Still unanswered is the question: What advantage let our ancestors replace the Neanderthals? Did we possess grammatical language where they didn’t, bringing huge survival benefits? Were we more inventive? Did we live in large groups that overwhelmed small families of Neanderthals? Geneticists are already examining ancient human skeletons for genes associated with speech.
You can read the rest @
More likely than not, the advantage was (and is) that we are brutal, heartless killers. We didn't "replace" the Neanderthals, we murdered them.