Assimilation or replacement - a study about Neanderthals and modern humans

The Neanderthals lived in Europe and the Near East for at least 250,000 years and they outdared several climate changes. They were capable of surviving in a harsh, cold environment and were well adapted to it – cultural and morphological. Thus, the Neanderthals have been proven to be a successful human kind. But why then did they disappear so quickly and without a trace just between 40,000 and 28,000 yr BP (= years before present) [8]?
One possible answer is that modern humans starting to invade the Near East and Europe out of Africa 45,000 to 40,000 yr BP have outcompeted them, due to higher cultural and mental abilities, using the resources in a more efficient way than the Neanderthals. But is this really true? Have modern humans really had higher abilities? Did they admix with the local Neanderthal populations, integrating the native genes in their gene pool? Or did modern humans not interbreed with them?
And – the big question: were Neanderthals and anatomically modern humans distinct species or just local variants of the same species?
To bring more light into this scenario, these questions will be answered in the following chapters using genetic, morphological and simulation-data that has been brought up by several researchers over the last years.
Answering these fundamental questions also lies in the range of basic needs of human mind: we all want to know where we come from, who was our ancestor and who was it not. To realize which strange ways evolution sometimes takes and to determine what really happened is for sure an exciting thing, and that is exactly what researchers do when they trace human evolution back to the point when Neanderthals and modern humans met in Europe during the last ice age. Only one of them should survive this meeting, and to determine why and how this happened I will start with the description and comparison of the two main characters.