As ecological dominants, humans attempt to control both their immediate predators and entire species that we consider pests. At Princeton, the Grants’ colleague Martin Taylor studies pesticide resistance in a certain species of moth. His work illustrates that “resistance movements” emerge consistently when the species is targeted for extermination; the same is true of house flies, bacteria, viruses, and game such as fish and elephants.

Each case tells a story in which an organism presents a problem for humans, such as the invasion of a cotton farm by Taylor’s moths. In response, humans attempt to kill the organism, using potent substances such as DDT or, in the case of bacteria, antibiotics. Failing to account for evolutionary theory, humans expect these poisons to work indefinitely, unprepared for the inevitable evolutionary response. Nature selects for characteristics in the pests that resist the poison. Resistance increases rapidly, and variably, and the task of destroying the pest becomes an elusive, fast-moving target.

In the case of insects, this process leads to pest populations that continue to destroy crops despite an onslaught of pesticides. In bacteria and viruses, which evolve much faster than we develop treatment, the pattern leaves us vulnerable to future epidemics.