“Directed Panspermia” is the name given to the theory, suggested by Francis Crick and Leslie Orgel, that life did not start spontaneously on Earth but was seeded by microorganisms which reached Earth in a spaceship sent by a higher civilization. Except for the suggestion of purposeful origin, their theory does not differ significantly from the widely accepted view that life originated spontaneously on Earth around four billion years ago when chemical evolution produced basic organic molecules in a primeval “soup.” From these molecules a self-replicating mechanism developed which led to natural selection and the familiar process of biological evolution. Clearly those who believe that life on Earth originated from divine action a few thousand years ago will find no point of contact with this work. Creationists are dismissed as “a nuisance, but so far only a minor one.”
The narrowness of the explicit topic of the book might lead one to question the appropriateness of the rather grandiose title, Life Itself, but in pursuing the Directed Panspermia hypothesis, Crick takes the reader on a variety of fascinating journeys, the “Big Bang,” in which currently accepted theory places the origin of the universe some ten billion or so years ago, to the formation of Earth and its ecology. He leads the reader through a biochemical labyrinth, emphasizing what he calls the uniformity of biochemistry: the uniformity of the chirality, or right- or left-handedness, of organic molecules found in living organisms; the astonishing similarities in the metabolic pathways in widely differing organisms; the use of the same twenty amino acids in all protein synthesis; and the uniformity of the genetic code. All these argue for a common origin for life.
Crick frequently supports his inferences with complex probability estimates, though his conclusions are necessarily tentative. In the course of his wide-ranging study, he provides a lucid account of how, by the process of natural selection, a rare event can become common; a clear description of the functions of the nucleic acids (DNA and RNA) in molecular replication; and some basic considerations relating to the design of spaceships and limitations on their speed. (He concludes that velocities greater than about one-hundredth the velocity of light present insuperable difficulties, so that space travel in which time dilation would be significant is highly unlikely.)
Life Itself ranges from subatomic particles to galaxies, from microseconds to light years. The time scale for molecular vibrations may be of the order of a picosecond (10-12 second); the age of the solar system is about 4½ billion years. The difficulty of comprehending these times and distances is not limited to the lay person. It is inherent in the limitations of the human condition, in which we experience only “ordinary” distances, times, and speeds. It is the same limitation which makes the principles and results of quantum physics and relativity seem to be nonsensical. Scientists may become comfortable thinking on a scale appropriate to their own disciplines: crystallographers are comfortable with Ångstrom units; geologists may be at home with millions of years. They too, however, have difficulty with unfamiliar time and distance scales. Crick wisely devotes a whole chapter to making these enormous and minute times and distances more comprehensible to the reader.
The idea of Directed Panspermia is introduced in the Preface by means of a question asked by physicist Enrico...
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