Malaria-protective alleles in southern Africa: relict alleles of no health significance

Summary

INTRODUCTION

The history of the evolution of malaria is not known with any degree of certainty. It is found among all the major groups of terrestrial vertebrates in the Old World, suggesting that the parasites predate the hominids by millions of years. It has been claimed that plasmodial species evolved in tropical Africa or else in South-East Asia. Bruce-Chwatt (1965) pointed out that there were references to malaria dating back to 2000 BC and Hippocrates writing in the 5th Century BC was well aware of malarial fevers. There are also references to malarial fevers in the literature of India, and one writer went so far as to attribute them to mosquitos.

Prior to the 3rd Century BC, the entire population of sub-Saharan Africa consisted of small bands of hunter–gatherers. Such a low population density, coupled with the fact that such people were not tied to settlements near water holes, probably meant that malaria was nowhere hyperendemic. But by about 250 BC the Nok culture made its appearance in what is now northern Nigeria but extending both west and east at the same latitude. This belt was then probably wetter and more thickly wooded than it is today even though it was still to the north of the high forest. It was suitable for cereal growing, and the transition of people from the Stone Age into the Iron Age is thought to have taken place in that region. With farming implements made from iron, the people could cut trees and till the soil more effectively, and expand into the forest areas.