My great-great-grandfather… the Neanderthal?

As a retired physician, I sometimes answer questions related to medical issues. People often ask about their DNA results after finding a 4% genetic contribution from some unexpected source.

Often, this is related to Neanderthal genes, which show up consistently in people from Europe and Asia — but not at all in people from Africa.

A fascinating new bit of scientific data shows that the European and Asian populations got cozy with Neanderthals in Europe and Asia around 40,000 years ago. Enough to impart a hefty donation of Neanderthal DNA to the European and Asian populations.

This was first reported in 2010 after two events occurred. One, skeletons from Neanderthal burials were being discovered. Two, researchers for the first time could collect DNA from these skeletal remains. The DNA was in good enough shape so that it could be sequenced. After sequencing the 40,000-year-old DNA, scientists compared it to modern DNA and discovered a 4% match.

Neanderthals had carved out a niche for themselves during the Ice Age in the hinterlands of Europe and Asia. They hunted deer and mammoths across the steppes of Eurasia and into Siberia. The homo sapiens were newcomers to their lands, migrating from more southern ranges.

Full-blooded Neanderthals became extinct around 37,000 years ago. The Neanderthals only disappeared when the newcomers from warmer southern climes moved into their territory.  No one knows whether the extinction was due to insufficient population or attacks by the new migrants. Scientists are invoking a shallow gene pool theory more and more, hypothesizing that the numbers of Neanderthals had diminished even before the migrants arrived. There were too few of them to procreate and produce healthy offspring. 

What advantage did Neanderthal genes offer to the homo sapiens genome? Neanderthal genes could have conferred a survival advantage in the cold northern reaches of Europe and Asia. The genes could have given a boost to the immune system, protecting humans from pathogens that would otherwise kill them. Or perhaps the genes offered an enhanced ability to survive in a colder climate.

The Neanderthals, by the way, have been unfairly characterized as crude cavemen. They had bigger brains than we homo sapiens have; they were taller and stronger than we are; some of them had red hair and green eyes or pale skin.  They buried their dead in graves, sometimes with gifts such as stone axes. They left behind paintings of animals on the walls of caves and fashioned clothes to keep them warm.

The bottom line in these genetic studies is that populations are fluid due to migrants or conquerors. All of humanity is a mixture of different ethnicities, or in this example, even species. Up until now, we had considered Neanderthals a separate species from ours. Separate species means you cannot make babies together; at least not babies that can themselves reproduce. So we must be more closely related to Neanderthals than we thought, for the genes to have been shared and retained in our DNA.