麻豆传媒

THE great flu pandemic of 1918 killed, by some estimates, upwards of 100 million people worldwide. It might even have hastened the end of the first world war.

In the latest book on the great pandemic, Fever of War, historian Carol Byerly explores how the US military handled the flu. Astonishingly, the military historians of the time seem to have had an unspoken agreement to virtually ignore the impact of the pandemic. Other authors have made the same observation of civilian historians. Perhaps disease didn鈥檛 fit their idea of what kinds of events control history.

But the parallels between pandemic and war were not lost on everyone. Byerly cites two prominent military clinicians, one British and one American. Writing just after the war, they seem to have believed that the conflict and the flu were both 鈥渂iological phenomena鈥� of 鈥渦ndecipherable causation鈥�, and 鈥渂eyond the control of man鈥�.

You can see why they felt that way. If there was ever a war so pointless and brutal that it seemed beyond human control, it was the Great War. And the flu killed more people in a few months than the war did in four years. To these men, war and disease were huge, impersonal events that just happen, beyond anyone鈥檚 ability to understand or control.

Few would now describe either disease or war as an unstoppable force of nature. But could these two war-weary doctors have been intuitively onto something? Could the same natural laws that control the spread of diseases also control the spread and evolution of human ideas, and even of behaviours such as war? In ways neither could have guessed, some scientists now think this may be so.

In the June issue of PLoS Biology, Paul Ehrlich and Simon Levin of Stanford University in California have called for evolutionists, behavioural biologists and ecologists to start trying harder to model human cultural evolution. Useful models have so far eluded scientists. In particular, they say, we need to understand what controls the development of social 鈥渘orms鈥� which, among other things, govern war. The model they suggest is disease.

Richard Dawkins famously proposed the idea of the meme as a unit of cultural evolution, as the gene is for biological evolution. But Ehrlich and Levin say we have gained little understanding from trying to model memes as though they were genes. The two are just too different, they say: memes spread up, down and sideways in a population, not just from parent to offspring. They are impermanent. They vary enormously and quickly.

Yet that is exactly how pathogens behave. Like pathogens, ideas must infect a critical number of people before an epidemic starts. Some hosts are more susceptible than others. There are threshold phenomena, and superspreaders.

Similar ideas, Levin told me, were explored in The Tipping Point, writer Malcolm Gladwell鈥檚 bestseller of 2000, which used psychological research to show how fads and cultural norms spread much like disease 鈥� the 鈥渢ipping point鈥� being the critical threshold of some event that triggers an epidemic. All these ideas seem sensible enough to make you wish a hard-nosed experimental epidemiologist would get to grips with them.

Because if ideas can spread like epidemics, then epidemiological understanding may suggest controls. The idea of launching a war, for example, reaches its tipping point when it has infected enough of the right people. After that point, it can become unstoppable. Could there be some way of recognising where those epidemic thresholds are and interfering, by launching counter-ideas among the right people in the same way that doctors launch vaccine drives against disease?

But pursue the analogy. We have a vaccine against the kinds of viruses most likely to cause the next flu pandemic, but it seems unlikely that we will be able to administer it in time to make much difference. If we ever develop a war vaccine, who will administer it?