioned differently from ours. The latest study is an imaginative approach in trying to address this issue.
Previous research by Eiluned Pearce has shown that modern humans living at higher latitudes evolved bigger vision areas in the brain to cope with lower light levels. There is no suggestion though that their higher cognitive abilities suffered as a consequence.
Studies on primates have shown that eye size is proportional to the amount of brain space devoted to visual processing. So the researchers made the assumption that this would be true of Neanderthals.