Pinker criticizes a number of common ideas about language, for example that children must be taught to use it, that most people's grammar is poor, that the quality of language is steadily declining, that the kind of linguistic facilities that a language provides (for example, some languages have words to describe light and dark, but no words for colors) has a heavy influence on a person's possible range of thoughts (the Sapir–Whorf hypothesis), and that nonhuman animals have been taught language (see Great ape language). Pinker sees language as an ability unique to humans, produced by evolution to solve the specific problem of communication among social hunter-gatherers. He compares language to other species' specialized adaptations such as spiders' web-weaving or beavers' dam-building behavior, calling all three "instincts".