Environment and human populations in Palaeolithic and post-Palaeolithic times : two models of adaptation

Palaeolithic populations displayed a strong morphological differentiation. The average biological distance between groups from Europe is much more higher in the Palaeolithic than in subsequent periods. Palaeolithic populations differ from post‑Palaeolithic ones on mortality structure, fertility structure, population size and density, biological state and dynamics etc., and also on response intensity to various environmental and cultural factors, i.e. the level of adaptability reactions (ecosensitive ones).

A great deal of anthropological papers showed biological consequences of “Neolithic revolution”. Research objects were chiefly characteristics displaying a high level of reactions to ecological (environmental) factors such as nutrition, diseases, climate, soil composition etc. Individuals’ responses to agents altering phenotypic formation of morphological traits were mainly analysed. Relatively few works concerned to the role of natural selection in morphological variability formation of Palaeolithic and post‑Palaeolithic populations.

The paper deals with an estimation of opportunity for natural selection operating by differential mortality and differentiating fertility (differential reproduction) in Palaeolithic and post‑Palaeolithic populations. On the ground of palaeodemographical and biodemographical data analysis of modern hunter‑gatherers and agriculturalists’ groups and morphological data it was shown, that in Palaeolithic differential death‑rate (if occured: indirect evidence is an occurrence of a strong races origination process), particularly in the reproductive period, could be the main field of natural selection activity. In post‑Palaeolithic populations severe decline of mortality is not observed, but rather intensification of this process in the first phase of neolithisation. At the same time processes of races origination are subject to diminution. Rapid increase of Neolithic populations density as in subsequent periods suggests considerable increase of fertility. We consider that just differential fertility and differential reproduction should be the field of natural selection activity in these populations.

Differentiated mortality in reproductive period in Palaeolithic could be an effect of the following factors: change of ecological zone; radical alteration in occupied ecological zone caused (through differential mortality: fertility was relatively low, by the way) changes in biological state of population; intensification of morphological structure. Distinctions between groups inhabiting various ecological zones, what for Palaeolithic populations are the main factors have well‑defined adaptive significance.

In post‑Palaeolithic populations change in populations density and structures caused differences in selective pressure on the natural selection, so differentiation appeared anew. Different “ways” of these populations’ development in these ecological conditions, after certain period of stabilisation of their adaptive structure (population size and dynamics), caused changes in phenotypic structure of morphological traits and created new morphological distinctions of regional level.

The morphological structure of Palaeolithic populations is the result of: 1) the adaptation to their ecological conditions, as the response of natural selection, 2) the rearrangement of basic traits in situation of scarce population density, and 3) a great fertility in reproductive period.

In the initial stage of the population density increase there was an effect of post‑Palaeolithic populations with distinctive morphological structure formed by natural selection. In stabilisation period effects of natural selection were of minor importance. In this stage morphological distinctions become the result of their ecological and social conditions.

During Neolithic and post‑Neolithic times population density increased and post‑Neolithic groups represent that previously autochthonic (in adaptive morphological features “lost” their differentiation) but in changed conditions new cultural equipment of nutrients adapt the population being under different selective pressure. Common adaptive structure, new morphological processes were mutually independent. Palaeolithic “racial” distinctions became an essential adaptive distinction, so morphological processes of natural reduction (body size reduction, gracilisation, sexual dimorphism etc.) increased.