by employing innate genetic differences between people—an inborn susceptibility to alcohol, say, or to higher cholesterol levels in the arteries—they can now mimic, at much less effort and expense, the kinds of large trials that would be necessary to determine if an HDL-lowering medicine is really beneficial. The new technique, called Mendelian randomization, is already being used by drug companies to make billion-dollar decisions about which drugs to pursue. What may worry Davey Smith and others most is that as genetic databases have multiplied, tying genes to virtually any imaginable biological or even behavioral variable, studies of cause and association have become almost effortless.

The University of Bristol hosts a platform called MR-Base that lets anyone carry out virtual experiments without collecting any new data.

“You can do these studies now, sitting at your desk, in 10 minutes. It’s just too easy. Because of the flood of studies coming out, it may very well fall into disrepute.”

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