It helps to be sick

Being sick helps you survive says Sharon Moalem, author of Survival of the Sickest. A condition where the body stores a lot of iron may have led to the the survival of a large number of people after the years of Black Death, the author describes in a New Scientist article.

"Iron overload was once thought a very rare condition - a medical curiosity. But since the first genetic mutations for haemochromatosis were discovered in 1996, it has turned out to be much more common than we realised among those whose ancestors come from north or west Europe. The current estimate is that 1 in 200 of this population may have iron overload, but the real figure may be much higher as doctors do not often do the requisite tests and may put the symptoms down to other causes. When patients do get diagnosed, a surprising number turn out to have been conscientious blood donors, having unwittingly found a remedy for their aches and pains.

The most surprising finding, though, was that the number of people who carry a single haemochromatosis mutation and usually have just slightly raised iron levels is as high as 1 in 3 in some parts of Europe. Why are so many people walking around with these mutations, and why only in this part of the world?

My colleagues and I have developed a theory that iron overload mutations must have conferred some kind of benefit in our recent evolutionary past (Medical Hypotheses, vol 59, p 325). We believe the mutations may have been shaped by the most awesome selective force the European population has faced in recent history - the Black Death." - New Scientist article (subscription needed)