These extra copies might indicate that people from some parts of the world are resistant to certain diseases because they have a symbiosis with the local disease-causing bacteria or virus, such that their DNA contains multiple copies of the RNA of those viruses/bacteria. There was a sci-fi novel called "Darwins Radio" and sequel "Darwins Children" by Greg Bear where a retrovirus dormant in human DNA was activating sporatically around the world, and causing "Herod's Flu" and huge evolutionary changes in babies born to women with the disease. Of course the book was a major fantasy grown from the core idea.

I'm not saying the new research is backing this idea, but it's certainly suggestive. Mitochondria, which every cell in our bodies has, are actually symbiotic bacteria, just like chloroplasts in plants which convert the sun's energy into plant matter are also symbiotic bacteria fully assimilated into the plant. When a cell divides, it also replicates new symbiotic mitochondria to service the daughter cells. I guess the question is: To what extent are viruses/germs responsible for genetic variations between people from different parts of the world, versus conventional natural selection which is based on climate/food supply/geography or other environmental conditions?