In the extensive family tree of human evolution, the Neanderthal man is one of the closest relatives to the modern Homo sapien sapien. The two species shared a common ancestor 600,000 years ago that contributed similar core characteristics to its distant heirs, including a large brain and bipedalism. However, it wasn’t until modern humans exited Africa and reached Europe, around 45,000 years ago, that the two species existed side-by-side. The Neanderthal species would not survive this coexistence: the species as a distinct entity disappeared within the span of 5,000 years.

The exact date of the interactions between Homo sapien sapien and Homo neanderthalensis has been unclear to scientists. Because the migration of modern humans from Africa is commonly agreed to have occurred some 60,000-50,000 years ago, the fact that the mixing of human and Neanderthal DNA seems to have occurred some 100,000 years ago has puzzled scientists since the discovery of the two species’ interbreeding. How could Neanderthal and Homo sapiens sapiens mix DNA as early as 60,000 years ago, if Homo sapien sapens  didn’t migrate into Europe until 45,000 years? An early and unbeknownst migration of Homo sapien sapien’s is a possibility. However, the presence of Neanderthal DNA in humans as a result of early mating is undeniable.

Two studies have recently uncovered the important medical implications to modern humans of their Neanderthal DNA. After mapping out most of the Neanderthal genome, scientists drew similarities to the DNA from humans of European and Asian descent. From this they concluded that Neanderthals and humans had only mated once modern humans had migrated out of Africa. Anywhere from 1 to 2 percent of the entire genome of a human of non-African descent is made up of Neanderthal DNA. Europeans have about 20 percent less Neanderthal DNA than those of East Asian descent.

Once a more accurate genome was constructed, scientists could draw further conclusions from the comparison of the Homo neanderthalensis and Homo sapien sapien DNA. What they found was a strong correlation between dominant skin and hair genes in living humans of non-African descent and Homo neanderthalensis. Some researchers have considered that the characteristics of modern human’s skin, which plays an important part in protecting against pathogens and cold weather, could have been a useful gene gained from the sturdy Neanderthal, and therefore these genes remained dominant through the process of natural selection. However, the presence of Neanderthal DNA has also been linked to an occurrence of skin lesions.

Other traits gained by Neanderthal DNA have proven to be detrimental to modern human health. For instance, long stretches of some human genomes had significant absences of Neanderthal DNA, suggesting infertility in early modern humans who possessed Neanderthal genes for producing viable sperm and eggs. Ancient Neanderthal DNA could also have had detrimental effects on the mental and physical health of modern humans, contributing to a higher rate of diseases such as depression and hypercoagulation.