"We can say pretty absolutely that Neandertals didn't contribute mitochondrial DNA to modern humans, but that's just one locus and doesn't carry very strong implications for the rest of the genome," said Henry Harpending, an anthropologist at the University of Utah. "I'm not saying they did interbreed, it's just that mtDNA is a restricted data set."
Typically, if there is interbreeding between two groups of unequal status, it often occurs between the males of the more developed culture and the females of the less developed culture.
"An article was recently published speculating that the selective advantage that modern humans had was reproductive; that the development of a broader pelvis and wider birth canal to accommodate bigger skulls and larger brains made the difference," said Harpending. "If that were the case, it would be easy to imagine that Neandertal women breeding with anatomically modern men would have had a real hard time, and mtDNA might not show up in the modern human genome."
Multi-regional proponents say the lack of similar mtDNA between Neandertals and Cro-Magnons doesn't answer the question of interbreeding.
"What multi-regionalists have been saying all along is that it's about mixture and evolution; that there was gene flow and that Neandertals are one of the ancestors of modern humans," said Milford Wolpoff, a paleontologist at the University of Michigan. "What these data show is that people who lived 20,000 years ago look [genetically] more like people today than the people who lived 45,000 years ago."
"It seems to me that's proving the obvious. It's not telling us that much about the progress in evolution," he said. "You would expect Neandertals to look more and more like modern humans as time goes on."
Looking to the Future
The analysis of ancient nuclear DNA is not technically feasible at the moment, and probably won't be anytime in the near future, the researchers say. But advances in the field of genetics and the mapping of the human genome has provided a flood of information that may someday yield the answers.
"What we need now is to find our way through the databases," said Harpending. "None of the models we have now can explain all of the evidence."
More Information About Human Origins
Cannibalism Normal for Early Humans?
Neandertals Had Highly Capable Hands, Study Says
Did Neandertals Lack Smarts to Survive?
Java Skull Raises Questions on Human Family Tree
First Humans in Australia Dated to 50,000 Years Ago
1.8 Million-Year-Old Hominid Jaw Found
When Did "Modern" Behavior Emerge in Humans?
Documentary Redraws Human's Family Tree
Fossil Implies Our Early Kin Lived in Trees, Study Says
Controversy Over Famed Ancient Skull: Ape or Human?
Skull Fossil Opens Window Into Early Period of Human Origins
Skull Fossil Challenges Out-of-Africa Theory
New Study Supports Idea That Primates, Dinosaurs Coexisted
Human Fossil Adds Fuel to Evolution Debate
Did Our Species Mate With Other Human Species?
Did Humans and Neandertals Battle for Control of the Middle East?
Killer Cats Hunted Human Ancestors
Adolescence Came Late in Human Evolution, Study Shows
Viewpoint: Is It Time to Revise the System of Scientific Naming?
African Bone Tools Dispute Key Idea About Human Evolution
Africa's Imperiled Rock Art Documented Before it Disappears
Bones, Tools Push Back Human Settlement in Arctic Region
Oldest Asian Tools Show Early Human Tolerance of Variable Climate
Telltale Face Betrays Neandertals as Non-Human
Fossils From Ethiopia May Be Earliest Human Ancestor
New Face Added to Humankind's Family Tree
Discoveries Breathe New Life into Human Origins Debate
Additional National Geographic Resources
Interactive Feature: Outpost: In Search of Human Origins
National Geographic magazine online: Who Were the First Americans?