Francis Crick
Francis Crick; drawing by David Levine

Ten years ago, Carl Sagan of Cornell University invited me to go with him to a conference held at a mountain-top astronomical observatory, high above the Armenian city of Yerevan. The conference, sponsored jointly by the US and USSR Academies of Science, had “Communication with Extraterrestrial Intelligence,” or CETI, as its topic. I recall it here since it is directly relevant to the new book by Francis Crick. Certainly it was the most fantastic of the many international scholarly gatherings I have attended. The agenda of the CETI Conference was twofold: to assess the chances that there are any extraterrestrial intelligent (ETI) beings with whom we might communicate (or who might be trying to communicate with us), and to decide on the most practical means by which we (or they) might effect such communication. An interdisciplinary group of about fifty scholars had been invited, mostly from the US and the USSR, to address these two questions.

On the very first day of the meeting it turned out that most of the participants were veteran CETI enthusiasts, who had come to Armenia convinced that there were many ETIs out in space and that radio was the way to get in touch with them. Accordingly, the real purpose of the conference seemed to be the formulation of an effective plea to the US and USSR governments to devote substantial funds to building giant radiotelescopes for CETI—one plan put forward at the meeting, for instance, called for the construction of 1,000 interlinked dish antennas, each 100 meters in diameter, at a cost of $10 billion (1971). The official proceedings of the CETI Conference were eventually published as a book1 and the physicist Freeman Dyson wrote an account of what evidently struck him and many of the others as a memorable event.2

The first part of the conference was devoted to estimating the number, N, of potential ETI conversation partners in our galaxy, by means of the “Drake Formula,” devised by Sagan’s fellow Cornell astronomer Frank Drake. The Drake Formula states that:

N=Rfpf eflfi* fc*ft,

where R is the number of stars in our galaxy, fp the fraction of such stars that have planets, fe the fraction of such planets that are ecologically suitable for life, fl the fraction of ecologically suitable planets on which life actually has arisen, fi the fraction of planets on which, following the origin of life, intelligent beings have arisen, fc the fraction of planets with intelligent beings on which technologically competent civilizations arose capable of communicating with us, and, finally, ft the fraction of such civilizations that still exist at present and still might want to communicate with us.

Since R, the number of stars in our galaxy, is about a hundred billion, the Drake Formula indicates that, as long as none of the f fractions is vanishingly small, there should be many potential ETIs for CETI. Hence, to arrive at an informed estimate of the Drake Formula’s value of N, the conference organizers had brought together a panel of experts that could provide an informed estimate of the magnitude of each of these f fractions. Thus there were on hand some cosmologists and astrophysicists to assess fp and fe, some neurobiologists and psychologists to assess fi, and some social anthropologists and historians to assess fc.3 Though admittedly very rough, the estimate of each of these f fractions turned out to be close enough to the value of 1 that when, according to the Drake Formula, a hundred billion is multiplied by their product, a large number of potential ETIs is predicted.

Sagan had asked me to deal with the last fraction, ft, because I had recently published a little book4 in which I developed the idea that scientific and technological progress is cognitively and emotionally self-limiting. I proposed to the conference that ft, the fraction of ETIs that have arisen and that are still looking for interplanetary conversation partners, is close to zero. I argued that once a civilization has progressed far enough to have radios, the discovery of psychoactive drugs cannot be far behind. So even if there are many ETIs that once listened to radios, by now they are probably all stoned and no longer interested in communicating. None of the CETI enthusiasts took my argument seriously, since it would have cut down the value of N in the Drake Formula to a disappointingly small number.5

I have yet to mention the fraction fl, expressing the chance that life arises on any planet on which physical and chemical conditions compatible with biological processes obtain. To provide expertise for estimating that most problematical of all the fractions of the Drake Formula, Sagan had invited Leslie Orgel and Francis Crick. Orgel was then, and is still today, one of the reading students of the chemical aspects of the origins of life; his book is an excellent general presentation of that subject.6 And Orgel’s long-time friend Francis Crick, who shared the Nobel Prize in 1962 with James Watson for their discovery of the DNA double helix, is regarded by many of his colleagues as the greatest theoretician of biology since Charles Darwin (an opinion that I fully share). Crick’s collaboration with Watson, which in 1953 culminated in working out the molecular architecture of the nucleic acid into which the hereditary information of living beings is inscribed, marked the beginning of the present era of molecular biological studies.


But Crick had not only opened that era; he also dominated it for the next decade or so by formulating the central dogma of molecular biology that has guided studies of living processes ever since. So, inasmuch as the problem of the origin of life is obviously a chemical and molecular-biological problem, Sagan could hardly have made a better choice for expert estimators of fl than Orgel and Crick. Alas, they nearly broke up the conference by insisting, when their turn came to speak, that no estimate at all of fl, however rough or approximate, can be made. Therefore no realistic evaluation of the Drake Formula is possible, particularly not one on the basis of which a case could be made to the US and USSR governments justifying the expenditure of $10 billion for CETI radiotelescopes. After wrangling unsuccessfully with Orgel and Crick for nearly half a day, the CETI enthusiasts finally decided to ignore them and get on with the job of planning for CETI, particularly after Freeman Dyson pronounced that arguments about the magnitude fl were only “philosophy” anyhow, which might as well “go to hell.”

Now, a decade later, Crick has brought out a generally comprehensible summary of the argument about the origin of life that he and Orgel first produced on that Armenian mountain top, facing Mt. Ararat, where Noah’s Ark docked, across the Turkish border. He writes that he has done so even though “every time I write a paper on the origins of life I swear I will never write another one, because there is too much speculation running after too few facts…[but] the subject is so fascinating that I never seem to stick to my resolve.” The central idea presented in Life Itself is what Crick calls “directed panspermia,” namely that terrestrial life may not have originated on Earth at all but, instead, could have been sent here by rocket from another planet by an ETI.7 At first sight, this proposal seems little more than science fiction, hardly worthy of the greatest theoretician of biology since Darwin. But there is more to it than meets the eye, and as I will try to show here, if followed to the bottom of the night it is a truly fiendish idea.

Before taking up the directed panspermia hypothesis, Crick provides a general view of the problem of the origin of life. The universe started with the Big Bang about ten billion years ago and the earliest traces of terrestrial living organisms date to about three billion years ago. So in that interval of about seven billion years, life must have arisen at least once, somewhere. But how?

There seem to be only two ways to go about finding out. We could try to simulate in the laboratory the early conditions of the prelife Earth under which life might have arisen and hope that life will arise again in our test tubes. This method is not too promising, however, since the experiment might take millions, or even billions, of years. Alternatively, we could try to infer from the common biochemical characteristics of present-day organisms the properties of those earliest living forms of which they are all descendants. This second approach is somewhat more promising, since, thanks to the insights brought by molecular biology, we can at least formulate some notions about those common ancestral protoorganisms. They must have contained proteins, composed of specific sequences of amino acid building blocks, which catalyze particular chemical reactions. They must have also contained nucleic acids, in which the specific sequences of the amino acid building blocks that made up the proteins are inscribed according to specific sequences of nucleotide building blocks.

The nucleic acids, moreover, must have been capable of self-replication and of presiding over the specific assembly of the amino acid building blocks into proteins. This process must have been governed by the genetic code which relates the nucleotide sequence to the amino acid sequence, and which—and this is one of the most remarkable facts brought to light by molecular biology—is virtually the same for all extant forms of life.

A number of theories have been put forward to explain just how this system might have started, nearly all of them envisaging that the nucleotide building blocks of nucleic acids and the amino acid building blocks of proteins were formed spontaneously from simple chemicals like methane, ammonia, and water under the conditions of the primitive, prelife Earth. These building blocks were dissolved in the oceans, which, as Orgel has estimated, might then have contained as much spontaneously formed organic matter per cup as chicken soup. One way or another, the building blocks came together and began to catalyze chemical reactions pertaining to their own assembly, first rather crudely and eventually, thanks to gradual refinements of the system through the mechanisms of Darwinian natural selection, more specifically.


Whereas Crick finds some of these theories more plausible than others, he does not believe that any of them has been worked out in sufficient detail and tested to be really convincing. And with this finding Crick reaches a point central for his claim that no estimate can be made of the value of the f1 fraction of the Drake Formula: since we still lack an understanding of the details of the origin of life, it is impossible for us to decide whether it was a very rare event or one almost certain to have occurred. Some scientists have argued that it was almost certain, but Crick tends to the opposite opinion: “An honest man, armed with all the knowledge available to us now, could only state that in some sense, the origin of life appears at the moment to be almost a miracle, so many are the conditions which would have to have been satisfied to get it going.” And if it turns out that the origin of life on Earth was rather unlikely, “then we are compelled to consider whether it might have arisen in other places in the universe where possibly, for one reason or another, conditions were more favorable.”

At the Armenian conference the CETI enthusiasts rejected this opinion of Crick’s by claiming that the origin of life can’t be all that improbable. After all, it did happen once, and so we can be confident that it could happen again. This line of reasoning Crick calls the “Statistical Fallacy,” to the demolition of which he devotes an entire chapter of his book. Let us consider a pack of fifty-two cards, shuffled and dealt at random into four hands of thirteen cards each. What is the chance that a particular set of four hands will be dealt? This chance can be calculated to be extremely small, namely less than one in ten followed by twenty-eight zeros. Every time we deal a pack, we get some particular set of hands, of course, but having got that set does not mean that we will ever get it again in our lifetime. Thus unless the mechanism is known that generated a single event, the probability of its recurrence cannot be estimated. This argument applies with special force to the origin of life, “because if life had not started here…,we would not be here to think about the problem.” The mere fact that we are here necessarily implies that life did get started. For this reason, if no other, we cannot use this fact directly in our calculations.

As for the estimates of the fp and fe fractions of the Drake Formula—the fractions of stars with planets and of planets suitable for life—Crick adopts (and justifies) the view expressed by the cosmologists and astrophysicists at the CETI Conference that there must be many planets in our galaxy, perhaps as many as a million, that are ecologically capable of maintaining life and on which we would find, if not life, at least oceans with a primeval soup suitable for the origin of life. And similarly, he agrees with the estimate of the CETI Conference experts of high values for fi and fc, i.e., of a good chance that once life has arisen, it will evolve into intelligent life with technologically competent civilizations.

Suppose that life did arise on other planets, how long would it have taken to reach the ETI state? Here Crick is of the opinion that, reckoned from the time of formation of the Earth, the evolution of man took an unnecessarily long time, namely about four billion years. He thinks that, given “one or two happy accidents,” this process could have occurred in as short a time span as one billion years. Moreover, many of the million or so ecologically favorable planets were formed much earlier than the Earth, some as early as nine billion years ago. Hence if life did arise on other planets, ETI creatures like ourselves could have been present on some of them already at the time when there was only primeval soup in the Earth’s oceans. That is to say, “there was ample time for life to have evolved not just once but twice over.”

Crick now invites us to imagine that on some distant planet there had evolved an ETI as long as four billion years ago and that these creatures had developed science and technology to a level even higher than that which we have accomplished. They would then have had knowledge of the million or so planets with primeval-soup oceans, including our as yet life-less Earth. Moreover, they (in contrast to my critics at the CETI Conference) would have shared my insight that the lifespan of their technologically competent civilization is self-limiting. Finally, they may have had reason to believe that, for some astrophysical reason, their planet was doomed to extinction. So, to preserve life in the galaxy, they would have set about colonizing another ecologically favorable planet.

But how? Crick argues that, in view of the enormous distance of the nearest such planet and the absolute upper limits to the speed of space travel, it is well-nigh impossible that the ETIs would have tried to send their own kind as colonizers.8 Instead, any such colonization would have had to be made by sending microbes, preferably bacteria. Bacteria can survive in a suspended state of animation the thousands of years needed to reach the nearest habitable planet, and they can be adapted for life under the most diverse conditions. So we arrive at Crick’s explicit statement of the directed panspermia hypothesis: a few billion years ago, a technically advanced ETI civilization sent a rocket (whose features Crick discusses in some detail) carrying a diversity of bacteria or of other microbes, to Earth. On impact, the rocket discharged its cargo into the primeval soup, where, in accord with Genesis 1:22, the tiny creatures were fruitful and multiplied, and filled the waters of the oceans. Thereupon Darwinian evolution took its course, and the rest is history.

Is the directed panspermia hypothesis more than science fiction? Or rather, Crick asks, does it actually matter whether life arose here or elsewhere? Since life must have started somewhere, of what use is it to complicate the issue by transferring the real problem of its origin from Earth to another place? To this Crick answers that “whether life originated here or elsewhere is, at bottom, an historical fact, and we are not entitled, at this stage, to brush it aside as irrelevant.” Moreover, there are even a few facts of life that seem more compatible (admittedly only slightly so) with directed panspermia than with a terrestrial origin of life. One of these is the surprising universality of the genetic code, which I have already mentioned. This would be more easily explicable if it had been brought to Earth in the colonizing bacteria sent by ETI. Another is that the oldest signs of life that we find in the fossil record already have the appearance of full-blown bacteria, without any traces of earlier, more primitive forms. In any case, Crick shows that directed panspermia is a genuine scientific theory, which should not be dismissed out of hand, even though it may, at first sight, seem farfetched.

I now come to the fiendish aspect of directed panspermia, which to my great surprise, Crick does not mention at all in his book but which I found by far the most intriguing part of his argument when he first presented this hypothesis at the CETI Conference. For if it were really the case that terrestrial life is descended from bacteria deliberately sent here a few billion years ago by an ETI, then there is no reason to suppose that the kind of life represented by these bacteria had a natural origin. That is to say, these bacteria, with their proteins, nucleic acids, genetic code, and all, could have been tailor-made from scratch for our own terrestrial primeval soup by ETI molecular biologists with only slightly greater understanding of life processes than our own Orgel and Crick. Those ETI molecular biologists themselves, however, could well have existed in a form of life quite unlike our own, having neither our proteins, nor our nucleic acids, nor our genetic code.

Indeed, it is rather likely that the composition and temperature of the primeval soup from which that distant ETI life first arose would have been significantly different from the conditions on the prelife Earth. It is therefore not unreasonable to suppose that in those ETI creatures biochemical catalysis and self-replication would have been carried out by an entirely different set of molecules. And what that different set of molecules might have been like, of that we cannot have the slightest idea. Hence it appears that, far from being science fiction or a mere hocus-pocus transfer of the real problem of the origin of life from one place to another, the directed panspermia hypothesis raises the specter that the problem of the origin of life may be in principle insoluble. For if the only life that we know did not have a natural origin, and the life that did arise naturally is known to us only via the laboratory artifact it created and of which we are the result, then the roots of Life Itself would be forever lost in galactic space.

This Issue

December 3, 1981