Is there only one possible outcome for the evolution of mankind? When
two cultures light years apart follow different evolutionary paths, that
question could be answered. And many more could be raised. In the
twenty-second century, Earth was dying. World population was more than
twenty billion, the global environment was in ruins, and living
conditions were intolerable everywhere on the planet. Many people
thought the only hope for mankind lay in colonizing space. And so giant
ships were built to carry brave volunteers who would settle the planets
of nearby stars. Many years later, the colonists returned. The Earth
they found was a far different place than the Earth of their distant
ancestors. And they were not welcome.