To this day, modern Europeans and Asians carry about 1-2% Neanderthal DNA. Africans carry only trace amounts. This is likely from Homo sapiens migrating back to their ancestral continent, since Neanderthals never lived in Africa.

Due to a combination of factors, including:

➤ Modern Humans. Neanderthals were outcompeted by Homo sapiens to some extent. But Neanderthals co-existed with modern humans for 3-5,000 years. Considering the two species interbred, Neanderthals may have simply been bred out of existence.

➤ Climate Change. Cooling temperatures may have also been a factor. But Neanderthals had survived multiple glacial periods before encountering modern humans.

➤ Disease. Migrating Homo sapiens introduced new pathogens to Neanderthals. According to some theories, Neanderthals tended to be more geographicaly isolated, leading to less genetic diversity--an important driver for immune system development. But other studies suggest Neanderthals had similar genetic diversity for genes involved with immune response.