Francine ""Penny"" Patterson, who earned her psychology doctorate at Stanford with ""Project Koko,"" has been working and signing (in Ameslan, the sign language of the deaf) with her female gorilla since obtaining the then-infant in 1971. Though other such experiments have been with chimps, Patterson believes (and seems to demonstrate) that the gorilla's less cooperative nature accounts for our traditional underestimation of its relative intelligence. Patterson doesn't claim that gorillas are potentially as smart as people, but Koko has convinced her that they are capable of language--and she argues persuasively that Koko can understand symbols, ask questions, make jokes, comment as a spectator, and lie ingeniously. At times, though, critics might suspect that Patterson sees examples of metaphor, humor, or defiance in just plain wrong answers. It's not clear, either, that Koko attributes the meaning we do to the abstractions she uses so glibly. And Patterson doesn't claim that Koko understands and generates complex grammatical structures, the criterion for language to which skeptics of ape ability have retreated since chimps pushed back the earlier barriers. Rather, Patterson maintains that in place of word order, Koko substitutes inflections and modulations. One suspects that Patterson--unlike Herbert Terrace who subjected ape language to rigorous questioning in his own account of teaching Nim (1979)--will leave both supporters and skeptics about where she found them. However, her careful structure, favorable conditions, exemplary record-keeping, and intelligent exposition make her study a major document in the debate. Her rapport with Koko and, one suspects, the contributions of co-author Linden, make this an engagingly readable report as well.