Selsam at her best--which is to say, natural history as it should be presented to children. First, interest is aroused by the volcanic islands' dramatic origin and highly peculiar assortment of spectacular flora and fauna. (There are flightless and night Hying birds, spiny sea lizards and prickly pear cacti 30 feet high, an equatorial penguin, and the famous giant tortoises that Darwin said looked like ""huge rocks taking a walk."") Next, Selsam asks the very questions--how did they get there? why so few mammals? why the sharp differences from one island to the next?--that her canny briefing has induced you to ponder. Only then does she come up with the answers--some of them still tentative and incomplete. And, in the process (no awkward background digressions here), she answers questions about evolution that you didn't know you had. Crisp and intelligent--and the photos are knockouts.