Life Itself

Life Itself (1981) is a work of popular science by Francis Crick, the “doyen of modern molecular biology” (New York Times) whose groundbreaking work led to the discovery of the molecular structure of DNA. Life Itself addresses this topic, but only indirectly, in the course of advancing a hypothesis which Crick himself admits is tenuous: that life on Earth may have been deliberately “seeded” by an alien civilization. Crick argues that even highly speculative inquiries into the topic of the origin of life are worthwhile: “Once the scale and nature of the galaxy is appreciated, it is intolerable not to know whether we are its sole inhabitants. It may even be very dangerous not to do so….To show no interest in these topics is to be truly uneducated.”

Crick dubs his hypothesis “Directed Panspermia.” The original “Panspermia” hypothesis, devised in the 19th century, attempted to solve the problem of the origin of life by suggesting that life—along with matter—is eternal, and therefore has no origins. However, since the planet Earth, at least, is provably not eternal, but only a few billion years old, the hypothesis faced a problem: how did life arrive on Earth? Crick’s hypothesis provides an answer: alien civilizations sent microbes into space in order to colonize new worlds.

In search of evidence for his hypothesis, Crick turns to his area of expertise: molecular biology and the genetic code. He points out that every living being on Earth depends upon the same genetic code, that in this sense, life on Earth is completely unified: “I find it a curious symptom of our times that those who derive deep satisfaction from brooding on their unity with nature are often quite ignorant of the very unity they are attempting to contemplate. Perhaps in California there already exists a church in which the genetic code is read out every Sunday morning.”



For Crick, this raises a question: if life emerged on Earth, why are there not many different genetic codes in operation? If it were possible for life to emerge spontaneously on Earth, it might be expected that several different kinds of life—each coded differently—would have emerged at different times. The same result might be expected if the complex forms of life we know today all had their origin in one simpler genetic code: natural selection would have produced a diversity of variations on this original code. Even if only one code arose, at the very least, Crick argues, natural selection should have caused different organisms to adopt different codons for different amino acids. In fact, every organism on Earth uses the same code and the same codons.

Crick explains this by an analogy to language. Different human languages—say, Spanish and Mandarin—use different alphabets, and even among languages that use the same alphabet—say, Spanish and Finnish—the symbols of the alphabet are combined according to different rules. However, the “language” of life has one alphabet, always combined according to the same rules.

Crick suggests that one way to determine whether life on Earth originated on Earth would be to find an element commonly used in the structure of life which is not abundant on this planet. He admits that no such finding has been made, however, he does suggest that the role of molybdenum in organic chemistry is surprising. Although it is present in seawater, it is comparatively rare on Earth, but essential to the processes of life. If life originated on Earth, one might expect life-forms that evolved to rely on other, more common elements to have a clear advantage and so displace molybdenum-using life-forms. Crick argues that this may suggest that life on Earth originated on a planet where molybdenum is more common than it is here. However, Crick concedes that the abundance of molybdenum in the oceans makes this an inconclusive argument at best.



Lastly, Crick argues that the period between Earth becoming suitable to harbor life and the appearance of the first fossils is shorter than might be expected: indeed, it might one day be possible to show that life did not have time to emerge naturally.

Crick turns to his alternative explanation. First, he sets out the age and size of the Universe, as currently known to science, arguing that, given the time and distances involved, it is possible—even likely—that other intelligent civilizations exist somewhere: “People are happy to contemplate the limitless powers of God—a doubtful proposition at best—but quite unwilling to meditate creatively on the size of this extraordinary universe in which, through no virtue of their own, they find themselves. Naively one might have thought that both poets and priests would be so utterly astonished by these scientific revelations that they would be working with a white-hot fury to try to embody them in the foundation of our culture.”

Such a civilization could have built spaceships to seed the universe with life. Indeed, our own history suggests that such a course might become imperative for an advanced civilization. Crick points out that it is easily possible to imagine a near future in which humans realize that life on Earth is likely to end. In that scenario, we, too, might send microbes into space, in order that the experiment of life not end with us.