Even now nearly a quarter of all prescribed medicines are derived from just forty plants, with another 16 percent coming from animals or microbes, so there is a serious risk with every hectare of forest felled of losing medically vital possibilities. Using a method called combinatorial chemistry, chemists can generate forty thousand compounds at a time in labs, but these products are random and not uncommonly useless, whereas any natural molecule will have already passed what the Economist calls "the ultimate screening programme: over three and a half billion years of evolution."

Looking for the unknown isn't simply a matter of traveling to remote or distant places, however. In his book Life: An Unauthorised Biography, Richard Fortey notes how one ancient bacterium was found on the wall of a country pub "where men had urinated for generations" — a discovery that would seem to involve rare amounts of luckand devotion and possibly some other quality not specified.