In the distant future, humans are on the verge of extinction and have settled in small tribes across the planet under the observation and care of "Mothers." Some children are made in factories, from cells of rabbits and dolphins; some live by getting nutrients from water and light, like plants. The survival of the race depends on the interbreeding of these and other alien beings--but it is far from certain that connection, love, reproduction, and evolution will persist among the inhabitants of this faltering new world.