Love thy neighbour: Neanderthal inbreeding could be a factor in their demise

19 December 2013

High-quality Neanderthal genetic code reveals interbreeding between small populations of early humans.

Looking at the complete genetic code (the genome) of a Neanderthal woman about 65,000 years old, an international team of researchers discovered that her parents were closely-related, possibly half-siblings. Her genome shows a lack of genetic diversity, meaning there was little mixing of DNA for many generations.

This suggests she lived in a small population, where there was a lot of inbreeding between family members. ‘Despite the fact that her ancestors had ranged widely in Eurasia for tens of millennia, her genomic diversity was less than that found in a small population of hunter-gatherers living in the Amazonian rainforest today,’ said Prof Chris Stringer, Museum human origins expert.

Link to extinction

From tests on humans living today, we know that our ancestors had much larger genetic diversity, suggesting a higher population size.

Small population sizes and inbreeding in Neanderthal populations could be one reason why they died out while ancestral modern humans thrived. ‘Very low levels of diversity are known to be risk factors in extinctions today,’ Prof Stringer said.

Other early humans

The new Neanderthal genome comes from the foot bone of a woman found in a cave in Siberia. Previously, researchers had discovered a completely different early group of humans in the cave, known as Denisovans, from two teeth and the finger bone of a girl who lived around 50,000 years ago.

The new discovery of a Neanderthal woman at the same site, albeit at an earlier time, suggests the two populations may have met and interbred. This is backed up by evidence of shared genetic information between the two groups. There are also other sources of DNA in the Denisovan genome thought to be from a separate interbreeding event with yet another group of ancient humans.

Searching the genome

The new Neanderthal genome is the best quality version yet, and will allow comparison with our own genome. With this information, researchers can see what changes became fixed in us after we split from the other early human groups. This may reveal more reasons why we survived and thrived while the others perished.

Share this

Further information