Graphic representation of the impact of malaria on the formation of the human niche
© Michela Leonardi
A powerful and predictable result of an arms race between a host and a parasite is that the host population will evolve in ways that make it better able either to resist the parasite or to survive despite its presence. In other words, the presence of a parasite can be a strong environmental selector and a major driver of evolutionary change. And, of course, parasite-host arms races make no sense in terms of intelligent design, still less when the designer is supposed to be omnibenevolent.
One well-known example of this evolutionary pressure is the persistence of the sickle-cell allele in parts of the world where malaria is, or has been, common. Carrying one copy of the sickle-cell mutation provides a degree of protection against the malaria parasite, Plasmodium falciparum. Carrying two copies, however, causes sickle-cell disease, which can be severely debilitating and sometimes fatal. The result is a classic example of balancing selection: in malarial regions the allele can be maintained in the population, despite its harmful effects in those who inherit two copies, while in populations not exposed to malaria it tends not to persist at high frequency.
Now scientists from the Max Planck Institute of Geoanthropology and the University of Cambridge, with colleagues, believe they have shown that Plasmodium falciparum malaria was a significant factor in the deep history of Homo sapiens in Africa. Their study suggests that malaria helped shape where early human populations could live between about 74,000 and 5,000 years ago, fragmenting populations across the landscape and influencing patterns of contact, separation and genetic exchange long before recorded history. This was the crucial period before humans dispersed widely beyond Africa and before agriculture dramatically altered patterns of malaria transmission.
They have recently published their findings, open access, in the journal Science Advances.
The irony, of course, is that this study shows modern humans not as the product of an intelligent designer’s magic, but as the outcome of deep evolutionary history, shaped in part by parasite-host arms races — one of the strongest arguments against any intelligent, benevolent agency being involved in the process.



































