They were in competition with Sapiens for a similar ecological niche, but Sapiens were more efficient at survival. There was also significant climate change 45 000 years ago, that would have changed the environment and animals/plants available - Neanderthals did not adapt as well as the Sapiens to this. It has also been suggested that small groups of Neanderthals and Sapiens may have fought against each other, with the Sapiens either exterminating or driving the Neanderthals out of the area. These things probably all paid a part, as Neanderthals gradually became more and more isolated in small groups until they finally died out - this took at least 15 000 years. There is some contention that there may have been some interbreeding between Sapiens and Neanderthals at some point - the fossil evidence for this, I believe, was a female child showing both Neanderthal and Sapien traits found in Portugal. Even if this fossil is a Neanderthal-Sapien hybrid, it is highly unlikely that this interbreeding was commonplace; there would be more evidence in the fossil record, if this was the case. In addition, Sapien mitochondrial DNA (mtDNA) has been compared to Neanderthal mtDNA and the dissimilarity suggests a split 500 000 years ago, long before the arrival of Sapiens in Neanderthal-dominated zones some 45 000 years ago. Neanderthals and Sapiens are two distinctive species of the Homo genus, and the evidence suggests that Neanderthal DNA did not merge into the Sapien DNA we have today. Currently, scientists are trying to map the Neanderthal Genome from DNA extracted from bone fragments. It will be interesting to compare this to the Human Genome. More info: http://en.wikipedia.org/wiki/Neanderthal_interaction_with_Cro-Magnons

My view is the scientific version that coincides with the theory of evolution, neanderthal were wiped out by us homosapiens through superior intellect and ingenuity around 45,000 years ago. Homosapiens have since dispersed around the entire globe and have opened a can or two of whoopass on anything that stands in our way. I have yet to see any bible thumpers comment on this one.

You've not met my family!