Darwin and the Study of Animal Intelligence
Charles Darwin's theory of evolution by natural selection (Darwin, 1859, 1871) had an enormous impact on •psychology as well as biology. Darwin argued that humans and other species share a remote common ancestor. This idea implied that each species has specializations adapted to its own way of life but also that all vertebrate species have many features in common. It further implied that nonhuman animals should exhibit varying degrees of human characteristics, including intelligence.
Based on this last implication, early comparative psychologists, specialists who compare different animal species, did something that seemed more reasonable then than it does now: They set out to measure animal intelligence. They apparently imagined that they could rankorder animals from the smartest to the dullest. Toward that goal, they set various species to such tasks as the delayed-response problem and the detour problem. In the delayed-response problem, an animal sees or hears a signal indicating where it can find food. Then the signal ends, and the animal is restrained for a delay to see how long it remembers the signal (Figure 1.7). In the detour problem, an animal is separated from food by a barrier to see whether it takes a detour away from the food to reach it (Figure 1.8).