Neandertals Never Died; Just Their Direct Sirelines and Matrilines

From a piece by Faye Flam in none other than Bloomberg, comes this wonderfully succinct nugget that expresses something that readers of this blog know I ascribe to:

"Scientists have also revised their view of Neanderthal extinction – long attributed to some deficit on their part.  Maybe nothing dramatic happened at all, said Hawks. They would have made up a small fraction of the world’s population, and when larger groups of modern humans joined them in Europe they might have simply been absorbed."

(emphasis added)

This is what I coined the "Demography not Drama" explanation.

It is likely the Neandertal population was tiny, and when modern humans entered Europe, they simply absorbed them, perhaps even absorbed multiple sub-populations (which the genetics data now supports too).

With each generation, there is a great chance that a male line or a female line will disappear.  All it takes is for a man to have only daughters, or a woman to have only sons.  Older lines (which have been around for more generations) face longer odds of appearing to have survived, because each generation increases the chances a line will appear to have died out.  The patrilines and matrilines from a group starting with a smaller population size will also appear to have died out over time.

We have seen this occur in the modern world, both in the example of surnames on isolated islands (the families didn't die out, but the surnames eventually greatly reduced in numbers because of the randomness of males having male children) and with thoroughbreds (the original thoroughbred founding population included 30+ male horses, but only 3 sirelines (akin to surnames or Y-chromosome haplogroups) have survived.

This doesn't mean the others "died out."  Like Neandertals, their genes live on among us.

Another Way of Thinking About Ancient Populations (Autosomes versus just Y and mtDNA)

I don't think Neandertals died out at all.
 
No more so than any population that existed from 600,000 to 25,000 years ago.
 
If you tested ANY species of Homo that old, of course they wouldn't match us exactly. The genus has evolved.

Neandertal population size was tiny. Imagine that there were 40,000 of them in Europe. (That number is actually large.  Many aDNA experts believe that there were never more than 10,000 Neanderthals alive at any one time!)

Now imagine that 1 million modern humans come into Europe, during various phases.
 
You mix them together, and you get the 4% of Neandertal autosomes in our populations.

You also get drastically smaller odds that their sex-linked DNA survives over time.

Never, ever forget population size.

This "study" has been replicated in modern times.
 
Imagine 100 men are marooned on an island. 4 have the surname "Rarityrareness."

After generations, it is likely that the sons of those 4 will have a generation or two that produces only daughters. In fact, it's almost certain.

So the odds are that there will be no Y chromosomes of the Rarityrareness males.

But did they survive? Yes. Their descendants through their daughters are very much alive in the population.  And like Neandertals, large percentages of their genome would survive autosomally, perhaps as high as 80%!

Never ever forget initial and comparable population size. It explains just about every ratio of the newer versus older Y Chromosomes in Europe. 

It explains the lack of Neandertal sex-linked DNA, and it explains the smaller number of the Old Europe haplogroups from small hunter-gatherer populations.