Things sure do change. When I went to school, we still had 9 planets (alas poor Pluto that is another subj however), and things were taught a lot different about early man. The latest version goes something like this: the ancestors of man, walking apes, begain migrating from Africa long ago. Several types of early man evolved from them, including Neandertal which lasted far longer than we have been around something like 400,000 years. Some walking apes however, elected to stay in far southern Africa where they were subjected to a crucible of horrors as the climate changed to desert like conditions and this drought and famine lasted for a long long time. The number of walking apes in this group dwindled to a few hundred, and took up murder and cannibalism among other things to survive.
The became masters of scrounging food and extremely adaptable, also magnificent in development of primitive tools to help in this barely survivable place. And one day the famine and drought ended, and this group EXPLODED in population, spreading like wildfire throughout Africa and later the world. Everything was swept away before them, all other man like creatures disappeared where ever they spread, and they multiplied like fleas, evidently a survival mechanism from the bad days of famine and drought. It wasn't long in Geologic terms before they exploded out of Africa and throughout the word. For these were our ancestors...but what of the others? Well, we know now that all humans except those who stayed in Africa have 2% Neandertal DNA as modern science allowed the DNA mapping of this other early human.
Most likely they just could not compete against the rapidly multiplying "killer apes" from Africa who had far better hunting skills and were much quicker thinking etc. But some interaction did happen ... based on brain mapping from inside the skulls of this alternative early man, the Neandertal were slow thinkers, not big on language, just the opposite of the new quick witted types pouring from Africa ... it is likely they just retreated from the onslaught until they finally faded from History around 25,000 years ago, about the same length of time before that when they first encounters our ancestors. We also now know there was a smaller early man some have called "hobbit" man in Asia. They do not know how long this species survived after H. Sapiens got in the picture. What we do know is that where ever our species spread, all large predators disappear in short order (usually, or at least most of them, unable to compete with a more lethal and efficient killer), then all large prey animals also disappeared, hunted to extinction. Later smaller prey ofen disappeared as well, but the population of man continues to multiply unabated.
yes, only things like the "black death" slowed it down at all. and when we spread into the new world, why it was the Great Extinction soon after, they now think it more from early man than from any weather related condition tho ice ages affected man as well as beast. now we herald the arrival of no 7 billion human on this overcrowded world. What will happen to stop the endless mindless multiplying? Some great plague perhaps? The end of the world as we know it (TEOWAWKI to survival groups) from a new ice age or other disaster? or perhaps the war to end all wars, maybe a new plague to wipe out most of the population? We do not know, but all ages end, including the age of Man. Someday far in the future if the planet survives at all, a different species perhaps of thinking insect who knows, will study our relics and fossils much as we do those of the dinosaurs.
Of course then again some people believe the world is only 4 thousand years old, and for a long time science believed in the Flat Earth with us being the center of the Universe.
my how things do change :)