Grine says he first spotted the skull on a bookshelf in a colleague's office in Cape Town, South Africa, and was struck by its similarities to the skulls of the first modern humans found in Europe.
This inspired him to reexamine the skull.
Unable to date it via traditional radiocarbon techniques, Grine sent sand grains pried from the skull's braincase to colleagues at England's Oxford University.
There study co-author Richard Bailey and colleagues used advanced optical and uranium-dating techniques to determine when quartz crystals in the sand were last exposed to sunlight.
The answer36,000 years agogave them the age of the skull.
A study co-author, Katerina Harvati of Germany's Max Planck Institute for Evolutionary Anthropology, then compared the skull to those of Neandertals, members of present-day ethnic groups, and European humans from the Late Ice Age (from about 35,000 to 11,500 years ago).
Grine says the skull bore surprisingly little resemblance to Khoe-San, also known as Bushmen, who have occupied South Africa for at least 15,000 years.
(Read related story about Bushmen: "'Python Cave' Reveals Oldest Human Ritual, Scientists Suggest" [December 22, 2006].)
"Indeed [the skull's] closest affinities were to people from Europe [from the Late Ice Age]," he said.
"This would indicate to me that the skull is very similar to what we would have seen in eastern Africa at the same time."
"In other words, when I look at this skull, it looks like the most recent common ancestor of all modern people."
In a related Science commentary, Goebel, of Texas A&M, wrote, "Here is the first skull of an adult modern human from sub-Saharan Africa that can speak to the relationship of early moderns from Africa and Europe."
Discovery in Russia
In the second Science study, archaeologist Mikhail V. Anikovich and a team of scientists shed light on the possible routes taken by humans after they left Africa.
The team investigated an array of human teeth and artifacts found on the Don River, about 250 miles (400 kilometers) south of Moscow, and dated them to around 45,000 years ago.
Modern humans are believed to have spread into central and western Europe about 40,000 years ago.
Anikovich's finding suggests that humans may have migrated to Eastern Europe slightly before settling the central and western regions of the continent.
"It's surprising to find [modern humans] showing up so early in one of the coldest and driest parts of mid-latitude Europe," said study co-author John Hoffecker, an archaeologist at the University of Colorado at Boulder.
"It is perhaps the last place we would expect some recent immigrants from the tropical zone to be occupying," he added.
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