Evolving the Alien: The Science of Extraterrestrial Life 
by Jack Cohen and Ian Stewart.
Ebury, 369 pp., £17.99, September 2002, 0 09 187927 2
Show More
XTL: Extraterrestrial Life and How to Find It 
by Simon Goodwin and John Gribbin.
Weidenfeld, 191 pp., £12.99, August 2002, 1 84188 193 7
Show More
Show More

In the middle of the 19th century the prevailing scientific view of the abyssal ocean held that it was a vast body of water with a uniform temperature of 4 °C. With no variation of temperature there could be no convection currents, hence no circulation of dissolved oxygen and suspended food particles. The abyss was stagnant, a body of water under massive pressure, barely warmer than freezing and utterly without light. Thus, reasoned the scientists (influenced, no doubt, by human physiology and the Book of Genesis), it could not conceivably support life. The Manx naturalist Edward Forbes coined the word ‘azoic’ to describe this self-evidently lifeless zone. By the 1870s he and other oceanographers were eating their words as improved sampling technology retrieved abundant evidence that, in cheerful defiance of human preconceptions, even the deepest abyss was teeming with life.

A cautionary tale, one might think, for scientists of the early 21st century engaged in planning space missions to find extraterrestrial life. Expressly shunning an anthropic approach, the authors of Evolving the Alien insist that the fledgling science devoted to discovering extraterrestrial life-forms should be known not as ‘astrobiology’ but as ‘xenoscience’. They are combative on this point, and so united that they frequently refer to themselves as ‘Jack&Ian’. To this winsome dyad the notion of astrobiology is limiting in that it stands for astronomy as seen from Earth plus Earth-style biology, so that its thinking is governed by anthropic concerns such as the search for ‘habitable zones’ elsewhere in our solar system, just as we once looked in the oceans. Jack&Ian is feistily scornful of ‘habitable zone’ thinking, partly because he knows how life constantly confounds human expectations of what is habitable and partly because he has in mind life-forms quite unlike terran creatures, with properly alien chemistries and biologies to match.

Most formative thinking about the genuinely alien has been done by science fiction writers, and Cohen and Stewart provide their own short SF story about how an unknown creature might perceive a Nasa probe sent in the near future to Europa, a satellite of Jupiter. (There are great hopes that life might be found in the ocean that is believed to lie beneath its frozen surface.) They also dot their text with plot summaries of thirty SF classics in order to illustrate their scientific points. Part of their task is to debunk popular misconceptions about what alien life-forms might be like. They are merciless with anthropomorphic nursery and cinematic imagery (ET and Star Trek), the fallacies underlying the cod science of Jurassic Park and the loony gospel of UFOs and alien abductions.

Since they start from a strictly Darwinian account of terrestrial evolution they can assert that however alien life-forms may turn out to look, there is virtually no possibility that they will resemble Homo sapiens. We can forget humanoids such as Mr Spock and the Klingons because Homo evolved under a uniquely changing series of terran conditions. What is more, even if evolution could be rerun, contingency would guarantee that next time around it would not follow the same path. Stephen Jay Gould’s book Wonderful Life, about the fantastic evolutionary dead-ends fossilised in Canada’s Burgess Shale, makes this point beautifully. We and other land vertebrates owe our eyes-above-nose-above-mouth features and our awkwardly intersecting windpipe-and-gullet arrangement to a lobe-finned fish that happened to make it ashore. (The bad design of this airway-cum-throat means that people occasionally choke to death, but too infrequently for the feature to have been deselected by evolution. A similar awkwardness can be seen in the bizarre mix-up of our genital and excretory organs.)

It is crucial, so far as Cohen and Stewart are concerned, that there is no satisfactory and generally agreed definition of what life is – and therefore no way of being certain we would recognise it in alien guise. They don’t quote Nasa’s current tentative definition (‘a self-sustained chemical system capable of undergoing Darwinian evolution’), probably because they find it possible to imagine conditions in which life-forms might not replicate according to natural selection. But they do quote Stuart Kauffman’s definition, according to which a life-form is any ‘autonomous agent’ that can reproduce and carry out at least one thermodynamic work cycle. In other words, it would have to be able to redirect energy so as to ‘pump up’ processes back to their starting point, and to pass that ability on to copies of itself. Life could even be a vacuum, which at a quantum level has more than enough complexity to organise itself into an autonomous agent. If a living vacuum seems an imaginative step too far, it is worth considering what we understand as being ‘alive’. The bacteriophage known as T4 is a parasite of the bacterium E. coli that thrives in the human gut. It looks like a spacecraft with a geometrical cabin perched on a vertical column, at the bottom of which are six folding legs. The phage has no organising brain whatever, not even a nucleus. It is an entirely chemical robot that lands on the surface of E. coli, dissolves a hole in its host with enzymes and injects a rope of DNA. The rope contains more than 150 genes that immediately shut down most of the bacterium’s functions, leaving active only those that can set about replicating copies of T4 and its DNA. This entire, submicroscopic whirl of precise activity involves nothing but blind chemical reactions. Is T4 alive in any meaningful sense? The question will remain unanswered until science has devised a theoretical, molecular-level explanation that can say precisely when ‘dead’ chemicals constitute a ‘live’ organism. Theology is hardly an issue, but philosophy might enjoy adding its tithe.

Meanwhile, Cohen and Stewart describe how inanimate clays can ‘organise’ themselves and self-replicate (much as crystals grow in saturated solutions). In the presence of the right catalyst, simple chemicals can become complex and in turn autocatalytic: one of the most persuasive of current explanations of how life began on Earth. Such phenomena seem to tally with computer simulations and experiments which have shown repeatedly that systems have the ability to evolve themselves out of apparent chaos. This effectively debunks the assertion that ‘life is too complex to have arisen spontaneously,’ and it now seems to be established as a general principle that in the right conditions simple chemistry becomes complex and can eventually organise itself: become, effectively, alive. The ‘live’ polio virus, for example, has recently been created from scratch using its genetic sequence alone, although the process was extremely slow and tedious.

The value of Cohen and Stewart’s speculative, imaginative, even fanciful approach is that it enables them to cover a lot of very useful ground. At its best, it exposes flaws in popular thinking and is painlessly educative about the present state of science in matters including the pervasive misreading of evolution as ‘succession’ or ‘progress’; Gaia; the possibility of building Arthur C. Clarke’s space elevator; the alternatives to DNA/RNA-based life. They also examine the probable flaw in SETI, the Search for Extra-Terrestrial Intelligence – this has been listening out for radio messages for decades and is now a worldwide co-operative effort using the downtime of thousands of personal computers. Cohen and Stewart point out that our present radio and TV transmissions employ coding that would have been quite unintelligible to us only fifty years ago: we wouldn’t even have been able to distinguish a modern digital signal from background white noise. SETI is maintained, nevertheless, in the hope that we will receive transmissions we can recognise as such.

The account of SETI in XTL (a zippy acronym for Extra-Terrestrial Life) is more technically detailed, and lacks Jack&Ian’s scepticism. But then, XTL is a very different book. For a start, most of it is exclusively about astronomy. It belongs, in fact, in the category of Jack&Ian’s despised astrobiology. Unlike Jack&Ian, Simon Goodwin and John Gribbin are very keen on habitable zones, drawing two concentric spheres of habitability out from the Sun to mark the limits between which it might be worth looking for life. After reading Evolving the Alien this feels conservative, as well it might when one sees Goodwin and Gribbin’s diagram showing the life zone here on Earth stretching just 25 km from below the seabed to the stratosphere. I don’t understand this. In the last decade live bacteria have been found at a height of 41 km, where they evidently deal very adequately with scorching ultraviolet radiation that would swiftly do for us, and Archaeans (ancient bacteria-like organisms) have been found alive and well in rocks 3 km underground. This nearly doubles Goodwin and Gribbin’s zone of habitability, and further research will probably reveal it to be even larger.

This impression of being slightly out of date may betray lingering ‘azoic’ tendencies, possibly because Goodwin and Gribbin are astronomers. But then they go on to examine which planets in any system might fall into the habitable zone, ruling out those whose orbits are close enough to a star to become tidally locked, so that they always present the same face to the star ‘just like the Moon relative to the Earth or Mercury relative to the Sun’. What was that again? Mercury rotates once every 58.65 Earth days, a fact that was revealed by Doppler radar observation in 1965 and made ruthlessly public – it’s even in Patrick Moore’s 1967 edition of The Observer’s Book of Astronomy. XTL was published as a hardback in 2001. Did nobody notice? It’s not a typo and Goodwin and Gribbin both have a PhD in astronomy. Whatever the reason, the error inevitably casts something of a penumbra over the rest of the book. The last chapter, ‘Searching for Civilisation’, does deal with several of the topics that Jack&Ian covers (such as SETI and the Drake Equation for estimating the number of civilisations Out There), but not in such discursive detail. The pictures are nice, however.

The one thing these books share is a naive optimism. Both end with confident speculations about technological breakthroughs that will soon make space travel easy. It is theoretically possible even now, although primitive and hopelessly time-consuming; but soon? Theirs is a grand vision of the kind unmoved by the spectacle of space shuttles breaking up on re-entry. This is how Jack&Ian ends Evolving the Alien: ‘Will we find alien life? Or is there a supervening reason for us to be the only ones, ever, in the Great Adventure? Surely not. In less than two hundred years, we will know.’ Why two hundred years? This is an authorial guesstimate based on Jack&Ian’s conviction that ‘we’ (though not I) will have discovered some sort of warp drive by then that will set us Trekking around the nearer stars. Here Jack&Ian’s scepticism stops while mine goes galloping on.

For whatever reasons – age, the present threatening political and environmental situations, or my having lately read John Gray’s highly unsanguine Straw Dogs* – I cannot see why the discovery of extraterrestrial life would any longer be such a prodigious deal. Fascinating, certainly, but not miraculous; and certainly not (in Goodwin and Gribbin’s words) ‘arguably . . . the most profound discovery in the entire history of human civilisation’. What, more than that of mayonnaise? Many of us have long had no difficulty in assuming the likelihood of life existing elsewhere in the universe. I take their hyperbole to spring from an unconscious cultural inheritance rooted in the biblically implied uniqueness of the human race. In this same mood I can see that although SETI is mediated by glittering technology, it is essentially a religious activity. The plaintive human cry ‘Is anybody out there? Please?’ has echoed down the millennia and now, borne on inscribed tablets and radio waves, is heading out of our solar system. Like any religion, SETI’s hope of receiving an answer requires belief and occupies thousands of waking hours, often whole lives. And why not? Jack&Ian provides some pretty good reasons why SETI is unlikely to turn up aliens, but who knows?

No matter how corrective Jack&Ian’s science may be, it is hard not to feel that a lot of this essentially optimistic speculation is grandly inconsequential, even blatantly escapist. It is easy to decry the way in which popular ideas of the alien are constructed from nursery imagery and infantile fears, but when Jack&Ian breathlessly invokes a phrase like ‘Grand Adventure’ to signify humanity’s blasting off into the unknown he is obviously deaf to its echo of Peter Pan’s mawkish assertion that ‘to die will be an awfully big adventure.’ It is also fine to throw out phrases like ‘we will soon be able to cross the gaps between stars’; but who is this ‘we’, and why the implied immediacy, even urgency, of all this?

This is a category of rhetoric common to much popular science, often self-parodied by the New Scientist in its shock-horror headlines (‘Crunch time soon?’) referring to claims that the universe will collapse within the next ten to twenty billion years. ‘Soon’ is good, and so are the equally excitable stories about the danger of our imminently falling victim to rogue asteroids, black holes, wormholes in space-time and the rest. We have reached a point where researches into the geological and palaeontological past, as well as the astronomical future, are yielding great quantities of data, much of it speculative but some of it very detailed. The data are so readily retrieved and downloaded, their popular presentation so vivid and present-tense, it is as though they referred to last Tuesday or next Thursday. Past and future have both been telescoped. Millions of schoolchildren are so familiar with T. rex that the animal is in some sense alive still. Millions, too, regularly encounter speculation about the newest theories of cosmology and xenoscience – to say nothing of SF tales and virtual reality games – and probably feel interstellar or multi-dimensional travel are already pretty much fact, if only they knew where to buy a ticket.

This is fine for our imaginative self. But for our fleeting physical self locked in its photo-flash of a lifetime it is irrelevant. There is no living T. rex; there is no star travel. Instead, the human race’s very survival for even the next two hundred years may well depend on its reluctantly dragging itself away from exotic futures and addressing the disagreeable realities of the now. Contrary to Jack&Ian’s belief, technology is not an entirely autocatalytic system. Scientific knowledge itself might be unstoppable; but converting knowledge into costly hardware usually intersects with dicey politics. And that’s without taking into account the social and political consequences of currently metastasising technologies (especially genetic and pharmacological ones) which, like it or not, have already begun the process of re-engineering the human animal, something that might be thought of more immediate concern to us than the putative physiology of alien species. In such a confrontation SF begins to look like a weapon of mass distraction. Besides, only governments can hope to fund fabulously expensive Big Science projects such as exploring the planets and their satellites. At this moment the one nation whose technical achievements have inspired so much cosmological and SF dreaming looks like becoming bogged down for the foreseeable future in managing its recalcitrant earthly empire; nor can it ignore the human and PR costs of the inevitable disasters that attend space exploration.

In any case there is surely a fallacy underlying Jack&Ian’s castigation of anthropocentric attitudes. On the off-chance that humans do eventually encounter aliens (the most we can realistically hope for in our own solar system is bacteria or primitive aquatic organisms), those explorers will inevitably be trying to grasp them with human minds. They can purge themselves of all the cultural baggage they like, but their intelligences will be irreducibly that of Homo sapiens. The authors therefore seem merely to be saying that our descendants will need to be maximally broadminded, both scientifically and ethnologically. But that is no more than Star Trek was saying thirty years ago, with a cast of middle-class Californians doing their best to be enlightened – exactly the terms on which Jack&Ian is dismissive about the series.

What of an alien viewpoint of our strange race? Both these books mention the Fermi Paradox: why, if the galaxy is full of advanced civilisations, are they not already here? I would refer them to the words of Calvin in Bill Watterson’s immortal strip cartoon, Calvin and Hobbes: ‘Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us.’

Send Letters To:

The Editor
London Review of Books,
28 Little Russell Street
London, WC1A 2HN


Please include name, address, and a telephone number.


Vol. 25 No. 7 · 3 April 2003

James Hamilton-Paterson's literary approach to the search for extra-terrestrial life (LRB, 6 March) – typified by the use of a trivial quotation from Calvin and Hobbes in dealing with the complex Fermi Paradox (if they exist, why haven't they contacted us?) – provides little information on the actual progress now being made. The search for signs of life on Mars, on the Jupiter moon Europa, and on other planets orbiting nearby stars is well underway, in both Europe and America, and is coupled with a deepening understanding of the origin of life on Earth. In addition, thanks to the privately funded Allen Telescope Array and the prospective Square Kilometre Array, we are near to being able to detect radio emissions similar to our own from enough targets to have a chance of finding a civilisation passing through the (presumably short) phase of radio-emitting technology.

Alan Penny
Rutherford Appleton Laboratory, Didcot, Oxfordshire

Vol. 25 No. 9 · 8 May 2003

Alan Penny (Letters, 3 April) says that James Hamilton-Paterson’s quotation from Calvin and Hobbes – ‘sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us’ – is a ‘trivial’ way of ‘dealing with the complex Fermi Paradox (if they exist, why haven’t they contacted us?)’. Presumably, since the words are no more trivial than Penny’s own, he thinks they’re trivial because they appear in a comic. Art Spiegelman’s far from trivial work on the pages following Hamilton-Paterson’s review should have put paid to that idea. Penny goes on to enthuse about the technological advances which mean we’ll soon be able to pick up radio waves ‘from enough targets to have a chance of finding a civilisation passing through the (presumably short) phase of radio-emitting technology’. A pretty slim chance, surely? And even if we picked them up, how would we be able to recognise them? Besides which, any intelligent alien life-form sufficiently like us for us to recognise it would presumably be able to recognise us, too. And anything smart enough to intercept and understand our satellite TV news would also no doubt be smart enough to keep well clear. Which takes us back to Calvin and Hobbes.

Jonathan Bland

send letters to

The Editor
London Review of Books
28 Little Russell Street
London, WC1A 2HN


Please include name, address and a telephone number

Read anywhere with the London Review of Books app, available now from the App Store for Apple devices, Google Play for Android devices and Amazon for your Kindle Fire.

Sign up to our newsletter

For highlights from the latest issue, our archive and the blog, as well as news, events and exclusive promotions.

Newsletter Preferences