Europe and West Asia had long been inhabited by hominids descended from, but rather different to, the early Homo erectus of Africa: they are generally grouped together as archaic Homo sapiens.
From around 200,000 years ago they began to develop a number of distinctive features, such as prominent brow ridges and a generally short, heavy build. They are known colloquially as the Neanderthals (Homo neanderthalensis).
Regarded for a long time as our direct ancestors, opinion now generally views them as a separate, dead-end, species. Conditions were becoming steadily cooler, entering a glacial period. Neanderthals living in Europe, which was strongly affected by the glacial conditions, evolved extreme features advantageous in this environment.
These included a large, flattish nose to warm air as it was breathed in. They were probably able to build up substantial fat reserves which would have helped them to survive periodic food shortages.
In West Asia, less extremely developed Neanderthals apparently coexisted with fully modern humans from around 100,000 years ago.
There is no evidence of interbreeding between these two groups of hominids. Why? If they had become separate species, any attempt at breeding would not have produced fertile offspring.
Even if they were the same species, they may not have recognized each other as 'human': history has many well-documented instances of meetings between peoples who have had difficulty in accepting each other's full humanity - even recently. In later Europe (after 40,000 BC), the situation is more uncertain: did they interbreed?
Many scientists say no but the possibility is still entertained by some. Neanderthals eventually disappeared, probably outcompeted by modern humans.
