Can this reflect an elite population having a decline in birth rate as it stabilizes, the upper class women choosing not to have every baby that came their way, while at the same time the population of a subsumed ancient group that survives as a lower class also stabilizes but doesn’t have the option to limit their birthrate?

And it is not just me thinking this way! I just blogged about the genetic and isotope study of migrants from the steppe currently under way. The results won’t be available until 2012 at the earliest. But an overview in a German-language magazine in February shows the thinking: Invasion aus der steppe.

Given that in many historical examples where we know what happened, or have very definitive population DNA evidence, the proportion of indigenous NRY-DNA is smaller because to inmigrating population is male dominated and/or integrates more local women than men into its population, but there are very few, if any, examples of female dominated migrations, the 15% figure for indigenous ancestry from the mtDNA is probably a cap rather than a floor on the percentage of the Western European genome that could be from an indigeneous source.

The overall percentage of European hunter-gatherer ancestry could easily be in the 9% to 12% range.

The low portion of European hunter-gatherer ancestry may also help explain why modern European, in the former range of the Neanderthals, do not have an elevated level of Neanderthal admixture.

Neolithic immigrants from Anatolia, the Balkans or the Near East would have only the level of Neanderthal admixture found in all Eurasians, after which contact with Neanderthal populations would have ceased as the Neanderthal range retreated. The only population to have prolonged contact with Neanderthals were the European hunter-gatherers of the Paleolithic who may have co-existed with Neanderthals at the fringe of their population for many thousands of years more than other modern humans. And, indeed, the particularly robust modern human skeletons that could indicate admixture with Neanderthals are found in Europe.

But, the excess Neanderthal admixture in the hunter-gatherer proportion would have been reduced by a factor of six or more during the Neolithic, and might have been reduced further already at that point if people from outside the group of descendants of the pre-LGM hunter-gatherers of Europe participated in Northern Europe’s resettlement from refugia as ice sheets retreated after the LGM.

Also, since more Neanderthal admixed hunter-gather descendants may have looked more different from Neolithic migrants into Europe than those who were less Neanderthal admixed, it is possible that they may have been adverse sexual selection against them into the more rapidly growing populations of farmers.

Since the amount of Neanderthal admixture into modern humans isn’t known very exactly (1%-4% is the current range), even a population of European hunter-gatherers with an 8-10% Neanderthal admixture percentage wouldn’t have made a distinguishable dent, given the accuracy of the methods that have been used so far, in the Neanderthal admixture percentage of current European populations.

I agree entirely, but

So, the vast majority of the ancestry of modern Europeans can be traced back to farming cultures of the eastern Mediterranean which swept over the west of Eurasia between 10 and 5 thousand years before [the present]

ignores Indo-European migration from the steppe c. 5000 BP.

The mtDNA haplogroups selected to represent the Upper Paleolithic were U5, V, and H3. Those selected to represent the spread of agriculture were T1, T2, J1a, K2a. (They threw in H4, but that has not been solidly linked to the Neolithic, and they made the calculations with and without it, reporting no difference.)

Haplogroup H represents nearly half the modern European population. As Barbara Bramanti et al (2009) pointed out in a rather puzzled way, the genetic make-up of modern Europe cannot be explain solely by adding the hapologroups found in actual Mesolithic DNA to the hapologroups found in Neolithic DNA. Something (another migration?) must have happened later.

The stabilisation of the Neolithic haplogroups on their graph about 4000 BP does not reflect population growth just stopping. It didn’t stop. The current population of Europe is vastly greater than it was 4000 years ago. What we see after that is an otherwise unaccountable rise in the haplogroups more ancient in Europe (including the European steppe), plus other younger haplogroups that they didn’t include in the study, like H5a. H5* is most frequent and diverse in the western Caucasus and may have spread from there, while H5a has a stronger European distribution. H5a is thought to be only 7000-8000 years old, so its wide, though low, spread over Europe suggests that significant migration took place even after the initial spread of farming.

I reported on this paper on my blog also (before Dienekes) : http://dna-forums.org/index.php?/blog/2/entry-143-neolithic-population-growth-estimated-from-mtdna/
Edited.