There's a new paper on ancient DNA out, Targeted Retrieval and Analysis of Five Neandertal mtDNA Genomes:
Analysis of Neandertal DNA holds great potential for investigating the population history of this group of hominins, but progress has been limited due to the rarity of samples and damaged state of the DNA. We present a method of targeted ancient DNA sequence retrieval that greatly reduces sample destruction and sequencing demands and use this method to reconstruct the complete mitochondrial DNA (mtDNA) genomes of five Neandertals from across their geographic range. We find that mtDNA genetic diversity in Neandertals that lived 38,000 to 70,000 years ago was approximately one-third of that in contemporary modern humans. Together with analyses of mtDNA protein evolution, these data suggest that the long-term effective population size of Neandertals was smaller than that of modern humans and extant great apes.
The comparison with modern humans is interesting and informative: we're a rather homogeneous species with a small long term effective population size. This ratchets down how numerous Neandertals were to breeding populations on the order of 1,000-10,000 individuals. Seeing as how Neandertals ranged from Spain to Kazakhstan it seems that they were likely spread rather thin then.
Here's Nature's take:
The difference implies that between 38,000 and 70,000 years ago, Neanderthals lived in smaller, more isolated pockets. The team estimates that around 270 to 3,500 breeding females would have lived at any one time as part of a total population that would have included their families and non-breeding Neanderthals. The team's estimate of the number of breeding females is in a similar range to a previous estimate that was based on a single Neanderthal genome3.But anthropologist Anna Degioanni at the University of the Mediterranean in Marseilles, France, notes that the region of mtDNA the Briggs group studied does not vary as much as other regions, such as the one her group used to identify different subgroups of Neanderthals earlier this year4. That may mean that the new study underestimates the genetic diversity of Neanderthals, she believes.
Both Degioanni and Briggs expect that future studies of nuclear DNA, which is more complex and contains more potential variations, will help settle the diversity question more definitively.
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I wonder how much of this population size difference is because the Neandertals had a smaller habitible range (Africa is like 3 times larger than Europe+Levant, though only a subset of each continental area will be habitible) and how much is due to lower population density within that range.
Really interesting stuff.
As a non-scientist semi-informed layman who merely has a long interest in our understanding of human origins, it seems that most everything I read about archaic humans or protohumans (is that a technical term? I don' know) like erectus and the natural history of pleistocene eurasia with their presumed abundant natural populations of migrating prey animals covering the great grasslands that were so prevalent then, suggest to me a wide ranging kind of lifestyle across a pretty big territory, going after the passing herds and other seasonal occurances of abundance, naturally, expanding as opportunity or need arose, it doesn't seem to hard to imagine continental distances being crossed in only a few generations even if they didn't fully populate as they went. The fact that certain areas with limestone caves preserve bones better than most other environments skews our perceptions and interpretations of what their lifestyles and maybe their geographical ranges actually were at their fullest extent, I think.
And in my periphery, I wonder what sort of story was taking place at that same time along coastal migration-ways now well below sealevel from 2mya. This means evidence is scant but it almost hard to imagine coastal travel not being a major factor in population movement, even without boats..and what better or more bountiful ecosystem is there than the ocean's coasts, it seems like it would have been the best first place (at least back then)for a resource seeking social creature, with the tools and aggressive capabilities like the ancestors are thought to have had, I think they would make the seal/bird/shellfish/turtle/crustacean/salmon rich edge of the sea their preferred habitat if they could.
So this interpretation of the evidence is appealling to me and fits well with what my reading tells me it might have been like, with a healthy dose of pure speculation.