Cosmic Connection by Carl Sagan Read Free Book Online Page A

temperature which he enjoys upon the Earth, could not, according to all appearance, live upon the other planets; but ought there not to be a diversity of organization suited to the various temperatures of the globes of this universe? If the difference of elements and climates alone causes such variety in the production of the Earth, how infinitely diversified must be the production of the planets and their satellites?” Laplace wrote these words near the end of the eighteenth century.
    The virtue of thinking about life elsewhere is that it forces us to stretch our imaginations. Can we think of alternative solutions to biological problems already solved in one particular way on Earth? For example, the wheel is a comparatively recent invention on the planet Earth. It seems to have been invented in the ancient Near East less than ten thousand years ago. In fact, the high civilizations of MesoAmerica, the Aztecs and the Mayas, never employed the wheel, except for children’s toys. Biology–the evolutionary process–has never invented the wheel, in spite of the fact that its selective advantages are manifest. Why are there no wheeled spiders or goats or elephants rolling along the highways? The answer is clearly that, until recently, there were no highways. Wheels are of use only when there are surfaces to roll on. Since the planet Earth is a heterogeneous, bumpy place with few long, smooth areas, there was no advantage to evolving the wheel. We can very well imagine another planet with enormous long stretches of smooth lava fields in which wheeled organisms are abundant. The late Dutch artist M. C. Escher designed a salamander-like organism that would do very well in such an environment.
    The evolution of life on Earth is a product of random events, chance mutations, and individually unlikely steps; small differences early in the evolution of life have a profound significance later in the evolution of life. Were we to start the Earth over again and let only random factors operate, I believe that we would wind up with nothing at all resembling human beings. This being the case, how much less likely it is that organisms evolving over five billion or more years, independently in a quite different environment of another planet of a far-off star, would closely resemble human beings.
    Thus, the hoary science-fiction standby of the sexual love between a human being and an inhabitant of another planet ignores, in the most fundamental sense, the biological realities. John Carter could love Dejah Thoris, but, despite what Edgar Rice Burroughs believed, their love could not be consummated. And if it could, a viable offspring would not be possible. Likewise, the category of contact story, now quite fashionable in some UFO enthusiast circles, of sexual contact between human and saucerian–most recently described in a weekly newspaper headline with the modest title “We Sexed a Blonde from a Flying Saucer!”–must be relegated to the realm of improbable fantasy. Such crossings are about as reasonable as the mating of a man and a petunia.
    A popular phrase–often encountered in popular books on the planets–is “life as we know it.” We read that “life as we know it” is impossible on this planet or that. But what is life as we know it? It depends entirely on who the “ we ” is. A person who is unsophisticated in biology, who lacks a keen appreciation of the multitudinous adaptations and varieties of terrestrial organisms, will have a meager idea of the range of possible biological habitats. There are discussions, even by famous scientists, that give the impression that an environment that is uncomfortable for my grandmother is impossible for life.
    At one time it was thought that oxides of nitrogen had been detected in the atmosphere of Mars. A scientific paper was published on this apparent finding. The authors of the paper argued that life on Mars was, therefore, impossible, because oxides of nitrogen are poisonous gases.