Human origin or origins?

homo-sapiensA scientific theory talks about an archaic form of humans that left Africa between one and two million years ago. Also scientists claim that modern humans evolved from them independently and simultaneously in areas from Africa, Europe, and Asia.
Another group of researchers sustain the hypothesis that all modern humans evolved in Africa and then left in several waves of migration replacing all previous species of humans. “Genetic evidence tells us that Homo sapiens are of recent origin and arose in Africa,” said S. Blair Hedges, a molecular biologist at Pennsylvania State University. “African populations have the most ancient alleles (gene pairs that code for specific traits) and the greatest genetic diversity, which means they’re the oldest,” according to Hedges. “Our species probably had arisen by 150,000 years ago, with a population of perhaps 10,000 individuals.”
But Chris Stringer, director of the Human Origins Program at the Natural History Museum in London, said: “The multi-regional model of Homo sapiens evolving globally over a long time scale is certainly dead.” “Given the uncertainties, it isn’t yet possible to establish whether we are entirely recent African in origin—certainly my preference—or whether there was a little bit of hybridization/assimilation” between modern and archaic species,” said Stringer. There is no genetic evidence that supports the idea of intermixing, and several DNA studies argue against it.
Today, there is general agreement that Homo erectus, the ancestor of modern humans, evolved in Africa and gradually expanded to Eurasia beginning about 1.7 million years ago. By around 100,000 years ago, several species of hominids populated the Earth, including Homo sapiens in Africa, Homo erectus in Southeast Asia and China, and Neandertals in Europe. By around 30,000 years ago, the only surviving hominid species was H. sapiens.
Some scientists said that evidence based on DNA in the Y-chromosome indicates that the exodus began between 60,000 and 50,000 years ago and also that the travelers followed the southern coastline of Asia, crossed about 250 kilometers (155 miles) of sea, and colonized Australia by around 50,000 years ago. The Aborigines of Australia, are the descendants of the first wave of migration out of Africa. Many archaeologists disagree, saying the fossil record shows that a first wave of migration occurred around 100,000 years ago.
“Archaeological evidence suggests that there were modern humans in at least two places in the Levant region of the Middle East 90,000 years ago,” said Alison Brooks, a paleoanthropologist at George Washington University in Washington, D.C. “They disappear from the Levant about 10,000 years later, but could have survived further south in Asia—we just have no evidence.” “There’s also evidence,” she added, “of Homo sapiens in Australia 60,000 years ago, and they’d have to go through India and Southeast Asia to get there.”

Wells agrees that there may have been early human forays into the Middle East, but argues that the Levant of 100,000 to 150,000 years ago was essentially an extension of northeastern Africa and was probably part of the original range of early Homo sapiens. These early settlers were replaced by Neandertals in the region about 80,000 years ago.
Richard Klein, an anthropologist at Stanford University, has one explanation for the gap and the subsequent waves of colonization beginning around 45,000 years ago.
He thinks Homo sapiens may have been anatomically modern 150,000 years ago, but did not become behaviorally modern until about 50,000 years ago, when a genetic mutation related to cognition made us smarter. That change in thinking ability enabled modern humans to craft sophisticated tools, build permanent lodgings, hunt more effectively, and possibly develop language and also led to greater travel.

A very well preserved skull of a tiny-brained human ancestor has been recovered from beneath the ruins of a medieval castle in the republic of Georgia. The skull is about 1.8 million years old and it is believed to belong to the first group of humans to migrate out of Africa. This finding raise the hypothesis that the evolution of big brains generated the exodus of early humans out of Africa.
The fossil evidence from Dmanisi includes three skulls, jaw fragments, and many stone tools.
“Before this find, the main reason was that at least these humans had big brains,” said David Lordkipanidze, a paleoanthropologist at the Georgian State Museum in Tbilisi who led the excavation team. “Now this shows that (their brains) were quite small.” The brain of the new specimen from Dmanisi is about half the size of a modern human’s brain. The two skulls found in 1999 at the site are also about 1.8 million years old and had room for substantially larger brains. Dmanisi sits on a promontory formed by the confluence of two rivers between the Black Sea and the Caspian Sea about 50 miles (80 kilometers) southwest of Tbilisi. Archaeologists first began excavating the remains of a 1,000-year-old castle located on the site in 1936. Researchers classified the three skulls as belonging to Homo erectus, but the small brain and other features of the new skull suggest a close resemblance to Homo habilis, which was more apelike with a thin brow, huge canine teeth, and long, dangling arms. The variation among the hominids recovered at Dmanisi makes it difficult to say exactly who these people were, said Lordkipanidze. He stated that the variation may force scientists to rethink the definition of “Homo.” According to the researchers the Dmanisi hominids are among the most primitive individuals attributed to H. erectus and that “it now seems that the first humans to disperse from the African homeland were similar in grade to H. habilis.”
The stone tools found with the hominid remains at Dmanisi similar to the Oldowan set found in the Olduvai Gorge, Tanzania. This means that early humans with primitive technology were able to expand out of Africa, said Lordkipanidze.


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