Second in the Xenogenesis series (Dawn, not reviewed), from the talented author of Clay's Ark (1984), in which the alien Oankali have descended upon an Earth devastated by nuclear war. The Oankali, who look frightful but have vast biological talents, have rebuilt both the Earth's biosphere and the surviving humans--giving the humans long, healthy lives while withholding their ability to reproduce without the Oankali's aid. Why? Well, the much-traveled aliens make their living by collecting and interpreting genes--so they know that any nascent human civilization will inevitably destroy itself. Some humans cooperate with the Oankali (they have a third, neuter, sex, ooloi, that mediates reproduction) and produce ""construct"" offspring, fusions of human and Oankali. The uncooperative wild humans, unable to bear children, often try to kidnap the construct children despite their nonhuman attributes (sensory tentacles, indeterminate sex, a final repellent-looking metamorphosis, and so forth). The wild humans, then, pose a thorny problem for the kindly Oankali--so when Lilith's young construct son Akin is kidnapped, the Oankali refuse to rescue him (Akin is, however, self-reliant and mature far beyond his human age) in the hope that he will, by coming to understand the wild humans from an Oankali viewpoint, find a solution. Butler's spare, vivid prose style invites comparison with the likes of Kate Wilhelm and Ursula Le Guin. Add on the intriguing, well-developed ideas here, the solid characters and crisp narrative: Butler in top form.