Question: Hi Julian. Following on from my last question: (http://ias.im/30.259) about the malaria parasite and blood type immunity do you believe that in the future people's natural genetics and natural immunity will become sufficient, through the process of evolution by natural selection, as to become immune to the parasite’s effects, as has happened in the case of the Plasmodium vivax? Or do you believe that the genus classification will continue to expand so that there are more and more species of malaria parasites, each mutated, as a predator-prey relationship to feed on humans, meaning that we will never be free of the malaria epidemic. In short, do you think that we would have reduced malaria cases purely through evolution, and eventually that the entire malaria parasite would have become extinct, as is possible now with the aid of modern medicine (which is continuing to develop and improve all of the time)? Thanks again, Andrew

Julian Rayner answered on 15 Mar 2011:

Hi Andrew

Great question! Man, some serious research behind that one. The problem with evolution is that it works on long long time scales. Think of the generation time of humans – let’s say 20-30 years. If a genetic change had a slight selective advantage, in that it protects some people against malaria, it would only increase in frequency a bit every 20-30 years. If it had a massive advantage, like Duffy negativity must have had, it would spread faster, but even then would probably take several thousand years before enough people had it to make a big difference. There are also odd things about how evolution works – chance plays a big role. Why did people in Asia, where there are hundreds of millions of cases of P. vivax each year, not evolve Duffy negativity? Because evolution doesn’t always work in a directed, logical way.

Your point about parasites evolving back and the predator-prey relationship is a great one too. There was a paper recently about P. vivax in Duffy negative people in Madagascar, which is not supposed to be possible. We don’t know what is going on yet, but it is possible that some strains of P. vivax are evolving a way around Duffy negativity.

In short, our best crack at eradicating malaria comes with modern medicine and better healthcare in the developing world. It’s a formidable problem though.

Julian.