Take smoking. In the 1950s, researchers started to investigate the
massive rise in lung cancer deaths that had occurred during the
preceding decades.[38] There seemed to be a clear link with the
popularity of cigarettes: people who smoked were nine times more
likely to die of the disease than non-smokers. The problem was how
to show that smoking was actually causing cancer. Ronald Fisher, a
prominent statistician (and heavy pipe smoker) argued that just
because the two things were correlated, it didn’t mean one was
causing the other. Perhaps smokers had very different lifestyles to
non-smokers, and it was one of these differences, rather than
smoking, that was causing the deaths? Or maybe there was some
genetic trait – as yet unidentified – that happened to make people
both more likely to develop lung cancer and more likely to smoke?
The issue divided the scientific community. Some, like Fisher, argued
that the patterns linking smoking and cancer were just a coincidence.
Others, like epidemiologist Austin Bradford Hill, thought that smoking
was to blame for the rising deaths.
Of course, there was an experiment that would have given a
definitive answer, but as we’ve already seen, it wouldn’t have been
ethical to run it. Just as modern social scientists can’t make people
take up smoking to see if the habit spreads, researchers in the 1950s
couldn’t ask people to smoke to find out if it caused cancer. To solve
the puzzle, epidemiologists had to find a way to work out whether one
thing causes another without running an experiment.
R 1898 waiting to announce his discovery
that mosquitoes transmitted malaria. While he battled to get
government permission to publish the work in a scientific journal, he
feared others would pounce on his research and take the credit.
‘Pirates lay in the offing ready to board me,’ as he put it.[39]
The pirate he feared most was a German biologist named Robert
Koch. Stories were circulating that Koch had travelled to Italy to study
malaria. If he managed to infect a person with the parasite, it could
overshadow Ross’s work, which had used only birds. Relief came a
few weeks later, in the form of a letter from Patrick Manson. ‘I hear