This explains in brief why the Neanderthals died out and when. A large possibility is that high birth rates gave humans an advantage over them. The adults had a relatively equal mortality rate, but infants did not, and so the human population grew while Neanderthals died out.
did they disappear solely because of other hominid species (humans)?
The results showed that Neanderthal DNA is 99.7 percent identical to modern human DNA, versus, for example, 98.8 percent for modern humans and chimps, according to the study.
Neanderthals, like modern humans, are thought to have arisen on the continent.
Though no fossil evidence has been found for Neanderthals and modern humans coexisting in Africa,
interbreeding occurred just after our species had left Africa
Neanderthals, the study team says, probably mixed with early Homo sapiens just after they'd left Africa but before Homo sapiens split into different ethnic groups and scattered around the globe.