Carl Sagan
Two billion years ago our ancestors were microbes; a half-billion years ago, fish; a hundred million years ago, something like mice; ten million years ago, arboreal apes; and a million years ago, proto-humans puzzling out the taming of fire. Our evolutionary lineage is marked by mastery of change. In our time, the pace is quickening. When we first venture to a near-Earth asteroid, we will have entered a habitat that may engage our species forever. The first voyage of men and women to Mars is the key step in transforming us into a multiplanet species. These events are as momentous as the colonization of the land by our amphibian ancestors and the descent from the trees by our primate ancestors. Fish with rudimentary lungs and fins slightly adapted for walking must have died in great numbers before establishing a permanent foothold on the land. As the forests slowly receded, our upright apelike forebears often scurried back into the trees, fleeing the predators that stalked the savannahs. The transitions were painful, took millions of years, and were imperceptible to those involved. In our case the transition occupies only a few generations, and with only a handful of lives lost. The pace is so swift that we are still barely able to grasp what is happening. Once the first children are born off Earth; once we have bases and homesteads on asteroids, comets, moons, and planets; once we’re living off the land and bringing up new generations on other worlds, something will have changed forever in human history. But inhabiting other worlds does not imply abandoning this one, any more than the evolution of amphibians meant the end of fish. For a very long time only a small fraction of us will be out there.
more…