Darwinian medicine warns us not to wipe out depression-it may serve a purposeby Geoff Watts / August 20, 1997 / Leave a comment
As a teenager I suffered from hay fever, but not from rabbit’s tic or neuralgia rosa. Why? Because only the first of these is a real disorder; the others are pure invention. In principle, though, they too could exist. We know how pollen triggers the cells of the hay fever sufferer’s immune system into releasing a flood of histamine, the cause of all the undignified misery. It would not be hard to dream up some physiologically plausible chain of events to explain, say, why hearing a pure tone of a particular frequency might trigger a nervous twitch of the muscles around the nose (my rabbit’s tic); or why prolonged exposure to intense red light could be followed by a sharp pain at the front of the skull (the imaginary neuralgia rosa). A priori such disorders are no more improbable than postulating a violent sneeze in response to sniffing certain types of pollen (hay fever); they just happen not to exist. How arbitrary are the ills to which flesh is heir.
Or are they? The Darwinian approach to an already lengthy list of ailments has revealed that bodily failures are anything but arbitrary. The many varieties of human disease are turning out to fit a pattern as sweet as the tidiest mind could hope for. My own first insight into what is now called Darwinian or evolutionary medicine came more than 20 years ago. I was at a conference in Davos organised by a drug company to celebrate an asthma product of which the firm’s medical director was proud. In keeping with the “educational” nature of the event, much of the proceedings had nothing to do with the drug-including one paper which became, for me, the highlight of the event.
Its authors set out to explain why there is such a thing as hay fever. They explained that this and most other forms of allergy are the minor drawbacks of a branch of the immune system which originally protected us against parasitic worms. Throughout our evolution, such worms must have been ubiquitous, and seriously damaging to health. Natural selection would therefore have favoured the emergence of effective defences against them. The drawbacks of a system sensitive enough to be triggered from time to time by things which are not parasites (pollen, strawberries and so on) would have been outweighed-so the argument goes-by the advantages of a guaranteed response when the genuine…