Is Mankind the Crown of Creation? Or must we concede pride of place to the bottlenose dolphin and the sperm whale? Dr. Fichtelius, a Swede who has spent five years trying to communicate with dolphins, suggests that they may well be our superiors in intelligence and adaptability to their environment, the briny deep. By this time everyone knows what endearing creatures they are -- playful, utterly lacking in aggression and seemingly full of tender emotions -- ""like human beings, dolphins can develop ulcers from grief."" But did you know that a dolphin's brain weighs 1,700 grams while a human makes do with a paltry 1,4007 Or that comparative anatomy of the cerebral cortex shows that the dolphins' limbic system is superior to that of homo sapiens and consequently their behavior is probably more rational (""governed less by emotion and more by reason"") than ours? Mind you, the authors are not didactic about the dolphin's mental capacities; the chief aim seems to be to take man down a peg or two, to question his hopelessly anthropocentric picture of the world. Perhaps through the study of other large-brained mammals -- including elephants and chimps -- humankind will come to understand that the earth ""was not created for us to play with, or consume, or vandalize."" But though they tend to moralize excessively at times, the authors do provide a good deal of really fascinating information on the whales' sonar orientation, large acoustical memory bank, vocalizations and ""spontaneous tameness"" in captivity. Like John C. Lilly (The Mind of the Dolphin, 1967), the authors are extremely optimistic about the dolphin's linguistic potential though ""we will have to take the first steps toward eventual communication"" with our aquatic brethren. They're also somewhat pessimistic about our potential to deal with nuclear war, famine, pollution and other environmental hazards. ""It has happened before that a dominant species has vanished from the face of the earth,"" so please -- a little more respect for them that may become our heirs.