Before human intervention the rules of disease were simpler. The competitors: pathogen vs. host. The rules: in order to win, the pathogen must ‘divide and conquer’, attacking the host’s defences and increasing in numbers; the host, on the other hand, must stay strong and defend hard in order to keep a united front, before finally striking back and wiping out the invaders. It was a game of risk, and the winner would ultimately find themselves stronger and better prepared for the next battle. This is because the hosts and pathogens necessarily need to coevolve – that is to adapt to each other simultaneously – in order to stay in the game. This concept was famously captured in a quote by the Red Queen in Lewis Carroll’s ‘Through the Looking-Glass’,
“Well, in our country,” said Alice, still panting a little, “you’d generally get to somewhere else — if you run very fast for a long time, as we’ve been doing.”
“A slow sort of country!” said the Queen. “Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!”
However, since modern medicine came along, the dynamics of the game have become more complex; and it is only recently that evolutionary biology has been considered a potential weapon against disease – by trying to predict and manipulate the pathogen’s strategies, in order to stay one move ahead. The application of evolutionary theory to understanding health and disease is known as evolutionary or Darwinian medicine – and it is being used to try and find answers for all sorts of medical ailments, such as: autoimmune diseases, diabetes, anxiety disorders, antibiotic resistance, and cancers (to name just a few). As such, Darwin – the “medical school dropout” – turns out to be having a bigger impact on the world of medicine than he could ever have imagined.