Frogs are not like us. They are better at catching flies but not, it seems, at explaining how they do it. The frog mind is narrowly specialized to control tasks such as locating small black specks, escaping predators, and finding mates, but not for reflecting on the ethics of eating insects or the issue of equal rights for toads.

This view of the limited intellectual capabilities of amphibians is unlikely to be controversial. If we extended it to apes the reaction might be different, and it would clearly be false of humans. How do we know? Because humans can tell us so and the others cannot. Although having a language is not a prerequisite for having a mind, language is overwhelmingly our best evidence for the nature of mind. Language is definitional of what it is to be human, and the study of language is a way in to the study of the human, but not the frog, mind.

Despite the complexity and variety of animal communication systems, no other creature has language like ours. Although chimpanzees and bonobos can be taught to manipulate an impressive array of signs and use them to communicate with us or with each other, human language, in particular the syntax of human language, is sui generis. As far as we know, even the singing of whales and the color communication of cuttlefish have nothing like (human) syntax. Surprisingly, the closest parallel with human language, more accurately speech, is found in birdsong. It is surprising because birds and humans are evolutionarily only remotely related, suggesting that the many shared properties of birdsong and speech are the result of convergent evolution rather than shared descent, although such analogic convergence may be controlled by the same genetic mechanisms, reflecting “deep homology.” In one respect our linguistic uniqueness is trivial: the inherent interest of our abilities would not be diminished just because it turned out that other species had even more in common with us than we had previously suspected.