But the latest theory wonders if the newcomers brought in new infectious disease did them in, in the same way that infectious disease caused millions of indigenous Amerindians to die after the Spanish arrived.
this was sort of ignored because "experts" insisted that cavemen didn't have infectious disease, and only after en settled down in houses with a pig in the parlor did disease become a problem.
. “Humans migrating out of Africa would have been a significant reservoir of tropical diseases. For the Neanderthal population of Eurasia, adapted to that geographical infectious disease environment, exposure to new pathogens carried out of Africa may have been catastrophic,” Charlotte Houldcroft of the University of Cambridge told The Guardian.
Now there is a question if disease could have been there all along.
Archeology org link
UKGuardian has more details.
The DNA suggestion that sexual relationships might have occured also suggests STD's like herpes simplex might be behind the problem. But they also note TB in there.
the problem: This is only theory. Awaiting proof...
The STD syphillis came into Europe with Colombus' sailors (who when out of work went to Italy, had fun with the lovely ladies of Naples who then entertained the German mercenaries, if I remember the history correctly)
But what about those pre 1492 cases of syphillis found in a few skeletons?
I always assumed it was Yaws, a related disease, but now that DNA suggests some Norwegians and/or Icelanders have Amerindian female ancestry, the theory is that maybe the Vikings brought back not only Amerindian women but syphillis, and that was the source of why a few pre 1492 cases were found.
From Science Frontiers
Recently, however, several additional syphilitic skeletons were dug up at a medieval friary in northeastern Britain. The earliest of these bones date back to about 1300. In fact, the new evidence suggests that there was a geographically limited mini-epidemic of syphilis in Britain about this time. Columbus was now off the hook, but who should be hung on it instead? The Vikings, of course. Viking merchants began visiting this part of England about 1300. And it is now admitted that the Vikings had made it to the New World source of the disease circa 1000. Case closed!? (Malakoff, David; "Columbus, Syphilis, and English Monks," Science. 289:723, 2000.)
The DNA article LINK
I like the part that she came "Voluntarily or non voluntarily": Both Indians and Vikings routinely captured women to use as slaves, a job that included sexual work. Some of course would later marry and be accepted into society, (hence the high amount of Celtic genes in Icelanders)