How did early humans spread?
ONE STUDY, done in Australia, used genetic evidence that suggested “Mungo Man” — a 60,000-year-old skeleton — is genetically unrelated to the Africans believed to have evolved 150,000 or so years ago and later to have settled the world.
Another, published in Friday’s issue of the journal Science, analyzed physical features of early human skulls to suggest there must have been interbreeding among the migrating Africans and resident Neanderthals and even Homo erectus species of pre-humans.
“There never was a marauding band of Africans,” University of Michigan anthropologist Milford Wolpoff, who with colleagues published the latest report in Science, said in a telephone interview.
WAS THERE AN AFRICAN ‘EVE’?
Wolpoff said his findings and the Australian findings indicated humans in Europe and Australia evolved gradually from Homo erectus and Neanderthals, with input from Africans, over time. This view contrasted with theories that Homo erectus and Neanderthals were dead-end species.
“It certainly means that the ‘Eve’ theory, the replacement theory, seems to be wrong,” Wolpoff said.
He argued there was no such thing as a separate species of early humans, despite studies of Neanderthal DNA that showed it to be distinct from the DNA of modern living humans.
“Ancient humans shared genes and behaviors across wide regions of the world, and were not rendered extinct by one ‘lucky group’ that later evolved into us,” Wolpoff said.
The prevailing view, known as the "Out of Africa" theory, holds that modern humans evolved from a common Homo erectus ancestor in Africa. Homo sapiens then left Africa and spread across the world, displacing other hominid species such as Neanderthals.
The competing theory, called "regional continuity," contends that modern humans evolved from Homo erectus in several different places - what are now Africa, Europe and Asia - with interbreeding between the regions.
“The fossils clearly show that more than one ancient group survived and thrived.”
Studies released in November 2000 seemed to reinforce the idea that one man who lived in Africa 59,000 years ago and one woman who lived some 143,000 years ago are the genetic ancestors of all surviving humans.
DID GROUPS INTERMIX?
Peter Underhill of Stanford University in California and colleagues around the world did a genetic analysis of DNA samples from the Y chromosomes of more than 1,000 men, and mitochondrial DNA from women, to reach their conclusion.
Both types of DNA are believed to be passed down from father to son in the case of Y chromosomes, and mother to daughter in the case of mitochondrial DNA, with relatively few changes that can be “clocked” with each generation.
Wolpoff did not dispute these findings, but strongly disagreed with the idea that they meant modern humans from Africa killed or outcompeted earlier human populations, replacing Neanderthals and Homo erectus 50,000 to 60,000 years ago.
“Whenever we come into contact with other people, we share genes,” Wolpoff said. “It is obvious to us that the groups must have intermixed.”
For its study Wolpoff’s group examined fossil skulls from the Mladec cave in the Czech Republic and a skull from the Willandra Lakes region of southeastern Australia.
“We looked at crania,” Wolpoff said. “If you are digging a basement for your house and up came a skeleton and you called in a local forensic scientist, they would go right to the skull. The cranium is the most diagnostic part.”
The researchers compared bumps from the cranium of the Australian fossil to skulls of Homo erectus skeletons from Indonesia. The Czech skulls were Neanderthal and were compared with samples from the Middle East.
“The data imply that both have a dual ancestry,” they wrote in their report.
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