Simulation and Separation by Principal Components of Multiple Demic Expansions in Europe

Abstract

The spread over Europe of populations coming from different places at different times has been simulated with the main purpose of testing the possibility of separating independent migrations by the multivariate technique of principal components already used by Menozzi et al. (1978) in their analysis of actual gene frequencies in Europe. Demographic parameters, however partial and unsatisfactory, are introduced and discussed for the pre-agricultural situation and the Neolithic agricultural expansion. Other expansions have been simulated by using the same general model set up for agricultural diffusion but with substantial changes in the parameters, with the following results. 1. Migration and growth of populations similar to those found in the few known ethnographic situations are compatible with the actual rate of diffusion of agriculture during the Neolithic. 2. The rate of acculturation and the increase in population size allowed by new cultural innovations are critical factors in determining the patterns in the geographic distribution of genes and their clines. 3. Independent demic diffusions can be differentiated by analyzing the principal components of a set of geographically structured gene frequencies. 4. When the diffusion of people has reached its saturation limits, the genetic gradients thus generated become almost frozen and change only slowly thereafter. The leveling-off of a genetic cline by migration in the absence of selection can be extremely slow if the rate of migration constant over time.