The place of Neanderthals in the story of human evolution has been hotly debated for decades. A distant cousin to our species, Neanderthals had already been in Europe over 250,000 years when Homo sapiens first arrived there 35,000 years ago.
Often called Cro-Magnoids, these first Europeans are believed by many scientists to have out-competed the Neanderthals, gradually driving them to extinction. The alternative theory, that Neanderthals and early humans are more closely related and may have even interbred upon meeting, is less popular, though it hasn’t yet been ruled out. In order to resolve this debate, scientists have turned to genetics and methods of ancient DNA analysis to help them answer the questions surrounding the relationships between Neanderthals and Cro-Magnoids.
However, the practice of extracting and analyzing ancient DNA remains tricky and fraught with skepticism. One of the main problems is contamination – anyone who touches fossilized remains runs the risk of contaminating it with his or her own DNA. So how can we tell if scientists are analyzing the right DNA? A new study in this week’s PLOS One attempts to rectify the contamination problem in a novel way by analyzing the DNA of everyone who touched a fossil for comparison in order to rule out contamination. It will also help us better understand the genetic connection between Cro-Magnoids and Neanderthals.
The Italian team, led by David Caramelli, analyzed DNA from a 28,000-year-old Homo sapiens Cro-Magnoid individual found in Piglacci Cave in Italy. They also analyzed the DNA of everyone who had touched the remains since its 2003 discovery. What they found was that the Cro-Magnoid individual was genetically similar to most modern Europeans. The Cro-Magnoid DNA was also distinct from the researchers’ DNA sequences, showing that none of them had contaminated the sample. When the DNA of the Piglacci Cro-Magnoid individual was compared to previous analyses of Neanderthal DNA, the researchers found that the Cro-Magnoid individual has much more in common genetically with modern European humans than with Neanderthals. These results are important for several reasons.
- First, this is one of the first studies to have obtained a reliable and contaminant-free sample of DNA from a 28,000-year-old Cro-Magnoid. It will hopefully satisfy the skeptics who had claimed contamination will always be a possibility.
- Second, the genetic similarity of the Cro-Magnoid to modern Europeans, combined with its lack of similarity to Neanderthals, helps solidify the theory that the two ancient groups were not closely related. Previous studies comparing Neanderthal DNA to modern human DNA have also turned up no genetic similarity.
- Third, the body of evidence now shows that Neanderthals didn’t contribute any DNA to the Cro-Magnoid OR modern human gene pool. Indeed, Caramelli and his colleagues point out that “the burden of proof is now on those who maintain that Neanderthals might have contributed to the modern gene pool.”
Together, the current scientific evidence suggests that instead of merging with Cro-Magnoids Neanderthals must have simply died out, unable to compete with the Cro-Magnoids’ superior technology and greater population size. The archaeological record shows Neanderthals becoming less and less prevalent around 35,000 years ago, and by 30,000 years ago, they disappear completely.
After their rivals’ disappearance, Cro-Magnoid humans would have to cope with hardships of their own, as the Last Ice Age was approaching its peak. They would be relegated to the southern fringes of Europe for 5,000 years, awaiting the warming temperatures that would allow them to repopulate the continent.