I wrote yesterday on the new research by Collard et al. that suggests that Britain experimented a rapid population increase in the few centuries that followed the arrival of farming to the island. Afterwards a reader has sent me a copy of the paper (a million thanks again) and I can now comment a bit further with better knowledge of the matter.
But first of all the sequence:
This graph, which is central to the research, represents the archaeological findings with a C14 date for the whole island of Great Britain (I understand). As you can see the population explodes after c. 6000 calBP (calibrated C14 dates, our best equivalent to "years ago" since 1950 - equivalent to c. 3950 BCE in this case), even if we discard the monuments. The demic growth was some 400% in four centuries, maybe more.
Later, by the second half of the millennium, the population decreased very sharply again but, thanks to agriculture surely, remained higher than in the Epipaleolithic (250%?). Since then it remained stable, although it is difficult to interpret the growth in monumental sites in the second half of the 3rd millennium BCE in terms of demography.
As the authors argue this explosion is difficult to conciliate with a process of gradual incorporation of farming by the natives and fits best with the model of colonization from the mainland.
Most of the Neolithic colonization (or demic explosion) process happened in two specific areas: SW England and central Scotland. The rest of the island was unaffected or only affected in a secondary and less intense manner. Naturally (climate) SW England experienced a much more intense demic explosion than Scotland, which began slightly before and ended also somewhat later.
This is the situation at the apogee of SW English Neolithic, 5600-5700 calBP ("hotter" colors like white imply greater density, black implies same density as in Epipaleolithic):
The Scottish Neolithic apogee was apparently some 100 years early and here is shown already receding (but was not much more extense nor intense anyhow).
Armorican ('French') origins
The authors argue that the migrations were two, both originated in NW France but in different subregions.
The first wave was that affecting SW England and seems to have originated in the Megalithic area of Lower Normandy, with some elements also from the (non-Megalithic) Neolithic of Nord-Pas-de-Calais.
One hundred years later more or less, a second wave original from Brittany (also within the Dolmenic Megalithism cultural area) touched in coastal Wales and reached Scotland. There are no traces of any other migration.
Both Lower Normandy and Brittany, as well as the inland areas between the Seine and the Loire rivers, were a homogeneous cultural region that is only second in Europe to develop the Dolmenic Megalithic cultural set (earliest known are in Southern Portugal and nearby districts of Spain, soon after Neolithization, c. 7000 BP). In Celtic and Roman times it was known as Armorica, meaning the Sea Country, as a whole it has no other collective name so guess that talking of Armorican Neolithic or Armorican Megalithism makes full sense.
This ancient country would be in any case the main source of the Neolithic colonists that this paper suggests.
Why did the population decline so sharply after the initial explosion? Did they over-exploit their environment? Is the initial abrupt growth an artifact of archaeological research?
If the arrival of Neolithic to Great Britain (and NW Iberia at least) is product of the spread of Dolmenic Megalithism, does this imply that we should begin to consider Megalithic expansion as a demic phenomenon in general, with all the implications it would have in population genetics? I find this hard to believe but I am not totally sure. If so, should we consider Portugal as the origin?
What happened in the "black" (or even dark red) areas that are about half of the island? It does not look like there was any colonization there. How did they become Megalithic then?
Why did the people of Great Britain began building so many monuments since 2500 BCE? This is precisely a very hot period in Europe, when Indoeuropeans (Kurgan) took over West Germany and Scandinavia, but also just after the formation of the first West European civilizations in southern Iberia (VNSP and Los Millares) and not long before the increase in trade associated to the Bell-Beaker phenomenon. Does all this imply some sort of increase in political organization?
Source: Mark Collard et al., Radiocarbon evidence indicates that migrants introduced farming to Britain. Antiquity, 2009.