A question that has aroused many people is why humans do not have much Neanderthal DNA in their genome since Neanderthals and humans interbred thousands of years ago. Neanderthals lived in colder climates such as Eurasia and evolved with barrel chests, large skulls and strong hands. Comparatively, modern humans lived in Africa evolving with shorter faces, more prominent chins and slender limbs. These two species interbred around 50,000 years ago which lead to modern humans evolving and spreading out into Africa. The interbreeding of these two species has caused a lot of confusion in the scientific world. That is because today, only 4% of the genes in non-Africans have a Neanderthal origin. Scientists are trying to find out why only 4% of the DNA exists from Neanderthals and where the rest of it went. More importantly, the main question is why the Neanderthal-human hybrid does not exist today. Two studies have essentially shown one simple answer. The population for Neanderthals was much smaller than the population of humans which supports the fact that natural selection is less effective in smaller populations. The factor that contributed to a smaller population of Neanderthals was the conditions that they were living in at the time. Neanderthals lived in more rigid conditions than the modern humans did. This resulted in the Neanderthals being more inbred which also caused them to have more mutations such as increasing the risk of diseases. In 2014, a genetics professor David Reich and his colleagues found out that the Neanderthal DNA was located much farther in the human genome from the important genes. This discovery supported the fact that Natural selection was working against Neanderthal DNA.
Dr. Juric and Dr. Coop analyzed the frequency of Neanderthal ancestry along the human genome because they were sure that the population size was a very important factor. They found that Neanderthals had a greater prevalence of disadvantageous genes. Similarly, postdoctoral student Kelly Harris stated that the simulations prove that early Neanderthal-human hybrids would have been much less fit than pure humans. So either way, the amount of Neanderthal DNA would have decreased in humans. Dr. Reich concludes by stating what a "strange phenomenon" this is. I think it is fascinating that the rough environment that Neanderthals lived in ultimately effected the amount of DNA that has been passed down to modern humans.