Many of us have genes from extinct human species in our DNA. Some of these genes have been helpful, but others seem to be destructive.
When modern humans moved out of Africa between about 60,000 and 100,000 years ago, they met other types of humans who had already made the move to Europe and Asia.
Whatever else went on between Homo Sapiens and these earlier people, some got together and had children, whose genes many of us carry.
Today, the genetic makeup of most people born outside Sub-Saharan Africa is 1 to 4 percent Neanderthal.
And then, to make things even more interesting, along came the Denisovans. What we know of Denisovans is very recent, coming from a finger bone and two teeth found six years ago in Siberia. The Denisovans also left Africa early, and, like their Neanderthal relatives, they interbred with Homo Sapiens.
With time, we are learning that modern humans are indebted to these extinct human species for some of the abilities and some of the problems we find coded into our DNA.
The Altitude Gene
The higher you climb in Earth’s atmosphere, the lower the air pressure gets. This goes on until you reach space, where there’s no air. Every breath we take at high altitudes gives us less air, and less oxygen than at sea level.
Our DNA has an app for that though. At high altitude, our EPAS1 gene fires up, pushing other genes to make extra red blood cells, improving our oxygen take up. The trouble is, these extra cells thicken our blood, making our blood pressure rise unhealthily.
So what happens if you want to live three miles up? Your DNA will need a better app for that!
Tibet is a country whose average elevation is 4900 meters – about 3 miles. It turns out that most people in Tibet have a variant of EPAS1 that allows them to deal with low oxygen with fewer red blood cells than the rest of us. Their blood stays thin and healthy 3 miles up.
And where did this variant come from? It turns out it came from Denisovans; they shared this gene with people who now live in Tibet.
The Immunity Gene
HLA is a gene that helps white blood cells destroy micro-organism intruders in our bodies.
At least one version of HLA is basically absent in Sub-Saharan people. Researchers think that people carrying this gene can thank Neanderthals and Denisovans for it. These hominids had already adapted to infections and diseases found outside Africa. This gene gave any modern humans born with some Neanderthal and Denisovan ancestry a survival advantage.
European people get more than 50 percent of of one HLA genetic variant from interbreeding with Neanderthals and Denisovans. For Asian people it’s as much as 80 percent, and Papua New Guineans 95 percent.
The Hair and Skin Gene
Genes for keratin – the protein in our skin, hair and nails – can have an especially strong Neanderthal influence. Two-thirds of East Asian people have the Neanderthal skin gene POU2F3, while almost three-quarters of European people have the Neanderthal skin-color gene BNC2.
We don’t know exactly what advantages these genes gave people, but the persistence of these genes indicates that they offer quite a powerful boost to survival. It’s possible that Neanderthal adaptations to colder weather encoded in these genes were important.
Even Genetic Ointments Have Flies in Them
The DNA of Homo Sapiens and Neanderthals didn’t mix very well. Long, long stretches of human DNA have no Neanderthal gene input at all. This indicates that genetic modifications in these regions proved negative for survival.
For example, the FOXP2 gene for motor coordination and language and speech has no Neanderthal input.
Furthermore, human male X chromosomes are particularly lacking in Neanderthal input, meaning there’s a good chance that male children of a Human-Neanderthal union had lower fertility than average.
Perhaps only a tiny fraction of the descendents of Human-Neanderthal unions actually prospered.
As if that weren’t enough, auto-immune disorders like type 2 diabetes and Crohn’s disease seem to be more likely if you carry Neanderthal influence.
Other human groupings besides Neanderthals and Denisovans left Africa before Homo Sapiens. Researchers are seeking to obtain their DNA too. Ultimately science would like to determine just how big an effect interbreeding with other species has had on us.