In 1987 a team of Berkeley paleontologists led by the late Allan Wilson, did an analysis of mitochondrial DNA from 147 individuals and declared emphatically that the rise of modern humans occurred in Africa within the last 140,00 years and that all present day humans are descended from that population.
In 2000, Eric Lander of MIT's Whitehead Institute Center for Genome Research announced that modern Europeans are descended from no more than a few hundred African who left Africa as recently as 25,000 years ago.
Fast forward to 2007:
A team of scientists who compared the skulls and DNA of human remains from around the world say their results point to modern humans (Homo sapiens) having a single origin in Africa, reported National Geographic July 17 issue. "We are solely children of Africa—with no Neanderthals or island-dwelling "hobbits" in our family tree," according to a new study.
The team led by Andrea Manica at the University of Cambridge,
England, combined analysis of global genetic variations with
comparisons of more than 6,000 skulls from more than a hundred ancient
human populations. The new data support the single origin, or "out of
Africa" theory for anatomically modern humans, which says that these
early humans colonized the planet after spreading out of the continent
some 50,000 years ago.
The new study also looked at 37 measurements from male and female skulls from around the world. The chosen skulls were all less than 2,000 years old, making them better preserved and more likely to give accurate measurements than older skulls.
Wrong says John Hawks, Assistant Professor of Anthropology at the University of Wisconsin—Madison and Erik Trinkaus, Mary Tileston Hemenway Professor of Physical Anthropology, Washington University, considered by many to be the world's most influential scholar of Neanderthal biology and evolution.
Regardless of what morphological or genetic data are offered, the two renowned anthropologists, according to Anthropology.net are skeptical of any research that claims final proof of a single origin for modern humankind, particularly at the date of 50,000 bp, as there are clear indications from Eurasia, Australia and possibly even America, that by this date, modern humans were already living at all these locations, thousands of miles from Africa, and could not possibly have been part of this presumed African exodus.
Another major flaw in the Out of Africa argument is that the skulls chosen are so young in comparison to the populations that were living at 50,000 bp - if they had examined some of the 30,000 - 36,000 year-old skulls from Romania that Erik Trinkaus has been looking at, they would have gained a different impression from the uniform model of skull morphology in moderns than they propose.
Certain genetic and anatomical traits “cannot be explained as a
simple and complete expansion of modern humans out of Africa,” Trinkaus
“The idea that humans get more uniform further from Africa is simply ludicrous,” Trinkaus added, noting that modern-day Chinese and Australian Aborigines look no more similar to each other than do Africans and Europeans.
Manica and colleagues took multiple measurements of more than 4,500 male fossil skulls from 105 populations around the globe. They combined the results with data from studies of global genetic variations in humans, finding that both genetic and skull variability decreased with distance from Africa. So populations in southeastern Africa held the highest variability compared with populations in other countries.
“Humans seem to have poured out of Africa, spread out across the world, but at a really quite uniform rate such that you get this lovely gradual loss of diversity,” said study team member William Amos of the University of Cambridge.
The results held even when the scientists accounted for climate, since climate conditions can lead to changes in skull features. “In very cold climates you tend to generate a slightly thicker brow ridge. Whether or not that’s to keep horrible blizzards out of your eyes, I don’t know,” Amos said.
John Hawks believes the paper is “mistaken.” A major flaw is that the current research is largely based on skull variability. You can’t find the origin of people by measuring the variability of their skulls,”
Differences in skull features are related to genetics, and genetic variation depends on how much mixing occurs with other populations. “The main problem with the paper is that it takes some assumptions from genetics papers of 10 to 15 years ago that we now know are wrong,” Hawks said.
“Africa is ecologically diverse, and cranial variation is a function of environments,” Hawks added. In environments supporting hardy foods such as roots, people would need bigger jaw muscles, and thus larger areas for muscle attachments.
Hawks and Trinkaus imply that the study by Manica is far too simplistic to make any sense.
In his own research, Hawks is finding that natural selection has led
to changes in thousands of genes during only the past few thousand
“I’m really thinking just the opposite of this paper,” Hawks said. “There are differences in the skull between populations, including their variability, but it is mostly due to very recent effects and not the origin of modern humans.”
At the end of the day, a resolution to the Out of Africa debate may
be impossible, he said. Most of the evidence can be interpreted as
supporting both human-origins theories. “It’s really hard to find
observations that distinguish the two,” Hawks said.
“The multiregional idea is identical to the recent African origin idea, except for its prediction that Europeans and Asians were part of the single population of origin and didn’t become extinct.”
Anthropology.net's Tim Jones eloquently sums up the multicultural vs. the out-of-Africa theory: "The idea that much of the Pleistocene was populated by people living in a technical and cultural coma, only wakened from their collective slumber in the Upper Palaeolithic by the sudden pinprick of a modern intelligence which arose from a single location at a specific point in time, (enabling the florescence of our über-selves), is itself long overdue for consignment to the compost heap of old theories based on out-moded concepts."
Posted by Casey Kazan.