Neaderthals had brawn, but early humans had a leg up on brains.
Starting at birth, human and Neanderthal brains are similar. During the first year of life, however, the human brain begins more activity in neural circuitry.
Although this doesn't mean that Neanderthals weren't as intelligent as humans, the brains of Homo sapiens developed to support higher-order functions, such as creativity and communication.
Traces of Neanderthal creativity have been found, but no evidence has yet emerged to show they had a complex language of their own.
However, according to one study published in the journal Medical Hypotheses, this lack of cognitive complexity also may have meant that Neanderthals didn't suffer from the same mental disorders as humans.
This distinction, however, proved to be a net gain for humans and may have "helped early Homo sapiens survive in the process of natural selection," according to one report.