Through advances in DNA technology, paleoanthropologists have been able to extract genetic material from some of the Neanderthal bones and compare their genes with those of modern humans. The modern genes, Klein argues, "derive exclusively" from the African ancestors of modern humans, and not from Neanderthals.
That's a highly contentious point. Other anthropologists, such as Erik Trinkaus of the University of Pennsylvania and Milford Wolpoff of the University of Michigan, contend that many modern humans carry at least some genes of Neanderthals mixed in with their own.
Three years ago, Trinkaus and a team of Portuguese scientists described the skeleton of a young boy found in a shallow grave more than 25,000 years old and said they determined from his bones that the youngster was at least part Neanderthal.
In interviews last week, both Trinkaus and Wolpoff argued that this was clear evidence that Neanderthals and modern human ancestors not only lived side by side but also mated and interbred. "The so-called modern humans are a 50-50 combination of ancestry from both peoples," Wolpoff says. "In many Europeans today, you can clearly see the physical features of a Neanderthal past."
To Trinkaus, Klein's conclusions "overemphasize and distort the differences between Neanderthals and modern humans, while downplaying the similarities. The Neanderthals and the Cro-Magnons interbred and produced offspring." From here.
Well, that explains my boss.
Well, the rest of the article is certainly worth reading for context, especially this part:
SIGNIFICANT DIFFERENCES
In fact, Klein contends, DNA extracted from Neanderthal bones shows that the last shared ancestors of the Neanderthals and modern humans lived in Africa at least 500,000 to 600,000 years ago.
There are other major differences, too: Cro-Magnons were the first to produce arrowlike projectiles tipped with ivory and amber, while Neanderthal weapons were only wooden spears sometimes tipped with stone points, Klein says.
The Cro-Magnons also made figurines and created objects of bone, an ability the Neanderthals apparently largely lacked, he says.
As the Cro-Magnon people became more advanced, they learned to build the first true houses, Klein says. By contrast, archaeologists have found only one example where a Neanderthal may have constructed a crude house -- perhaps merely by imitating a Cro-Magnon dwelling, he says.
Except for that one Neanderthal house at a site in central France, "there is little to suggest that Neanderthals could behave in a modern, Upper Paleolithic way," Klein says, referring to the period in which Cro-Magnons thrived. That may well explain why Neanderthals disappeared so quickly and completely, he says.
Then there is the question of language: A recently discovered human gene, called FOXP2, is involved in the human ability to use speech and language. Chimpanzees -- humans' closest animal relatives -- don't carry that gene, but Cro-Magnons may have.
GENES' UNANSWERED QUESTION
Although Wolpoff insists that the bone structure of Neanderthal fossils indicates they too could have been capable of voicing sounds, whether or not they did would become clear only if the FOXP2 gene is ever found in a sample of DNA remaining inside a scrap of Neanderthal bone.
"The main question that remains open," Klein says, "is whether Neanderthal genes explain their failure to compete culturally."
Klein has at least one major ally in F. Clark Howell of UC Berkeley, an eminent paleoanthropologist who has traced human evolution from its beginnings 7 million years ago to the relatively recent rise of the Cro-Magnons and the swift extinction of the Neanderthals.
"I couldn't find a single word in Klein's paper that I could disagree with, " Howell says. "It's a superb piece of work. He's summed it all up with the strongest possible evidence -- both for the known and what's still unknown."
The relevant thread: New analysis shows three human migrations out of Africa, Replacement theory 'demolished'.