INTELLIGENCE IS a slippery concept, even in our own species, tricky to define and tricky to measure. One psychologist describes it as “the capacity to learn or to profit by experience.” And another, as “the capacity to acquire capacity”—the same sort of circular definition offered up by Harvard psychologist Edwin Boring: “Intelligence is what is measured by intelligence tests.” As Robert Sternberg, a former dean at Tufts University, once quipped, “There seem to be almost as many definitions of intelligence as . . . experts asked to define it.”
