The Rational Optimist (P.S.)

by Matt Ridley

As the average age of a country’s population rises, so people get more and more neophobic and gloomy.

As the evolutionary biologist Paul Ewald has long argued, viruses undergo natural selection as well as mutation once established in a new species of host and casually transmitted viruses like flu replicate more successfully if they cause mild disease, so that the host keeps moving about and meeting new people. A victim lying in a darkened room alone is not as much use to the virus as somebody who feels just well enough to struggle into work coughing. The modern way of life, with lots of travel but also rather more personal space, tends to encourage mild, casual-contact viruses that need their victims to be healthy enough to meet fresh targets fleetingly. It is no accident that modern people suffer from more than 200 kinds of cold, the supreme viral exploiters of the modern world. If this is so, why then did H1N1 flu kill perhaps fifty million people in 1918? Ewald and others think the explanation lies in the trenches of the First World War. So many wounded soldiers, in such crowded conditions, provided a habitat ideally suited to more virulent behaviour by the virus: people could pass on the virus while dying.