Dawn (The Xenogenesis Trilogy Book 1)
From the publisher: "Featuring strong and compelling characters and exploring complex themes of gender and species, Octavia E. Butler presents a powerful, postapocalyptic interplanetary epic, as well as a ray of hope for humanity. Lilith Iyapo has just lost her husband and son when atomic fire consumes Earth—the last stage of the planet's final war. An alien race calls on one woman to revive mankind after Earth’s apocalypse in this science fiction classic from the award-winning author of <em>Parable of the Sower</em>. They have kept Lilith and other survivors asleep for centuries, as they learned whatever they could about Earth. For the first time since the nuclear holocaust, Earth will be inhabited. Grass will grow, animals will run, and people will learn to survive the planet’s untamed wilderness. But their children will not be human. Not exactly."
In a world devastated by nuclear war with humanity on the edge of extinction, aliens finally make contact. They rescue those humans they can, keeping most survivors in suspended animation while the aliens begin the slow process of rehabilitating the planet. When Lilith Iyapo is “awakened”, she finds that she has been chosen to revive her fellow humans in small groups by first preparing them to meet the utterly terrifying aliens, then training them to survive on the wilderness that the planet has become. But the aliens cannot help humanity without altering it forever.