Intelligent Life in the Universe: The Case for Fence-Sitting, Part One

Gareth J. Medway
Magonia 72, January 2002

There has been some recent debate about the likelihood of intelligent life existing in other solar systems, with specific reference to the UFO question. As you would expect, ETH believers think that intelligent life is probably very common, whilst ETH sceptics suggest that it may be very rare.Both sides are able to support their cases with the opinions of scientists, for the simple reason that scientists are themselves divided on the issue.
For instance, it has often been said that UFOs cannot be spacecraft because interstellar travel is impossible. By contrast, a recent article in Scientific American by Ian Crawford, (1) argues that there are no other intelligent races in the Milky Way, since interstellar travel is so straightforward that any race that arose more than a few million years before us would by now have colonised the whole galaxy. The lack of a consensus among scientists on these issues is further shown by the fact that, though Crawford cites the failure of SETI to detect intelligent radio signals as a proof of the absence of other advanced civilisations out there, his article is immediately followed by one by George W. Swenson which points out the difficulties of using radio to communicate across interstellar distances. This latter effectively disposes of the negative results from SETI as evidence.
Now, to state the obvious, there are two ways of assessing a probability: either one takes a random sample of actual occurrences; or, if one exactly understands the processes involved, one can calculate the likelihood of those processes occurring at any given time. Either method, or both, will establish a probability; but not neither.

We are not currently able to go around sampling star systems and seeing how many of them bear intelligent life. Nor, I contend, do we have any real understanding, let alone exact knowledge, of how it arose on Earth, still less how it may have done anywhere else. So how can we talk about its probability?

To examine this in detail, consider an informal conference which was held in 1961 at the Green Bank observatory, West Virginia, to assess the possibility of communication with other worlds. Frank Drake [right] represented the conference’s central problem thus: N = R* (2)

N is the number of civilisations in the galaxy that are currently capable of communicating with other solar systems. Unfortunately, none of the variables on the other side of the equation are known accurately.

'R*' is the rate at which stars were being formed in the galaxy during the period when the solar system itself was born. Since the age of the galaxy and the number of stars in it are known approximately, the astronomers present were able to say with confidence that a conservative estimate would be one new star a year. This was an example of sampling from observation.

'fp' is the fraction of stars that have planets. In 1961 there was no evidence whatsoever on this point, yet the conferrers concluded that that it “might be as low as one fifth”. Actually, for all anyone knew at that time, our solar system might have been unique. It is only in the past decade that measurement of Doppler wobble has made it possible to detect large Jupiter-like planets around other stars. (Previous reports of the discovery of extra-solar planets eventually turned out to have been caused by observational errors.) Several are now known, making it clear that planets are common, perhaps the rule rather than the exception. (Though it is not proven that rocky Earthlike planets also exist.) But the process of planetary formation is still not sufficiently well understood for us to assign an exact probability to it, in the way that we can say that there is a 50 per cent chance of a tossed coin coming up tails.
'ne' is the number of planets, per solar system, with an environment suitable for life. The only clue we have to this is our own solar system, on which there is only one such planet (though it is thought that Mars may once have had life). One can hardly generalise on this basis, but the Green Bank men did, putting the figure “probably” between one and five.

'fl' is the fraction of suitable planets on which life actually appears, on which they decided that “given a time period measured in billions of years, life must sooner or later appear”, so that they gave it a factor of one. Now, while it has been shown that amino acids might have been formed in the primitive atmosphere of the Earth, it has also been calculated that the chances of them arranging themselves into a strand of DNA is so unlikely that the odds are wildly against it having happened even once in the lifetime of the universe. This has led to various speculations, some saying that this proves that Earth is the only planet with life, though personally I think it most likely there is something seriously flawed in the theory. But without any coherent (still less proven) theory of how life arose here, then we are in no position at all to say how often it is likely to happen anywhere else.

An important lacuna occurred here: they jumped straight from the appearance of life to the appearance of intelligent life. In between these is the appearance of complex, multi-cellular life, a necessary but not sufficient condition for the emergence of intelligence. On Earth, this process is highly mysterious. Up until the late pre-Cambrian, perhaps 650 million years ago, the only life was single-celled. After a short transition period in which there were a few multi-celled life forms, quite suddenly the Cambrian explosion brought into being practically all of the known phyla of life, including many types of sea creature not all that different from their descendants today. This “explosion” took not more than a few million years – only one thousandth of the time that the Earth had been in existence. No one seems to have any idea why so much of the development of life happened in such a short space of time. So, again, in the absence of a plausible theory to explain this, who can say what its likelihood is?

'fi' is the fraction of life-bearing planets on which intelligence emerges. On the basis that two intelligent species, humans and dolphins, are found on Earth, they thought this fraction would be large. But again, can one generalise from the example of our planet alone?

'fc' is the fraction of intelligent societies that develop the ability and desire to communicate with other worlds – again, guesswork.

'L' is the longevity of each technology in the communicative state. The 1961 conference was well aware that nuclear war threatened. So far it hasn’t eventuated, but we are not yet in a position to say that a technological society may last long.

A chain with a link missing is useless, and so is an equation in which even one of the variables is unknown. In the present case, an actual majority of the variables cannot even be estimated. The probability of extraterrestrial life is not therefore currently a scientific question at all. However, there have been recent attempts to settle the argument, one of which has generated a lot of heat, or at least hot air. In the blue corner we have Michael Swords, a professor of natural sciences, who, with the stated motive to defend the ETH as an explanation for the UFO phenomenon, has argued that extraterrestrial life is likely to be very common. In the red corner, Peter Brookesmith, whose unstated motive is evidently to discredit the ETH, and who thinks intelligent life to be as rare as intelligent writing on the subject of ufology.

Swords thinks that the issues are so clear-cut that he gives them just a couple of pages, in naively simple terms like this: “Once life forms on a world in the continuously habitable zone, almost no one believes in anything other than a continued advance in complexity. Though the trick of piecing together advanced eukaryotic cells and multicellular organisms seems, at least on our own planet, to be a tough puzzle (three billion or so years in the solving), once past this barrier the process of forming rich ecologies and ever more fascinating life forms should be unleashed . . . Any world circling a sun-like star with enough time in the habitable zone should develop advanced intelligence, and if the habitat is terrestrial (rather than aquatic), that intelligence should flourish into a materials-manipulating technical civilisation.” (3)

Brookesmith’s rebuttal (4) is, interestingly, about ten times the length of the section of Swords’s essay that he is criticising. He finds Swords’s work to be partial, partisan, tendentious, humourless, fatuous, wrong, erroneous in reasoning, lacking in scientific credibility, and out of date. He also says that it “doesn’t reflect any prevailing scientific consensus”, though it has to be said that on speculative matters like cosmology the “scientific consensus” is as fluid as fashion in popular music. Curiously, Brookesmith does not challenge the assumption that single-celled life may form readily, though as already noted, this is one of the weakest parts of the pro-ETH case, since its occurrence on Earth is totally inexplicable.

Swords makes one definite error when he says: “The way in which planets are arrayed within such [solar] systems is thought to be of a standard pattern: small rocky terrestrials near the star and large solid-cored gas balls farther out.” Evidently this was once “thought” solely because it is the case with our own solar system, but it is not true of most of the other systems recently found, and of course his opponent jumps on this.

In 1994 George Wetherill had proposed that after the formation of the planets Jupiter acted as a “sling shot”, sending most of the comets out into the Oort cloud, whence they only approach the Sun very rarely. If our system had had no Jupiter, he calculated, then comet impacts would be a thousand times more common, a continual bombardment that would have wiped out any complex life. At that time, no Jupiter-sized planet had been detected elsewhere, and a mathematical model of planet formation suggested that gas giants would be very rare; hence, he argued, so would complex life. (5) Less than two years after his theory was published, the first gas giant was found circling another star, to be followed by many others. This is a cautionary example of how hypotheses in this field are routinely disproved by new findings.


Brookesmith nonetheless cites Wetherill’s work as significant, by assuming that inner gas giants (several of which are now known) would not have the same effect as outer ones; he fails to mention that inner gas giants are the easiest planets to detect by the Doppler wobble method, so that other types of planet may be commoner than they currently appear. Moreover, he seems to be advocating a different theory altogether from Wetherill’s, (6) that Jupiter acts as a “guardian” that “attracts incoming objects that might otherwise smash into the Earth”, instancing comet Shoemaker-Levy. Now, obviously, not every comet collides with Jupiter, since there are still plenty of comets around. The most it could do is to catch them one at a time, so that now, after billions of years, there are far fewer than there would otherwise have been. But, since most comets have orbits that take them close to the Sun, an inner gas giant would actually be more effective than an outer one in doing this, since there would be more likelihood of colliding with a planet in a smaller orbit.

Moreover, there are various theories about how comet impacts link to evolution. It is agreed that mass extinctions, such as that which occurred at the end of the Cretaceous era, were caused by the impact of a huge comet or meteorite. Yet, although up to 80 per cent of known species were annihilated by these events, on each occasion a whole new eco-system sprang up almost at once: so that there is no reason to think that such catastrophes may be fatal to life as a whole. Brookesmith himself says: “At the same time, we are here because some cometary impacts have evaded our giant gatekeeper, resetting the evolutionary clock on various occasions and in ways no one could have predicted.” This is a case of having it both ways. Jupiter protects us from comets, which is why we’ve survived; but it doesn’t protect us from every comet, which is why we evolved. One could as well argue on this basis that, were it not for Jupiter, life would have evolved much faster.

Other cosmological theories give a positive role to celestial bombardment. Hoyle and Wickramasinghe have proposed that life originated in space and was brought to earth by comets and meteorites. (7) Recently, Berkely scientists studying the Moon concluded that impacts became far more common on its surface in the past 400 million years. Probably they would also then have become more common on the Earth, from which they suggest that somehow this stimulated evolution, though this would be more plausible if the crash frequency increase had coincided with the Cambrian explosion. (8)

How valuable these theories are may perhaps be judged by the data on Jupiter transmitted by the Galileo probe, which was totally different to what had been expected. Brookesmith comments on this: “If planets in our solar system refuse to conform to theoretical prediction, we can place no faith in smug predictions about the nature of satellites in other systems.” Quite so, but why then, we may ask, does Brookesmith feel confident in making smug predictions about the rarity of intelligent life?

Brookesmith also makes the misleading statement that the Earth is “placed at just the right distance from the Sun to maintain water in its liquid state”. Actually, distance from its star is only one factor determining a planet’s temperature. Venus is much hotter than the Earth, not only because it is closer to the Sun, but due to its clouds creating a strong “greenhouse effect”, and, possibly, its intense volcanic activity. There is in fact quite a wide band in which a planet might have an Earth-like temperature.

Another key point of Brookesmith’s argument concerns the Moon, which on the basis of the currently fashionable “big splash” theory of lunar origins he reckons to be an astronomical rarity. He goes on to say that it has played a key role in evolution, since “It is the Moon’s gravity that tilts the Earth, creating the seasons”. This can hardly be correct, since Mars, which has no large moon, has almost the same axial tilt as the Earth. (in any case, it is merely speculation that the seasons were vital for the evolution of complexity.) Moreover, he thinks, the Moon’s gravity “creates the ebb and flow of tides, so that animals living in coastal waters were subject to yet more evolutionary pressure. Those who could not survive being stranded by the ebb tide died off.” This would not have happened, he avers, but for the Moon.

Now, as every schoolchild knows, both the Sun and Moon exert a tidal pull, the Moon’s being slightly more than twice that of the Sun. Spring tides occur when the two coincide, neap tides when they partly cancel out. So, if there were no Moon, there would still be tides, nearly as great as neap tides, caused by the Sun.

But do tides matter anyway? Passing over the usual tautology of evolution theory (”Those who could not survive . . . died off”) I notice that jellyfish are often stranded by ebb tides and die. Yet whilst the tides kill the individual, as a class they have flourished for at least 600 million years.

The popular equation of evolution with progress has recently been subject to heavy criticism. Zen Faulkes, a contributor to the Prometheus Books study The UFO Invasion, argues that: Evolutionary theory does not predict that there should be any trend to increasing intelligence. For that matter, evolutionary theory does not predict any trend toward any sort of increasing complexity . . . when one considers that the anomalocaridids were Cambrian-era predators with well-developed eyes, raptorial appendages, and reaching two meters in length . . . one is hard-pressed to argue how such an animal would be “simpler” than the vast majority of animals alive today.” (9) In the same way, Brookesmith invokes Stephen Jay Gould for the conclusion that there is in fact “a slight overall tendency toward simplification”.

I don’t know if you can make any sense of that, for I confess that I cannot. If there is no tendency for life to become complex, then how did complexity ever arise in the first place? If there is no tendency towards increased intelligence, then why did intelligence increase? Possibly what they mean is that, under normal circumstances, life should not become complex or intelligent, so that it must have done so on Earth by the veriest chance. If so, then what they are effectively saying is, theory and facts do not agree, so reject the facts as anomalous, and stick to the theory.

Faulkes also writes that “nobody has yet to provide any reliable evidence that those lineages that squeaked through episodes of mass extinction were any more complex or “better adapted” than those that died”. Other biologists echo this, suggesting that Darwin’s hypothesis of natural selection through survival of the fittest has been tacitly abandoned (though no doubt if a Biblical Creationist pointed this out they would deny it). But this leaves us without any theory of the origin of species, so that these people are pontificating on the probability of events that actually they can’t explain at all.

Brookesmith also points to the large amount of randomness that has evidently taken place in the survival and development of species, citing in particular Stephen Budiansky’s The Improbability of the Horse. I suspect that this may be a misleading use of the word “improbability”. Every one of is the result of a genetic lottery at conception, of which there were millions of possible outcomes. So the odds are millions to one against you existing. But, of course, that does not mean that you only came into being as a result of some staggering cosmic coincidence. In the same way, the odds may be incredibly against the exact sequence of life that has occurred, but in itself that does not prove that the probabilities are against something similar having happened.

One thing that is established, from the fossil record, is the general increase in brain size over millions of years, at least in some vertebrates. tertiary mammals tended to have bigger brains than Mesozoic dinosaurs, and modern humans have bigger brains than earlier humans did. We may not know the cause of this, but it is a fact.

The real motive, on both sides, is to avoid those most embarrassing words: “I don’t know”
Here we come up against the problem that, given the incredible complexity of life, the reasons why these complexities evolved must be even more difficult to understand. Evolutionists, however, tend to offer very simplistic explanations. This is what Swords does here: “intelligence is one of the most powerful survival characteristics employable in the struggle for existence.” Consider, again, jellyfish, which have no brain at all, yet have proved adepts at survival. Incidentally, brain size does not directly correlate with intelligence. Certainly, large brains do not seem to have proved much of an asset to people who write about the probability of intelligent life.

Part of the trouble arises from a refusal to admit that biology is not generally an exact science in the way that physics and chemistry are. What we find in the fossil record is a fact, but the reasons suggested why those events occurred are often only guesses. For instance, the “punctuated evolution” hypothesis, that missing links existed for too short a time to leave fossil remains, is by its nature untestable, hence not, strictly, scientific.

However, I think that the deepest issue here is not about science at all. Brookesmith accuses Swords of having “a core of religious faith”, implying that this is something to be despised. Whatever the official position may now be on natural selection, biologists still hold fast to Darwinism because it “has no place for a divine guiding hand. But Swords’s complaint should apply equally to particle physics, organic chemistry, geology, astronomy, or any other scientific discipline deserving the name, as no science reserves such a driving seat for the Almighty.”

Actually, the physical sciences are rooted in the notion of a structured universe that obeys precise laws – even unpredictability, in quantum physics, follows exact rules. Science does indeed have no place in it for the divine, because science deals with “efficient” (immediate) causes, not with “final” causes, into which category the question of whether or not the universe has a purpose falls. Science is impotent in the face of the ultimate issues.

Because of this, it may be noted, some possibilities are never discussed. If Einstein was right when he said “God does not play dice”, then events that we think are random actually have a cause currently unknown to us. Einstein was talking about microscopic interactions, but far all we know the remark might apply to the cosmos as a whole.

The “intelligence is common” school often invoke the “Principle of Mediocrity”, that we do not occupy any particularly special position in the universe. This is a philosophical guideline, often useful in astronomy, but not an unbreakable rule. If planets with intelligent life are very rare, we would have to be on one of those privileged places to be able to debate the question at all.

On the other side is what one might term the “Egotistical Principle”, that humans have one of the most honoured places in the scheme of things. In the old days, when the Earth was thought to be the centre of a universe perhaps only a few thousand miles across, and before random forces had been set up in the place of deity, it was accepted that everything was created for the benefit of man, who was made in the image of God, woman being a second-rate imitation. No one suggested, though the position would have been equally sustainable, that the world existed for the sake of, say, locusts, and that the function of humans was merely to cultivate crops, so that the locusts could eat them.

Nowadays things are contrariwise: the universe is vast, and presumed to be random. To keep up our special position it has to be assumed that the planet Earth is one of the few places, preferably the only place, where intelligent life has happened to arise. Of course, this motive is never admitted aloud.

If we prove to be alone in this vast universe, then we will be more ready to admit ourselves to be a mere product of chance. Conversely, if life on other planets is very common or even, as abduction literature suggests, so similar to that on Earth that ETs can interbreed with us or create hybrids – we may well conclude that the universe is not an accident after all. So the existence or otherwise of extraterrestrial life may be the ultimate litmus of the materialist and religious viewpoints. This may explain why so many people are trying to jump the gun and answer the question before they have the evidence.

That said, everyone in this debate is suffering from the same basic flaw in approach, that they present unproven speculations as if they were proven facts. The real motive, on both sides, is to avoid those most embarrassing words: “I don’t know”.


  1. “Where Are They?”, Scientific American, July 2000
  2. Walter Sullivan, We Are Not Alone, Pelican, 1970, p. 280
  3. Michael D. Swords, “Extraterrestrial Hypothesis and Science”, in Jerome Clark, The UFO Book, Visible Ink, Detroit, Michigan, 1998, p. 191
  4. Fortean Times, 134, 135, 136, May-July 2000
  5. Astrophysics and Space Science, 212, 1994; also Nature, 373, 1995
  6. Though he nevertheless cites Wetherill as his authority. He also quotes Geoffrey Marcy of California State University, but does not state Marcy’s (unproven) theory, that inner gas giants must have started as outer gas giants in decaying orbits, and would have eaten up earthlike planets on their path towards the Sun. See Washington Post, 15 February 1999, A3
  7. Fred Hoyle & N.C. Wickramasinghe, Lifecloud, Sphere, 1979
  8. Science, 10 March 2000
  9. Kendrick Frazier, Barry Karr and Joe Nickell, The UFO Invasion, Prometheus Books, Buffalo, New York, 1997, pp. 306, 308.