“Under conditions of random genetic drift and gene flow, what happens in a few generations may determine the general spatial pattern of gene frequencies for the next few hundred generations. Therefore, an environmental factor which is geographically variable within a species range, but acts only once or twice in a long time may be sufficient to maintain regional differentiation of gene frequences…This makes it extremely difficult to distinguish in practice between selection and genetic drift in cases of spatial differentiation…From the point of view of subspeciation and speciation, however, it is the larger differentiated areas which are of interest, and one would expect that most environmental factors would act more continuously” (p. 53)
– John A. Endler, “Geographic Variation, Speciation, and Clines” (1977). Monographs in Population Biology, Princeton University Press. ISBN: 9780691081922
As the role of technology in defining human ecology became more intense throughout the past two million years, it likely became a factor that acted in many ways parallel to what Endler describes above in talking about the role of environmental gradients. The use of technology (or culture more broadly) was varied across space and time and subject to non-continuous patterns of change. Just thinking aloud today….
