A second question that the discovery of extraterrestrial life raises, is the matter of evolution and the origin of life. Sagan and his colleagues believe that if life is discovered on other planets, evolution can no longer be denied by creationists. Their assumption is that given the right conditions, life just happens, and has indeed begun spontaneously all over the universe. This seems contrary to all available evidence. From a scientific point of view, the origin of life on this planet is still a mystery.
Most scientists believe life originated by chance.
Those searching for life on other planets believe its coming into being is simply a matter of having the right conditions. It's like a law written into the universe. Many books, some serious, postulate that visitations from outer space have already occurred, and primitive earthlings called them gods, thus explaining the origin of religion. Frank Tipler, a physicist, believes intelligent life must be distinctive of earth, because if there are civilizations out there, most certainly some of them would be far more advanced than our own. Since we have not heard from them we must be alone.