Neanderthals and anatomically modern humans (AMH) originated at the end of Riss glaciation by the differencitation of archaic Homo sapiens – genetic differenciation had started some 200 000 - 150 000 years ago. Both groups developed independently – Neanderthals in Europe and Western Asia and AMH in Africa.
AMH and Neanderthals were very close genetically and both groups could potencially interbreed. Paleogenetic studies have proved that both groups had a common ancestor – Homo heidelbergensis/archaic Homo sapiens who had very similar genes, among athers genetical disposition for human speach.
Due to probable sever bottleneck effec on Neanderthal populations after glaciation, they came to the extinction while AMH adapted very well to the environmental changes after glacial maximum connected with supervolcano Toba magaerruption 72 000 year b.p. Neanderthal splited into three groups while had started to colonise World since 65 000 years b.p.