New Delhi, Oct. 14 -- In 1960, at Gombe in Tanzania, Jane Goodall watched a chimpanzee strip the leaves from a twig, push it into a termite mound and draw it out crawling with insects. She wrote to her mentor Louis Leakey, who is said to have replied that we must now redefine 'tool' or redefine 'man' or accept chimpanzees as human. Tool-making was supposed to separate us from every other creature. In one afternoon, it was gone.

It is worth asking how that separation line came to be drawn so firmly. The 20th-century study of animal minds began with a sound instinct: do not credit an animal with sophisticated thought when a simpler explanation will do.

That is good method. But good methods have a way of hardening into doctrine. Caution be...