An international team of researchers from the Max Planck Institute of Geoanthropology in Jena has set side by side three sets of data: models of the distribution of the largest complexes of vector mosquitoes, palaeoclimatic models and the settlement sites

An international team of researchers from the Max Planck Institute of Geoanthropology in Jena has set side by side three sets of data: models of the distribution of the largest complexes of vector mosquitoes, palaeoclimatic models and the settlement sites of early humans in sub-Saharan Africa in the period from 5,000 to 74,000 years ago. The result is a map showing how human populations consistently avoided, or died out in, precisely those zones where malaria caused by Plasmodium falciparum was likely.

This factor shaped human demography over the last 74,000 years, and probably for a good deal longer

says Andrea Manica of the University of Cambridge.

By fragmenting human societies across the landscape, malaria helped to create the population structure that we observe today.

The standard model of the dispersal of Homo sapiens rested on two factors: climate and physical barriers such as mountains, deserts and seas. Naturally, however, many disciplines and studies lay claim to adding one more critical factor affecting the settlement of the earth. Besides mosquitoes, it may be parasites, epidemics, radiation, geomorphological processes and so on. It is important to understand that there is no single factor that drove humankind onto this or that land; it was always a strange and intricate complex of causes, naturally not fully grasped by the populations themselves.

Nevertheless, the genetic diversity of modern African populations, their geographical differentiation, and the presence or absence of a number of adaptations correlate handsomely with the "malarial" factor. Sickle-cell anaemia, which gives partial protection against malaria, is the best-known example of such an adaptation.