Essay on Panspermia
(Version ii or thereabouts)
Further correspondents and events *
Sitting down onto brass tacks. *
A few definitions and implications *
A few views with room *
A Little bit More and a very little bit Less Doubt *
Well What about the Interstellar Sea of Life, then? *
Problem of scale in Earth as it is in Heaven. *
Macadamias, Monkeys and Combinatorics *
Heuristics in Space *
Sex and Sterility in a Closed Universe *
Our Universe is Small, Small, Small *
You Can't get Here From There *
... and Two smoking Barrels *
Old Bottles with Unsuspected New Wine *
Kinky Sex Won't Cut It *
Recent remarks from the front lines. *
Proof by Assertion *
Occam in a Subterranean Spin *
Betting on probability *
Fastening seat belts *
Rising from brass tacks *
Appendix: Critical Conditions for Progressive Enlightenment *
Historical background to this essay
Some time ago I wrote the original version of this essay in something of a hurry and without any serious background research. My grounds for confidence at that time were the general knowledge appropriate to a biologist, plus miscellaneous reading and intermittent argument during the past few decades. Since the first draft got published in CCNet, it has been subjected to a job lot of largely good-humoured criticism, for which I am grateful. In particular I have debated several issues with Brig Klyce, whose site at the time of writing is accessible at http://www.panspermia.com
Since this is not intended as a polemic, I nowhere cite Brig nor anyone else directly in this version of the discussion, preferring (as I am sure he also would prefer) that interested readers get his views directly from source, rather than filtered through my prejudices. For one thing, that way I am not lumbered with the responsibility of keeping readers up to date with his views. His correspondence has influenced some of the revisions to the original form of this essay, but in my editing I have not distinguished items inspired by his criticism, from any other material and no particular proposition should be attributed to him without first checking it against his web site.
Suffice to say that Brig and I have disagreed almost comprehensively, not only on matters of fact, but on more importantly on matters of theory and even more strongly on matters of emphasis.
In my experience this is usual in dealing with committed panspermists. Perhaps it reflects an intellectual deficiency that I have yet to outgrow. (False modesty? Never heard of it!)
Anyway, there have been so many developments lately that I cannot cover them all in depth without writing a book. This is not what I am trying to do, so please excuse me if my coverage of the field is frustratingly cursory.
One item that has shocked me in discussions since the original version of this essay, was what I, in my arrogance, regard as gross misconceptions concerning the nature and process of evolution and its relevance to Panspermia (or vice versa!) Nothing like a balanced discussion of evolutionary implications could fit into this one essay, so I refer interested parties to, for preference: the web site http://www.talkorigins.org and the book "Darwin's Dangerous Idea" by Daniel Dennett. They are in themselves far from adequate and there are at least dozens of other excellent sources, but these two strike me as exceptionally good starting points for the scientifically literate non-evolutionist confronted with polemical discussion of Darwinian pros and cons. For one thing, they are particularly rich in references to other sources.
There is also of course, scope for a great deal of homework on, for example, cosmology, celestial mechanics, biochemistry, current research, and science itself. I cast no stones, but some of the hottest contributions come from some who could profit most dramatically from some serious and strenuous preparation.
No names, no pack drill.
Further correspondents and events
Since Brig and I argued about it and about, a good deal has happened and apart from what I have encountered in my general reading, I have been emailed with some not necessarily unfriendly, but certainly passionate communications concerning recent studies of meteoritic material and so on. I did not see much of what I received as invalidating anything I said before, but it is good sense to be aware of current concerns and anyway, to ignore good-faith correspondence sits uneasily with me, so I am dealing with some of the material in this updated version. The author of the main communication I received has not called again, so I am unable to assume that he is willing to be identified in the debate. I therefore shall neither name him, nor extensively quote him directly. Should he read this version of the essay, he is welcome to take issue.
Recently there also have been several exultant press reports, mainly nth-hand. I am not making any attempt to cover them comprehensively, nor even systematically. Would eclectically do? Well, at least arbitrarily!. Readers interested in the field will recognise much of the material anyway and are welcome to belabour me for misrepresenting or labouring sensitive points.
Sitting down onto brass tacks.
Panspermia as a concept is not intrinsically implausible, but in science it has played a minor, inglorious role to date and its inglory is not on the wane; not to my eye anyway. It broad rejection need not specifically stem from conspiracy among a scientific establishment which is blinder, more hidebound or malicious than it need be; in fact at the time of revision of this essay, several recent developments are being warmly discussed, such as the significance of high altitude recovery of bacteria and the detection of putative microbial fossils in lunar and Martian fragments. Even if theories of establishment conspiracy were justified, that would not change the fact that any hypothesis must meet certain standards if it is to be taken seriously. It must meet even more if it is to be accepted as a leader among viable alternatives. In everyday life this is largely true, and in science it ideally should be strictly true.
A few definitions and implications
For a start, one serious difficulty is that Panspermia as a concept is very poorly defined. In any sizeable group debating the subject, it is a good bet that not everyone is discussing the same thing and it is an unusual participant who consistently discusses the same concept. Granting that it is a small intellect that has room for only one idea at a time, debate can settle points far less painfully and expensively if one maintains competent control of context, both in discussion and one's own mind.
Arguments nominally in support of Panspermia range from academic musings about specific points, to passionate and partisan advocacy of comprehensive doctrines. At one extreme are tenuous speculations that SOME viable living material COULD at SOME TIME have been splashed off a planet or have got cobbled together in space and SOMEHOW survived indefinite periods of exposure to radiation and free radicals and IN PRINCIPLE have arrived intact on a receptor planet AND established a viable population.
To a biologist, this is not strictly impossible, but that does not imply that it is therefore plausible enough to be interesting. After all, in terms of strict logic it also is hard to refute the Tooth Fairy Hypothesis. At least the Tooth Fairy has the advantage that we can check under our pillows for the transmutation of discarded hard tissue into welcome hard currency. How are we to distinguish a living world, which is as it is because a single molecule fell to Earth 4e9BP, from a similar living world whose life originated 4e9BP in local clays? And if that distinction solves the problem of how life originated on this planet, how does it solve the problem on that planet or cosmic cloud on which life originally originated?
The difficulty of proving negatives is the kernel of the justification of falsification as the basis of modern scientific practice. The combination of unfalsifiability with limited practical consequences, does not make for a rewarding field of research.
At the other end of the scale, zealots tout, more or less as received wisdom, the continuous and effective universal dissemination of viable spores or viruses from planet to planet throughout the universe. One correspondent has spoken to me about osmotic infestation, by which I take it, he means something like a constrained drunkards walk. To my mind this would imply that we must accept not only a steady state universe, but something like steady state life as well and in fact some prominent voices seem to advocate just that.
So let me propose a bit of ad hoc terminology to simplify discussion of alternative options. One of my correspondents suggested that we call the theory of the local origin of life on Earth Endogenesis and the theory that life originated elsewhere, whether in space, on rocks, comets or alien planets, Exogenesis. I don't like the terms and would prefer something more etymologically specific, but I accept that some such terms would be useful. I invite opinions on the most desirable terms, but suggest that in context simply "indigenous" and "exotic" would do as well as any. We do not need specific jargon for that concept.
For the idea that we here on Earth, near-miraculously picked up just a single or at most a few exotic "spores" that ignited our biosphere, let us coin the term "oligospermia". I shall discuss why I do not regard oligospermia as being either of much practical importance if true, or as being persuasive at all as a theory (but pay your dues and make your own choice!) Oligospermia would be consistent with there having been just one or a very few such events, not necessarily all viable. How to prove that nothing of the kind ever occurred, I cannot imagine, but until Occam's razor lets me down, I favour the simpler hypothesis.
In contrast consider polyspermia. That would be the idea that interplanetary infection is rare, but not vanishingly rare. Any planet with a good fertile ocean full of abiogenetically generated organic matter could expect enough visitors to get a viable biosphere going in a few hundred million years. This would imply a far richer supply of sperm sources than oligospermia does, and therefore it would, if the idea proved be viable, suggest a far more plausible source of the original planetary inoculation.
Finally let's consider Panspermia proper, which I propose as referring to the next step up: that the universe is more or less awash with cosmic sperms and practically every planet is continually, or at least frequently (say more than once per century) peppered with viable organisms that survive on the planet. In the extreme form, this process is seen as driving evolution on the planet ans as the source of new strains of epidemics.
We shall discuss some implications of these alternatives as we encounter them.
The foregoing is pretty close to what I have written in the past, but one recent development is the introduction of the terms "bioastronomy" and "astrobiology". I regard them as very useful because they may serve as a basis for separating the polemicists from the scientists. Personally I prefer the latter and shall use it in this essay. As I interpret it, astrobiology would be the discipline concerned with life outside this planet, its origin, nature, and of course, dissemination and genealogy. Scientifically this is completely unexceptionable, even if it turns out that for practical purposes Earth life is unique in the universe. Panspermia as a term in any case bears the implication of the effectively universal presence of life, whereas astrobiology as a term implies no such thing. The neutrality of the term "astrobiology" does not demand that life occurs everywhere, in most places, in a few places, or even just in our stellar back yard.
As a personal opinion, I suspect that astrobiology will rapidly develop two poorly-differentiated branches: one dealing with biochemistry, molecular biology, information theory and palaeontology, and the other to rival cosmology in its reliance on unique, often marginal observations and speculative theories derived from them. I do not denigrate the field for this; in science any work that enables us to bring more material to bear in discriminating in favour of one hypothesis in preference to another earns respect accordingly.
But it still is a sanitary principle to reflect occasionally on the basis of one's hypotheses.
How much of panspermic correspondence, speculation and spittle could justifiably be dignified as "astrobiology", I could not say, but, for the most part, I do not pretend to be favourably impressed so far. It is not that the participants are stupid, but there is a feverishness, a partisanship, that drives many participants to take offence at observations of empirical and technical fact and logic, and to leap on any and every new bit of evidence, be it never so ambiguous or immature, as complete vindication for naïve Panspermia.
There is precedent for such attitudes of course; they have been characteristic of religious strife for millennia. I am lucky not to live in an age when dissent meant burning at stake.
A few views with room
I tolerantly concede that the alien-spore hypothesis does provide scope for argument that exotic origin provides more space and time in which life may have evolved, but as I shall show, firstly that is nothing like as persuasive an argument as its proponents would like to think, and secondly some of those very proponents argue that practically every rock in space or on Earth plausibly contains living microbes. On that assumption it is by no means clear that a long time is necessary for abiogenesis in the first place. What a pity that Pasteur did not extend his experiments for a few hundred years longer and work on rocks, rather than broths!
Such concepts could be pilloried as apparently absurd, but in science common-sense rejection of proposals merely on the basis of their apparent absurdity is not cogent. In fact commitment to a diagnosis of absurdity has a history of leaving illustrious scoffers with egg on face. Accordingly I make very little play on the intrinsic absurdity of Panspermia in a steady state universe, but hope to show that the concomitant concepts, quite apart from their current unpopularity among cosmologists, lead to far greater logical and biological difficulties than any that they purport to solve.
So far so good; many a field in the most pedestrian of scientific disciplines has housed schools with radically differing views, without bringing the entire field into disrepute. Cosmology is one convenient example! Accordingly it would be unreasonable to demand uniformity of views among panspermists. But I hear warning bells. In particular, in Panspermia, as in many fields of pseudo-science, warriors from both extremes will skip nimbly from premise to premise and back again when they find themselves under pressure. Professional scientists who would strip the hide off any student who tried to argue on the basis of inconsistent assumptions, will quibble like lawyers. They forthrightly start out with a specific proposal, then under pressure they retreat into hand-waving. Having strategically retreated before the immediate objection, they sally out again even further on the strength of such pressures not having routed them from the fastnesses of their vagueness. In their new-found confidence, they then duly demand precision from the opposition. Unfortunately, and with good reason, they do not as a rule settle on some middle ground of significant claims and practical research proposals.
Responses to recent reports of putative bacterial fossils in meteoritic or Martian material that apparently had been subjected only to mild forces and temperatures, are typical (to my jaundiced eye, anyway!) To hear the panspermists, you would swear that they had found a live dinosaur hatching from the rock! Chandra Wickramasinghe is quoted as explicitly speaking of the results as "vindicating Panspermia". Well, perhaps I should not be too critical; among the zealots such a remark is about par for the course. More assertive proponents do not teeter timidly on the brink with terms such as "vindication", but plunge directly into asserting the continuing effects of panspermic injection into terrestrial ecology and evolution.
Speaking as an observer rather than a participant, I diagnose the inconsistency and the basing of large claims on small evidence, as symptoms of exigent hard data. When a logically coherent structure of observations is available, it makes it easier both to stick to a definite position, and to pin an opponent down instead of continually having to retreat from generalisation to glorious generalisation. In contrast the style of typical defences of Panspermia strikes me as irresistibly reminiscent of the cold fusion proponents. In established practical disciplines with clear theoretical structures and large bodies of data, fringe partisans have a far harder time of it; if the data support one, one needn't skip and if they contradict one, there is little scope for skipping.
Not that that always stops the fringe!
All this is Good Stuff. Science would make pretty lame progress if we did no speculation, and a bit of bite in the debates adds zest. After all, no one forces the gentler spirits among us to participate. Anyway, proposal and criticism of new ideas keep the livelier among us alive and hone our ideas, and if it annoys pedestrian fogies to see us at play, well, a little sorrow is good for their character and they can console themselves with their customary derogatory grumbles.
But a good slanging match is no substitute for soundness and in science argument without soundness soon palls; there is too much real work that can be done instead, and done more rewardingly.
At the modest end of the scale, almost the main point of interest that I see in the oligospermia version of the Panspermia theory, if the hypothesis of effectively unique inoculation of this planet is true, is the implication that somewhere away from Earth, life has evolved and that such life should have certain aspects in common with life on our planet. That fact would seem tremendous enough in its own right, and if we had the faintest clue as to where to look for the source, it would justify serious investigations and attempts at a visit or at least at sending some probes. But for the fundamental theory of biology on Earth itself, its implications seem pretty slight to me. It would be largely the comparative biologists and students of process, such as the evolutionists, who would have a really practical interest.
For one thing, as things stand such a hypothesis is practically unfalsifiable. For another, it is not at all clear that its implications for terrestrial biology entail predictions different from the reigning hypotheses of abiogenesis on Earth. It is hard to imagine how it suggests any change in our view of work that is already established or underway. Even less does it suggest anything of Earth-shaking philosophical significance. Ask yourself: either a germ lands in a lifeless, nutritious soup, and prospers, or a similar germ assembles out of that soup in much the way that the invader germ might have done on another planet and prospers. Philosophically it only makes a difference of one remove in the origin of the chain of life. In fact, for all we know, Panspermia might be true somewhere, but with Earth as the source planet!
The problem is not the intrinsic implausibility of oligospermia, but the intellectual futility of attempting to prove a negative. We have no shortage of theoretically possible, unverifiable propositions without any special evidence to favour them over simpler hypotheses. This does not mean that the simpler hypothesis is right, Occam's razor is a working principle, not a proof, but it does imply that if we prefer the less parsimonious hypothesis, we have work to do before we can achieve cogency.
To be sure, there are plenty of other lines of research on which related astrobiological questions could piggy-back: the study of our solar system and of "nearby" stars; the search for extraterrestrial intelligence; the investigation of the radiation profiles from our neighbouring regions of space; the nature of our own molecular biology; and so on. All of these have their own justifications on their own scales and some of them might point us in directions where we do find a justification for a study of Panspermia, or at least polyspermia.
But so far, so nothing much.
A Little bit More and a very little bit Less Doubt
I trust I have now made it clear how nearly dismissive I am towards oligospermia, so now let's see how much more promise there is in polyspermia. To my mind polyspermia would have little more day-to-day biological significance than oligospermia, once life got established. There is not much in the line of biochemicals that you can drop into our biosphere in nanogram quantities nowadays without it being gobbled up by incumbent organisms, or indeed, getting inorganically oxidised, hydrolysed, or otherwise degraded. Anyone who has tried to culture viruses and knows how fanatically one must exclude microbial predators and decay organisms, will take the point. Injections of "living" biochemicals on the order of once per century or less are most unlikely to make a dent in our biosphere. Proponents of polyspermia would have to produce something substantial and falsifiable to make the proposal interesting.
In science a proposition doesn't have to be false to be boring.
In fairness, since I wrote the foregoing, the Stardust Cometary and Interstellar Dust Analyser has made observations consistent with encountering (literally) a few large polymeric heterocyclic aromatic molecules in space. That is in its own right very interesting, but not really surprising, in fact damply underwhelming so far. So we have either an unreliable detector on our hands, or tarry soot molecules in space? Hands up anyone who cannot think of half a dozen possible explanations on the trot; explanations independent of biology in general and Panspermia in particular, several of which would be reasonable prospects for further investigations.
Sir Fred Hoyle and associates proposed that the molecules could be the debris from collisions with microbes (the quote I saw said "bacteria", but I'll not hold anyone to anything as Quixotically specific as that.) The proposal is reasonable, but not persuasive as yet. Before I would be willing to take it seriously, I should want to see some work on the signatures of collisions of freeze-dried bacteria with such collision plates and comparative studies of collisions with other organic molecules or scraps of graphite. I am sceptical... well, let us say "reserved", about collision-cracked bacteria giving such a clean signature so fast after the collision. If tar were to be the end product, I should expect a fireball of more volatile material first, with large tar molecules forming on more leisurely time scales, probably long after, perhaps even milliseconds after, the space craft had passed on.
And if the signature did match bacterial barbecues, then any scientist worth his salt should be asking about alternative explanations before plumping for specifics.
Wickramasinghe is quoted as explicitly and specifically going further with claims such as that comets are the breeding sites for cosmic bacteria picked up from interstellar space to incubate them in their warm watery interiors. Apparently, having exhausted the comet's heat source, the bacteria become dormant and may enter the Earth, for instance to establish the Archaea. (No doubt the Eubacteria are then to supposed to come from Mars...)
Close followers of on-line Panspermia material will probably recognise the source of that précis. And if their reaction is anything like mine, then, given such a level of speculation and assertion, they will be long way from getting excited about the panspermic implications as yet.
Another line of objection might be: "So it may be just nanograms per century; so what? How many nanograms do you need to convey a germ? You could get quite a few typical bacteria into a nanogram of medium. What if it is a strain that can survive under ambient circumstances and in fact take over?"
Like the Tooth Fairy, this is a line I cannot refute in cogent terms. But like proponents of the Tooth Fairy, polyspermists should beware of basing too much hope on that. Plausible circumstances out in space are not much like those on earth and the doctrine of microbial infallibility implies among other things that wherever you go on Earth, there will be germs and they will be better adapted to their niche than the invaders. The doctrine may be humorously expressed, but its basis is serious. All our indestructible hot spring and ocean vent archaebacteria would survive poorly if splashed anywhere into the pelagic ocean, say. They would be plankton food, chop chop.
Whole strategies of management of epidemics and ecology are based on the principle that you can suppress or even wipe out an invading microbe if you can encourage incumbent micro-organisms to compete with it. Think about that as you add yeast to your home brewing. Think about it as your body assembles leukocytes about a festering sore.
As for the probability that the invader might happen to be qualitatively indistinguishable from indigenous life forms, sorry, try the other leg. In my undogmatic, but considered opinion, that is about as likely as their talking English. Bacterial in physical morphology I could understand, but matching biochemicals? Try next door!
By this time disgruntled panspermists might well be asking: "First he wants evidence and then when he gets it, he ridicules it! Just what WILL this guy accept as grounds for changing his mind?" I refer them to the Appendix for a rough indication of the kind of attitude I try to take in such matters.
Well What about the Interstellar Sea of Life, then?
As for Panspermia proper, in a steady-state (or at least eternal, or at even less than least, a very, very long-lived) universe, eternal omnipresence of spores could serve as a steady-state presence of life, a sort of diffuse, cosmic, eternal ecology.
In this range of theories things get messy. The range of possible significance and of sources and effects is too wide for comfort. The upper limit of density of interstellar life might be some function of the observed opacity of the interstellar medium. We could be sweeping up a continuous thin drizzle of life on our path through the universe. This version of Panspermia is the main playground of the purveyors of cosmic sources of diseases, for example, and that would peg the lower limit of ambient life at a frequency related to the frequency of new plagues on Earth. This would imply that it be worthwhile to hunt for such spores and test for the nature of their viability in space and on earth. Unfortunately, negative results rapidly tail off, first into polyspermia, then into oligospermia, then into unfalsifiability: So you did not find anything? Obviously you did not look long enough and hard enough (One virus is all you need in this sort of argument, to start an epidemic, no matter what spoilsport virologists say, and how do you expect your filter to pick up so low a frequency of particles?) You did not look in the right places. You looked for the wrong things (who says flu germs in space will be in the same form as flu germs in eukaryotic host cells?) Your device was not gentle enough; it destroyed the specimens. Your tests were not diagnostic enough to recognise alien organisms. You did not recognise them even when they were patent; and what price the obvious bacterial fossils that you have been overlooking in Lunar and Martian rocks?
And so on. To make things worse, even on Earth it is no easy matter to detect or identify really microscopic life forms or quasi-life forms (such as viruses or viroids). Even when one actually has a fair amount of material at one's disposal, there can be a great deal of argument about the nature of, not only fossils, but say, putative extant soil or gut or atmospheric microbes. Believe me, when one looks through the microscope, one does not immediately see all those beautifully labelled pictures of cell walls and double helices. Such obliging identifications are artefacts of modern textbooks and coffee-table books.
In general, in practice, proof of a negative becomes very, very difficult and often so does demonstration of a clearly diagnosable positive.
As a rule mere failure to prove a negative only constitutes cogent proof of a positive when arguing with suckers. Fortunately for purveyors of snake oil, suckers are in plentiful supply. For the rest of us however, failure to prove a negative should fit into a persuasively comprehensible conceptual and factual framework before that failure is seen as strong support for a positive. Personally I would not regard any single putative source of microbial fossils as strong evidence in any really crucial dispute; too much is dependent on interpretation of debatable effects of putative and ill-defined causes. This means that bacteria-sized nodules in a few meteorites for instance, are very unlikely to be convincing of anything. Their only real value is as confirming instances and as establishing upper limits of the possible frequency of bacteria in alien material.
Am I not being unfair? I do in fact accept that there are correctly diagnosed bacterial fossils three of four billion years old; how dare I selectively accept that, and reject the evidence for bacteria in exotic material? The difference is that although I guess that much of the Earth material is wrongly diagnosed as well, there are vast volumes and varieties of terrestrial material and they form disputable, but broadly comprehensible patterns consistent with a plausible development of biology and ecology on the planet. This leaves room for a great deal of error without invalidating the gross vision and offers scope for controlled studies. Residual errors are not of sufficient importance in such a context for me to take a detailed interest; I am no micro-palaeontologist! Where claims become less plausible, I become more churlish about accepting them and demanding controls. For instance, I am already a bit suspicious of some claims of bacteria being identified from a full 4e9BP. Whether the error is in the diagnosis or in the dating, or in my own suspicious attitude, I cannot say, but the point is in any case that I am not equally receptive to all diagnoses of petrified bacteria and do not claim to be equally well justified in all my acceptance and rejections of, or demands for more, evidence. Recent suggestions that life might have survived the awesome bombardment of the accretion phase of the planet by being blasted into space and descending again once the all clear had sounded, strike me personally as being too speculative to be interesting at present and in principle as being of little practical relevance. Either that life had originated on the planet, or not. If it had, then Panspermia had played no role anyway and the only point of interest would be that indeed, microbes might survive blasting into space and subsequent re-entry. If the life were of exotic origin, say from accreting material such as comets, then where was the interest? Had life-bearing comets run out of stock in the mean time?
In the light of such attitudes and arguments, I consider it only reasonable for me to demand a good deal more control evidence for microbes, living or fossilised, in meteorites, moon rocks and Martian material, not to mention the high stratosphere. In this last example the controls are different from the rest and would deal with the nature of the microbes, their provenance and survival, rather than the implausibility of their existence or genuineness.
Problem of scale in Earth as it is in Heaven.
One example of contorted reasoning is that Panspermia relieves us of the intellectual burden of the improbability of getting a vanishingly improbable protein (or nucleic acid chain or the like) in the ridiculously short time and space estimated to have been available during the period of abiogenesis on Earth. (Perhaps a few million or hundred million years.)
This is only persuasive if it is relevant, but in fact it is a mouldy old chestnut, not too appetising even when it was fresh (if it ever was; I suspect it to have originated somewhere in a steady-state panspermic universe.) There is no persuasive evidence that probabilistically independent selection of monomers for assembly of effectively unique target chains ever would have been relevant in the genesis of life. In fact, if only the panspermists would listen for a little while, they would realise that that mainstream molecular biologists have for a long time been wearily explaining that that point is common cause. A reductio ad absurdum is a pretty silly thing to use against an argument that the opponent never espoused and never would have dreamed of defending.
So, there is no point to arguing about 1e-137 probabilities (or whatever ridiculous figure one prefers) of generating a particular molecule, for example. We have fairly comfortable theories and experiments to suggest that promising-looking classes of molecules might be expected. The relevant question becomes, not whether we get some particular molecule, but whether we might expect any viable molecule. For all we know the frequency of viable macromolecules in the space of accessible products on our ancestral abiogenetic planet, might be of the order of one in millions or billions, rather than one in googols. That would be ludicrously high.
Macadamias, Monkeys and Combinatorics
Let us consider a rather laboured analogy: put me down in a wilderness with nothing but water and macadamia trees with their ball-bearing-like nuts for food. Unless I can crack the nuts, I shall die hungry. Trust me if you don't know wild macadamias: you will NOT crack them with your teeth! What is to hand? Only stones. I am doomed! Think of all the shapes, sizes and textures of stones that one might get: not one in gazillions would be remotely suitable for cracking those incredibly hard nuts! For one thing, by far the largest number are hopelessly too small; they are so predominant that we don't even call them stones as a rule, any more than we call codons nucleic acid chains. We call them sand, gravel or pebbles. And yet technically they are stones, containing say, 1e4 to 1e24 atoms each. Of the larger specimens, many are too heavy to lift or too crumbly, or badly shaped, only good for rockeries or for smashing fingers. Obviously I am doomed! Only one stone in perhaps a trillion is any good. I will starve long before I inspect a trillion stones, even at a billion stones per day, say ten thousand per second!
And yet, bad luck folks! I do survive! You find me after a year or so, morosely cracking my seventy thousandth nut or so and cursing food that at first had tasted like ambrosia. I have a neatly shaped anvil and a comfortable hammer of rock, very well suited to the job.
Now, in my wilderness there are something like, say, 1e18 technically accessible rocks. I have found just these two; the probability of finding not just one, but both is obviously about 1e-36. Very, very poor odds! Nothing could realistically explain my survival, unless I have been visited by aliens who supplied me with those two rocks. How feeble sounds the objection that there are say, 1e9 suitable rocks in my wilderness, and that I neither am limited to this particular pair, nor did I have to go through 1e9 candidates to find them, nor even are they the most suitable rocks in the wilderness for cracking macadamias. They are merely the first ones I happened on and retained and possibly modified in use. In fact, if a stream ran through my wilderness, I might find suitable rocks by the thousand in its bed, concentrated, largely pre-sorted and ready to hand.
Have I now laboured that point to sufficiently mind-numbing weariness?
Analogously, of all possible macromolecules that might occur in our planet's pre-biotic soup, not just a few nearly unique molecules, but a very generous proportion, may have been promising prospects for the development of some form of life and they might have been concentrated where they were likely to meet complementary molecules suited to corresponding biotic functions. There were many conceivable pre-sorting mechanisms, ranging from surface tension effects and fluid interfaces, to adsorption on suitable minerals.
In such circumstances the required degree of specificity of which molecules were needed to generate life, may not have been very demanding. Modern life forms might demand firstly, specific molecules. Secondly, they might demand greater precision and efficiency of their molecular structures and mechanisms, than we could expect in our seminal, transitional biological products. A single codon error can mean the difference between say, sickle cell anaemia and healthy haemoglobin. But such modern sophistication could be the result of a few gigayears of subsequent, devastatingly effective, heuristic adaptation during the period since the original limping abiogenesis. Analogously, it would be hazardous to argue that Palaeolithic tools could not possibly have been useful in the past, because they are dangerously useless in a modern machine shop, where imprecision of a millimetre or two would often be disastrous. And the process of evolutionary adaptation is heuristic as opposed to stochastic. Anyone who does not know the implications of that has a lot of homework to do.
While we are on about clichés, let's speak of monkeys, monkeys with vast stamina and a huge supply of typewriters, very, very good typewriters with lots of consumable supplies. After something like 1e1e7 keystrokes (sure; call me a liar for the sake of a few googols!) we get a complete Shakespeare, right? Maybe. (With MY luck, don't rely on it!) OK, but what else do you get on the way? Any half Shakespeares? Any other full Shakespeares in different sequences? How about a few trillion partly misspelled Shakespeares? What? Not even a Pushtu Limerick? How about a few Spencers, Schillers, Semmelweisses or Skytbalies? (Skytbalie never actually existed, but he is the fellow who would have written the definitive, cogent explanatory treatise on the nature of mind, its generation and predictive physics, if only he had in fact existed. His work would have made Einstein look like Enid Blyton for depth and like a nineteenth-century political-theoretic tract for clarity and cogency.
Unfortunately, if he *had* been real and he had gotten round to writing it, the non-existent Skytbalie would have written it in his non-existent mother tongue of Strondskrif, so no one could have read it, since we have no such language. However, this tract may have appeared in the by-products of our monkeys' output, and maybe there would also be a fortuitous dictionary... into the other non-existent language of Gageluid!) See? All that Good Stuff may be cramming our monkeys' output and we are not even assuming anything heuristic about their typing. Looking through that mass for a long, long, long time, we would in due course find the Shakespeares and Schillers and so on, while in another universe these would be sifted out unrecognised by the delighted Strondskriftish and Gageluidish in their exclamations over the Skytbalie tracts.
In short, a random text may have a low, a vanishingly low, probability of containing a particular text we are seeking for in a particular form, but it might have a very high probability of containing something meaningful, possibly material we are not equipped to recognise, and in a form we are not equipped to recognise.
We have no way of knowing what the frequency of meaningful RNA, DNA or peptide chains may be within the space of accessible sequences, combinations and configurations in our planet's prebiotic soup. Meaningful in this sense means something like "interacting as functional pre-biotic or actual biological components" even if there are many other such meaningful sets of components such that the sets are mutually meaningless.
But we can be pretty confident that our original ancestors were just one or a few possibilities out of a vast range of functionally viable molecular configurations. How many of those could in principle have evolved into life indistinguishable from ours, is a question we are nowhere near resolving, but it would in principle only have needed one, or at worst very few. My personal bet is that many different ones could, but that far larger numbers that could never have evolved directly into the likes of us, could have evolved into other life forms that we at least would recognise as life. Some of those might have done vastly better than ever we could, some might never have got beyond the slime stage, but I happen to be a member of the contingent school of evolution and I believe that if life were to start off with identical molecules on a million identical planets, no two would evolve particularly similarly. The descendent life forms would differ even at the biochemical level.
Be that speculation as it may, tell me why I must be wrong to guess at frequencies of one such "meaningful" molecule in millions or billions of molecules overall. Those would be very high frequencies, implausibly high. It would mean that on a suitable pre-biotic planet, vast numbers of potentially viable molecules would be generated, each just needing the right "reader" of its "meaning". In our monkeys' output, if Strondskrif had indeed been our language (and who are you to say it is intrinsically a lesser probability than English) then Skytbalie's works would have been far more recognisable to us than Shakespeare's and it would be Shakespeare's writings that would land on the scrap-heap as meaningless.
In our pre-biotic soup, in contrast to the monkeys' text, we are postulating a massively polyglot, mercilessly impartial searcher through a wide range of candidate molecules; any articulate output in context, in any language, potential or actual, could be recognised.
Our searcher is Reality.
Reality's criterion in scanning for readability is simply that what works is selected. If more than one works, both are selected for as long as they work, until they clash, and from then on it is a question of competitive or co-operative natural selection. It is not that any one outcome is demanded, nor that it should be in any particular language, nor even that it be the greatest text, the most effective living or pre-living mechanism, but only that it works in actuality. In short, it might easily happen, if the original abiogenesis was not in fact particularly unlikely, that many planets have biochemistries basically similar in principle, but drastically different in detail from biochemistry on this planet and totally functionally incompatible with it.
But back to the typing. Would a particular work, specified in advance, say that of Shakespeare, really be of any value in such a gravitationally disastrous mass of material? Definitely not. We could never find it as our particular target. Our magical scanner, Reality, has a heuristic aspect to its action. It does not search for any one target; it does not even search for any present potential target; it "searches" first for a target, superior or inferior, that happens to emerge and to commence working effectively, or at least marginally effectively. Once that has happened in the ancient soil and water, far more specific and much faster and more efficient heuristics govern the subsequent process. In this respect the incorporation of stochastically generated molecules into functional pre-life structures is conceptually heuristic. (But NOT teleological! As you can tell, the distinction in such a context is subtler than one might have guessed.)
Heuristics in Space
An important point, a vital point that most panspermists that I have encountered so far are prone to overlook, is the concept of the non-necessity of comprehensiveness. Our pre-biotic soup or sludge does *not* contain all possible candidate molecules; it does not even contain a trillionth of a trillionth of the accessible range of different molecules. There is no need, or we would not be here. We neither endow nor burden Reality with the comprehensive range of target molecules to select any one target from. Our entire observable universe, *not* just our planet, is far too small for so much raw material to search through, and if it were not, the probability of all the molecules necessary for coming together into a uniquely prescribed organism would be exponentially smaller still; in a word: absurd.
We do not get a go at such beyond-astronomically huge numbers of molecules, but then, as I said, we do not need to; on Earth we get perhaps a few trillion tonnes of job-lot precursor molecules juggled in muck or on clay for a perhaps few hundred million years, giving some minute subset of the possible combinations of the members of that minute subset of possible molecules a chance to strut their stuff. Maybe many structures do promising things, maybe only one ever does. But none will ever do anything useful out of context. Most of the molecules that would not fit the emerging templates simply never arise. (Come to that, nor do most of the molecules that would fit!) Any items that together with their neighbours do mutually "mean" anything constructive, get a chance at a new, possibly an improved, generation.
And that is where the heuristic aspects come into their own. This sort of functional context is a demanding requirement in such a connection. We might as well forget about getting a really effective design first time. We need trial, error and constant improvement, possibly through thousands or millions of generations before we have a recognisable cell. This demands all sorts of transport and energy problems, to move the parts and their "foods" towards each other as required.
No recombination or no interaction: no heuristic feedback.
One of the greatest problems with any space-based abiogenesis as opposed to planet-based, is that it is exceedingly difficult to create a persuasive scenario for that heuristic feedback. On Earth we luxuriate in a supply of lots of water for hydration, support and transport, lots of clay particles for anchors and templates, a wide range of environments of different temperatures and chemistries, high mobility and a good turnover of raw materials, with constant encounters between organisms or molecules. In space you would be lucky to get a single peptide, let alone a virus. And if you did miraculously get a virus, what meta-miraculous procedure would generate another virus of the same kind in the same region, or move two of them together if they happened to be generated a few metres apart?
Sir Fred Hoyle has been characteristically ambitious in proposing "Black-Cloud"-type assembly-line systems, and he certainly has been both the most entertaining, creative and impressive exponent of such ideas, but really, they all boil down to hand waving and SF. There is no prospect of any heuristic space-based generation of proteins, let alone viruses, within ten orders of magnitude of the rates easily accessible on a water-rich young planet a suitable distance from a young G-class sun. Wickramasinghe's comets with their warm watery interiors are fanciful in comparison. It seems to me just a little demanding to expect an internal ocean in a snowball a few kilometres in diameter. Of course, I am indulging in a cheap shot; his model is likelier to be something like a portion of the "snowball" turning to mud when supplied with enough warmth.
For his next trick I should like to see his model for mobility of mud or within mud in microgravity, particularly in comparison to mud in tidal or turbulent planetary oceans. Either his comet is in a characteristically highly eccentric elliptical orbit, with only a few months of warmth every century or so, or it spends a lot of time near the sun. (All right, it also could simply skulk in the Oort cloud, but I have little faith in solid-state frozen abiogenesis!) A comet in a permanent warm orbit would lose its volatiles in a couple of million years at most, or more likely a few thousand; hardly a promising place or period for a few tonnes of slush to generate life! An intermittent sun-grazer would effectively have the same period of promise, except that it would divide its dolce far niente into summer holidays spread over a longer total duration, but hardly any longer effective opportunity for biogenesis.
Wickramasinghe', to do him justice, does not seem to assume that the comet's internal energy supply, however speculative it may be in nature, lasts indefinitely. Nor does he in anything I have read, assume any significant photosynthetic or other energy supply of solar origin. Not all his supporters are equally cautious. Some wield dreadful verbal clubs like "autochemolithotrophic" with ghoulish relish, in apparent faith that they will so intimidate anyone who cannot excogitate such esoteric etymology, as to insure the sesquipedalians against objections such as that not every mineral offers usable negentropic opportunity for driving living metabolic processes. No matter how long the word, if one lacks dissipative energy levels, one cannot power life.
And one example of autochemolithotrophic barrenness is rock that has already been processed to completion in its given environment. On a planet this is not necessarily a death sentence to an ecology, because there is generally a prospect of a change of ambient conditions. For instance, once anaerobic processes have exhausted carbon and sulphur resources and converted them into hydrides, sulphides or elementary form, gravitation, erosion, diffusion or tectonic movements may expose the residues to oxidation and the release of more energy than ever the anaerobiosis ever released. What would the cometary equivalent of that be, once any process had gone to completion?
Please note my own hand-waving and have mercy on the freedom my assumptions. I have performed no calculations to support, for instance, "ten orders of magnitude" and I do not intend to try. In fact I see no prospect for any heuristic space-based abiogenesis at all, but "orders of magnitude" sound so impressive, and I would love to see what precise figures the panspermists would undertake to defend in rebuttal!
And so, when it comes to diseases from space, those monkeys of ours, in spite of their low productivity, do leapfrog over some serious obstacles, such as the question of the medium in which they produce their output. If anyone gave me a scroll with all of Shakespeare in it (or even a single sonnet, actually) and tried to convince me that he found it in a virgin rock from outer space, I'd want some fairly persuasive supporting evidence. All this and in English too? Elizabethan English? And on paper? A single glucose molecule or an etched rock from space I just MIGHT swallow, but glucose polymerised into shredded cellulose, compacted and sized in space? Or splashed off another planet on which cellulose just happened to be the available substrate? All this without heuristics?
Well, that is something like what panspermists are in effect trying to sell us in the form of diseases from space. Please note that a virus is not just any ball of protein and RNA; it is a structure of not only the right proteins in the right configurations of the right lock-and-key conformations, but with the necessary lipid bilayers, the right enzymes included inside, and the right RNA chains inside with them. Just TRY assembling anything of the type except in a liquid aqueous medium, using the necessary assembly machinery! In fact, a lot of disease viruses die if you so much as desiccate them. Anyone who thinks that he can generate flu viruses just by shaking the ingredients in water (never mind in a comet), good luck to him for the first million years or so. Apart from the problem of finding just any biological "meaningful" molecules, we also are demanding that what we get should be functionally compatible with terrestrial hosts! This combinatorially raises the threshold improbability to ridiculous levels unless the panspermists can show that there are at most a few different ways in which life can in practice evolve in space and that those ways are very accessible (except on Earth of course, where we are cannot generate our own novelties and so are critically dependent on imports from space).
In short, instead of just ANY "Reality Selected" molecular structure , we are right back with the original problem of demanding a particular target, or at least a very narrow range of targets, (which I once again remind you, is absurd).
Translate all this into engineering terms: it amounts to asking for the proverbial whirlwind to assemble a Boeing out of a scrap yard, instead of in a machine shop with all the ready-made components to hand (or to eddy.)
What is more, it is like asking for a Boeing and refusing a Handley-Page. Of heaven knows how many possible viruses, we get, not just any virus look you, but an ordered sequence of strains of viruses of middle-of-the-road complexity and specificity to a modest subset of vertebrate hosts. For our miraculous virus from space to have just the right neuraminidases and haemagglutinins is asking too, too much.
What is more, we do not get persistent polio or rabies epidemics from space, it seems, though both of these viruses are quite infective when they get into respiratory tracts or the eye. And what price smallpox? Has it gone out of interstellar fashion, now that we have exterminated it in the wild? No, what we get is colds and flu, especially flu, and the flu in particular, we get for epidemic after epidemic, following well-worn pathways from the East. Obviously our celestial plague factories are fussy, not only about which viruses they assemble (by no means the simplest please note!) but also about which landing fields they favour!
And the sequences of new epidemic viral strains every few years just happen to be logically consistent with Earthside evolution too? With due respect for the feelings of the Creation Scientists, evolution down here has not yet stopped, you know!
Sex and Sterility in a Closed Universe
Our Universe is Small, Small, Small
Now, while on the subject of evolution, apart from such pedestrian claims as space as a source of disease, some schools of panspermists argue that besides the original events of abiogenesis, the very continuation of evolution on our planet is inconceivable without regular injections of evolutionary advances. You see, these schools claim, typically invoking thermodynamic principles in support of their views, that evolution just is not possible in a closed system. After all, decreased entropy is impossible in a closed system, isn't it?
Well, it might or might not be globally impossible for all I can tell, but the conclusion is a gross non-sequitur. For one thing, one certainly can get local decreases of entropy, such as the local formation of crystals within a closed system. Within a strongly dissipative system, for example a watery planet perhaps 140000000 km from a G-type sun, the localised decrease in entropy can be quite startling. There is a weary observation, if ever you saw one! Similarly, one certainly can get local evolution at a high rate, while in other regions, apparently similar, not much happens. But special pleading is the stock-in-trade of the fringe scientist; thermodynamics, it seems, is no problem to micro evolution, but absolutely forbids macro-evolution!
Pardon my yawn; déjà vu gets me that way and this subject is weary. Weary!
In any case, the analogy of evolution to thermodynamics and its relation in general to thermodynamics are treacherous, to put it politely. Evolution is simple in concept, but it bristles with intellectual traps, and nowhere more than in the context of thermodynamics.
Still, however all that may be, this panspermic argument has its attractions. After all, just because we could get by in a closed system, does not mean that we could not profit from continual enrichments of our gene pool from a universal, eternal ocean of infinite genetic variety and indefinite honing of functionality, does it? Who am I to say that crucial phases of our planetary evolution since the original abiogenesis, phases such as the development of eukaryotes, of multicellular life, of cellular differentiation and organisation, of nervous systems, motility, limbs and lungs, of speech, technology, nukes and flu, should not all have been derived from our bounteous intergalactic flux of universal biogenicity?
Almost I convince myself...
And yet, as I promised to explain, the persuasiveness of such views is not proof against a little innocent questioning. The ideal panspermist of this school likes to ignore the enraged screams of mainstream cosmologists and assume a steady state universe and steady state life, but for our planet, he is happy to accept an age of some 4 or 5 billion years.
Now, even taking that steady state universe for granted, are we or are we not in an open system? Ideally perhaps, but not actually, and certainly not effectively. In all our history we have never interacted with anything more than 4 or 5 billion light years away (strictly speaking, half that, and even then such interactions have not been of much relevance to Homo sapiens!). Let us call a sphere of radius 5 billion light years our observable universe. Actually I am being hopelessly generous, but in any case, a 5-billion-light-year sphere is not an infinite space. And it remains finite and closed, no matter how infinite the surrounding steady state infinity may be.
Not much of a limitation you say? As a matter of common sense, a sphere of that size will do for infinite? Well, actually not. Finity can be very big. Consider the favourite argument as to why the open universe makes a difference: the Vast numbers of possible macromolecules one can get, of which only one is good for anything. (Using the capitalised "Vast" in the sense that Dennett coined.) A 1000-amino acid peptide, ignoring the various configurations and modifications possible, can comprise any of about 20 to the power 1000, or roughly ten to the three thousand different amino acid sequences. Now, ignoring gravitational collapse, our observable universe should have something like room for about ten to the 77 such molecules, packed solid, if the back of my envelope does not need new batteries. But the point is that even if my calculation is out, not by a few orders of magnitude, but by its own square or even cube, that hardly dents the space required for so many molecules.
And that is only for ONE protein!
And beware of invoking interactions with even vaster stretches of space, from molecules that entered our sphere 5e9Y BP after travelling a few trillion years in advance; if they *did* include all the molecules we need, stochastically generated, there *still* would be no room for them in our observable universe!
That argument therefore collapses ignominiously without the benefit of gravitation.
No. Stochastic generation of specific molecules is out! Either the search space is crowded with viable prospects, or we are left with heuristic or teleological origins. The latter lead us straight into first-cause theological arguments, which I ignore in this discussion, while heuristic arguments are the very stuff of Darwinism.
Terrestrial Darwinism at that!
In short you can *forget* about the brute force approach to solving the macromolecular combinatorial problem. The steady state universe not only does not solve it, it does not even get within radio telescopic distance of beginning to get to grips with it. We are not dealing with big numbers here. We are not dealing with astronomic numbers. We are not even dealing with cosmological numbers. We are dealing with what I speak of as mathematically inconvenient numbers: nothing you can do with them relates sensibly to our world.
So, give or take a few dozen orders of magnitude, we are in just about as closed a world, relative to realistic molecular options, whether we can exchange genetic material with the Andromeda galaxy in our backyard, or with the most distant quasars we have ever inferred. The difficulty of getting just the right molecules from throughout the vast reaches of space, is for practical purposes as bad as if we had stayed with our feet chained to our own little ball of Earth.
It also should give the steady-state-life partisans to think furiously about just what the spread of life throughout the universe actually means.
Let us think about it.
You Can't get Here From There
In fact the sheer size of our small universe makes nonsense of any proposal resembling a general equilibrium mix of approximately uniform life particles, even though I have been far too generous. If we are to accept an effective range of 4e9LY in 4e9 years, then we are assuming that the seed material got accelerated to nearly light speed (how?) without destroying it (how indeed?) and without striking anything en route. If collision en route were a factor, we should be getting a lot of as yet unexplained hard radiation from space. (Gamma ray bursters, perhaps?)
Then when the near-luminal life parcels reach us, they decelerate harmlessly (how once more?) to land harmlessly in a receptive spot. Not only that, but they keep doing it year in and year out for billions of years?
Patience upon a monument...!
More typical drift speeds are something like four or five orders of magnitude slower than this, and the accessible sphere of sources of infection accordingly reduces to some hundreds of thousands of LY. So we would be well out of reach of Andromeda. In fact, the hundreds of thousands of light years thumb-suck is pretty optimistic -- something of a mathematical upper limit. A more plausible radius for practical purposes would fit comfortably within this arm of our own galaxy, not much more than what seemed to constitute our universe at the start of the twentieth century!
And given modest drift speeds, we still could expect serious problems fielding biomolecules in our atmosphere. Consider: an unprotected DNA molecule in space would need stunning luck to survive the ambient UV and shorter ionising wavelengths for long, never mind for millions of years. Nucleic acids are very UV-sensitive, remember? Next, though proponents of Panspermia argue that an atmospheric landing at escape velocity speeds would be gentler than capture by orbiting samplers, I would love to see this supported by more than bare assertion.
Alternatively, we could have the nucleic acids as inclusions in accretions, protected from UV, (though not equally well from X rays or gamma rays, or from energetic particles, which are bad, bad news for nucleic acids on earth, though it seems that we are to neglect them in space!) But then, how are we to field the cosmic gravel on earth? Such as I have seen has vanished as incandescent vapour and dust in the stratosphere. Is the nucleic acid supposed to survive that?
But, someone pointed out to me, simple inclusion of living spores in the centre of rocks some tens of metres in radius would protect them from interstellar radiation. Well yes, silly of me... But for how long, I wonder? Where I come from, one does not simply cut off hard radiation with barriers, one attenuates it. Now, if that rock is somehow supporting an ecology on its multi-million-year trajectory, its occupants could in principle protect themselves by expending resources on repairing radiation damage, as some bacteria, most notoriously Deinococcus radiodurans, do. Incidentally, there seems to be a meme for misspelling it "Dieno..." But that is being greedy. It is challenging to construct a scenario for such a rock with such an ecology and still have it land without converting its entire mass to oxides and tektites. Furthermore, bacteria do not simply resist hard radiation as a matter of routine, any more than they resist heat. If it were otherwise, heat and radiation would not be such excellent means for disinfection, which, trust me, they are! Those that can do it, are the ones that could adapt to it by routine natural selection.
So we also need a scenario that includes adaptation of our microbial voyagers to hard radiation as well as to hard landings!
It is a small, lonely, closed universe! If we want company, the sooner we develop an FTL drive, the better!
... and Two smoking Barrels
I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favour to men of skill; but time and chance happeneth to them all.
Another approach is the shotgun. It works for weddings, doesn't it? So I'm told.
It doesn't work in science, not as a substitute for sense anyway. One correspondent assures me that we encounter 40000 tons per year of extraterrestrial matter and demands that I prove that none of that contains living matter that survives to colonise this planet. Well, he wins hands down on that one. As I have already hinted, proving negatives is no ambition of mine. I do not even undertake to disprove Panspermia in some of its manifestations. I may find the case unpersuasive and emphatically non-cogent, but that is not the same as disproving it. But how persuasive is this shotgun argument? Is all 4e4 tons supposed to be living material? No? Well, then, how much of it is? 1%? 1ppm? 1ppb? 1 microbe per year? 1 nucleic acid molecule per year? Are we to assume that stratospheric bacteria stem from this influx?
These questions are not completely rhetorical, however uncomfortable they may appear to the run-of-the-mill biologist. If there are no living components to the influx, it hardly matters whether the right figure is 4000 tons per year or 4000000 tons per year. If there are any passengers, then it matters a great deal whether they are calculated to survive the journey, the landing, the environment and the reception on arrival. To assume a priori that because we are fielding tons of matter, therefore some of it must be viably importing living organisms, is a bit of a logical leap of faith.
I have furthermore been exhorted not to assume that the exponential function of microbial life lacks the mathematical potential to overwhelm the cubic function of space, because the exponential potential of life will always have pure mathematics on its side in this battle.
Naïve appeals to "logic" or "mathematics" are always rather pathetic. They are the basis of a lot of the mockery to which the "intelligentsia" are held by the man on the Clapham omnibus, and that sort of "intelligentsia" certainly ask for everything they get. Unfortunately the mockery slops over onto serious workers, sometimes quite harmfully. The irrelevance of this particular mathematical claim is worthy of any innumerate politician. In science we never are dealing here with "pure" mathematics. We are dealing with finite time, finite space, finite resources. And one example of the relevance of such finity is that we do not necessarily find that polynomial growth is overwhelmed by exponential growth. The race simply does not necessarily run long enough for a growth factor of say, 1.0001 per generation to overtake say, a cubic function, especially if the generation time is slow. Nor may we assume that an exponential tendency implies effectively exponential growth: "Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it."
For instance, I was challenged with a guestimate of 5e30 microbes living on Earth today, and invited to spread just that life evenly through the galaxy, and calculate the odds that the Earth wouldn't encounter a single cell in 500 millions years. Persuasive, yes? About as persuasive as the physicist's proverbial: "Assume a spherical cow..." Just how is this even spreading to occur, even if we were indeed to assume that the spread bugs would on average survive in space long enough for radiation to kill them. Quite a problem that is, and it is not at all an academic problem; it is characteristic of many aspects of ecology and epidemiology. By way of analogy, consider Ebola fever: any single seriously affected patient will harbour many times more live viruses than the human population of Earth, and its exponential growth dwarfs human population growth, so we all are doomed, right? Not quite yet! We might be if the exponentially growing viruses could achieve even distribution, but the known human toll so far is more like hundreds than thousands, and even allowing for mis-reporting, we do far better to take precautions against lightning than against the dangerously contagious Ebola fever.
Earthly ecology is full of similar cases where exponential biotic potential is throttled by logistic obstacles. Interstellar dissemination promises nothing better. Shotgun strategies are common in biology, but they are no substitute for rational argument.
Old Bottles with Unsuspected New Wine
Recent discoveries of hitherto unsuspected life forms and ecological niches are of great interest to biology in general and astrobiology in particular and panspermists have made great play on them. Particular recent examples include: ocean vent flora, deep subterranean microbes, evidence of far wider ranges of bacteria in ambient circumstances, than we had hitherto succeeded in culturing, and stratospheric bacteria.
Then there have been observations of putative micro-fossils in extraterrestrial material. Panspermists have largely tended to react as though they were living. After all, if they are bacterial, they must have been living once, so why quibble? Now, not to take too cheap a shot at what I regard as a lame-duck theory, if they really are fossil bacteria, this is interesting and if they also are of extraterrestrial origin, this is tremendous, but really, we need a lot more material and a lot more convincing material before we need to resort to extraterrestrial explanations.
Saying how exciting it would be if true, is a pretty lukewarm argument as cogency goes.
Arguments from how tough life is and what a wide range of environments it can populate and survive, are largely naïve. Yes, it is true that we have found life in incredible circumstances, but firstly the life forms tend to be specialised, readily forming prey to less spectacularly tough forms in other environments, or even dying as soon as they are transplanted, and secondly, in most cases they have evolved from inhabitants of everyday environments adapting to the extreme conditions. It is quite possible that abiogenesis on Earth originally did occur in some such tough circumstances as ocean vents or deep earth, but it seems most unlikely that we stem from life that originated equally in all of them!
As for stratospheric microbes, I find the current reports even less persuasive than the meteoritic "fossils". Everywhere we look we find microbes. Sometimes it is contamination. That doesnt prove that it is all contamination, but it does mean that we do not swallow every new report unverified. Other examples reveal channels of infection hitherto unsuspected. For instance, how well is stratospheric air isolated from tropospheric air? Well enough for us to prefer the explanation of exotic to indigenous microbes? That is pretty god isolation! Then again, suppose we assume that our stratospheric microbes are scattered there by comets; how does it come that they are particularly well adapted to that environment? Is their density low enough to be consistent with the observed transparency of space and the suspected rate of seeding from passing comets? Not too long ago we had the fuss about the rate at which cometary aqueous bodies were supposed to be impacting our atmosphere. Has that made much of a lasting impression? It strikes me as a far more modest proposal than invoking comets to explain high altitude bacteria.
Funnily enough, I have not yet seen any support for Panspermia based on recent suggestions that we have identified and succeeded in culturing at most a fraction of a percent of extant microbes. The basis of this claim was investigation of all the DNA to be found in environmental samples and known sources accounted for very little of it. I found it rather persuasive. Surely the panspermists could make a case for all that stuff being exotic DNA that never got established on the planet?
Or maybe I should just learn to shut up instead of fuelling their ideas!
There are a lot of questions to answer more seriously than just by leaping onto every new observation as vindicating Panspermia and uniting the incoherent collection into one great cacophonic substitute for an argument. In fact, I think that this might be one of the great distinctions between the astrobiologists and the panspermists.
Kinky Sex Won't Cut It
But all that was the good news.
Suppose that there really is a lot of organic stuff out there, a continuous, promiscuous, Jovian golden shower of nucleic acids. Suppose that it all comes with the necessary equipment to penetrate and invade target genomes and inseminate them with the blessings of carefully scheduled alien updates. Then how does invading genetic material know which genome to update? Does it avoid the tapir when it is carrying updates for the toucan? Or is that in fact how the tapir got its proboscis? How lucky then, that it wasn't a gene for wings! How does it know where in the genome to splice itself? How does it know which passenger genes to bring along when the novel function requires integrated gene action and wrong placing could cause cancer or instant loss of function? Not many genes for non-trivial functions are viable in the wrong contexts. How does it manage to find its way to the gonads instead of sterilely modifying genomes in somatic cells?
If the answers to these questions are not forthcoming, then we have an embarrassment. You see, if all our planet's major evolutionary advances, or even a major proportion of them, are random and must come from steady state life in a steady state universe, then it would take vast numbers of contributions to explain the key evolutionary events. Even if the imported material were somehow sifted to contain only meaningful genes, none of us would have an unraped gene in our bodies. All our "junk DNA" would be a drop in the bucket. In short, organised life on Earth would be impossible, every genome being destroyed by this continual assault of inappropriate updates.
Then again, what genes are floating round out there? Genes for ultra violet vision for humans? For wings for aardvarks? For human-level intelligence for bees? Or indeed, for bird wings for birds, human intelligence for humans, or ultra violet vision for bees? Or did the supply of these three suddenly dry up once they had achieved their goal? Otherwise why don't lizards get some of the same genes for flying, thinking and so on?
Genes from outer space I might just about swallow, (in fact I already must have swallowed myriads of them, if that thesis is correct) but intelligent, teleological genes, docking with the right genomes according to a logical program, and leaving the rest unharmed? My throat sticks at that; I obviously lack a vital gene for gullibility!
Organic matter from space is another theme that leaves me greatly nonplussed. Every time anyone comes up with more evidence for organic compounds in space, someone is sure to explain how this means that it is possible that life on earth was initiated by those amino acids and the like filtering down in the remote past. Some even speak of such contributions as a necessary source of carbon for the origin of life on the planet! What possesses people to propound anything so vapid? What makes a few kilos of amino acids from space so much more significant than a few billion tons in the oceans and the atmosphere? Has anyone bothered to calculate how much carbon there already was in the earth's crust by the time the process of planetary accretion had approached completion? Something like ten to the fourteen or fifteen tonnes in the top km, I reckon!
Do me a favour! Carbon is one of the commonest elements in the universe and a lot of it accreted into the planet as it formed, and underwent a huge range of chemical reactions under a huge range of local conditions. There is no need to regard subsequent dribbles of possibly a few tonnes or a few thousand tonnes per year as particularly significant.
Recent remarks from the front lines.
Some more correspondence I have had, justifies recognition in this essay.
Proof by Assertion
For one thing I have encountered a fair amount of proof by assertion and reproof by re-assertion, favourite weapons of fringe polemicists. Please note that I do not classify everyone with an interest in panspermists as a fringe polemicist and I do not deny that meaningful research into various aspects of Panspermia is possible, but a goodly proportion of the arguments I see are of the general tone of: "...absolutely ZERO scientific evidence for indigenous abiogenesis and a veritable mountain of negative evidence. Please inform me of the scientific basis for your belief that all Earthly life originated on Earth..."
Such a "mountain of negative evidence" of course, never emerges in the correspondence.
Firstly, there is plenty of evidence supporting either side of the debate. Such claims that there is no evidence, confuse evidence with at least cogent argument, or more typically with proof, of which there is none and not likely to be any in the foreseeable future. Science of course, by its very nature, does not as a rule deal in "proof" in the strictly formal sense, but in the relative merits and weaknesses of rival hypotheses.
Apart from a feeling of helplessness at the prospect of having to explain the concept and function of scientific evidence to persons capable of such assertions, there is the begged question of my "belief" in an assertion that requires proof of a negative, namely that no form of oligospermia ever occurred in our biosphere. Am I alone in taking offence at polemicists who invent my views for me and then demand that I defend them?
Occam in a Subterranean Spin
Another approach is rather engaging in its artless faith in the power of inverted accusation. Occam's razor is invoked on the side of the panspermists! Occam's Razor, I am assured, does not say, "Things are more likely to originate where they are found today." And yet I am told explicitly, this is the nearest thing to evidence supporting belief in indigenous abiogenesis.
That second statement is of course balderdash; I have never heard anyone citing anything like that as evidence. Can you imagine: "My dear Featherstonehaugh, it is obvious that life originated here because not only does the bible say it did, but here we are "
Naaahhh... Not reeeally...
For what it is worth, one certainly can invoke Occam to support the claim that in the absence of contrary evidence, things are more likely to have originated near where they are found today. In fact I cannot imagine what could move one to think otherwise. It seems to me extravagantly eccentric to suggest that from the fact that I find a stone in South Africa, I am to conclude that Occam reckons that it therefore more likely originated in Seattle or Liverpool. That there might be all sorts of other reasons to deduce that it originated elsewhere is another matter, but then Occam demands those reasons before one can claim not to have multiplied entities in reckoning that things are likelier to originate other than where you find them.
Can you imagine: "My dear Featherstonehaugh, it is obvious that life originated elsewhere because not only does Sir Fred say it did, but here we are "
Naaahhh... Not reeeally...
Anyway, no one in his right mind claims that Occams amputator provides proof. It is merely a valuable tool in prioritising our preferences for rival hypotheses. But such as it is, the principle, be it never so weakly, opposes the charming trenchancy of the foregoing denial!
Betting on probability
A slightly more interesting assertion invokes probability theory. We balance the plausibility of two competing assumptions that I quote very loosely and without ascription:
Since, in the absence of any shred of evidence that life is some sort of chemical imperative on Earth, we have no idea how life began, the former scenario is by definition, by a factor of at least 4e11 the less likely origin of life.
Yes. Well, I promise you that it was not my idea and that I really did receive a statement to that effect in my email.
Oh all right! Let's get on with it.
Scenario 1 happens to correspond roughly to what I accept as a vague but persuasive hypothesis on the origin of life on Earth, but I am uncomfortable with such a neat, confident separation of the competing scenarios. For a start, "the first few hundred million years of Earth's history " puts it a bit self-indulgently. Current dating and description of the earliest putative fossils looks pretty reasonable, but offers no sort of watertight palaeontological received truth on a par with say, the Lake Turkana snails or Foraminiferan series from fossilised sea floor material. To be sure, there is a lot of material of great interest, of a very suggestive nature and of great importance, but it is not all of the same quality and not all of the same plausibility. When a palaeontologist shows me a series of systematically varying material over a wide range of times and plausibly matching ecological conditions, I incline to a more charitable view of his claims than when he shows me a rock out of context and claims that the micron-sized nodules are evidence of bacteria in boiling water over glowing lava a million years after the accretion of the Earth, or in a meteorite apparently from Mars or Luna.
Again to be sure, my charity is no proof of correctness nor even of soundness, and apparent fossils in meteorites or in remnants of rock from the accretion phase of the planet may indeed reflect the facts of the matter, but the principle of extraordinary claims demanding extraordinary support is as incisive as Occams razor. It could even be argued to be derived from it, sorta-kinda. That principle, which I have seen attributed to Sagan, is no licence for rejection of sound evidence, and threatens to become a cliché, but that does not imply any weakening of its cogency.
And before anyone hooraws me for such blindly smug uncharity, they should please explain the attraction of any contrary view, such as that the greater the leap of faith demanded, the higher the believability of the claim.
Next, it is far too optimistic to hope to compel my assent by skating hastily over say: "we have no idea how life began". Really? Ever since Darwins "warm little pond" we have had some very persuasive ideas on the subject, so much so that via Urey, Oparin and other, more recent workers, we even have had some very specific criticisms among rival theories. As our familiarity with the mechanisms of life deepens, our views adapt, but really, the gross picture has altered surprisingly little in the last century and a half or so. Details have emerged yes, even vitally important details, such as in the emergence of molecular biology, but who ever expected anything else? We know a fair amount of the relevant chemistry and information theory and for that matter of the physics. We know that it is extremely difficult to construct a plausible scenario for the emergence of life in space, in excessive heat or cold or radiation or the absence of water. So there is a lot we dont know? What else is new? Try finding a field in which we know everything! For instance, suppose that certain of us are right and the source of our biosphere is indeed exotic, how does that mean that we can talk more sense about it than about indigenous abiogenesis? Such a discovery would raise billions of times as many questions as answers, and hooray!
The immediate problem is not whether we know it all, but whether we know enough to talk sense about it and to construct falsifiable hypotheses that will permit us to broaden our "knowledge". ("Knowledge" after all, is not a very respectable term in the practical philosophy of science!)
And what price "any of hundreds of billions of nearby locations (i.e. in our galaxy, I presume) at any time over that last 8 or so billions of years."? It is not clear where the latter figure comes from. Presumably putative ages of the universe or the galaxy. If so, there are plenty of opposing guestimates ranging up to more like 30e9Y. Perhaps the idea is that there are 13e9Y in which everything happened and that in the first 8e9Y life was evolving and boarding the interstellar express for planet-to-be Earth.
The computation of the ratio of probabilities as being 4e11 is commendable as really creative probability theory, but if a student of mine came up with anything of the type, Id have his hide for wiping blackboards! Charitably assuming that 4e11 is the estimate for the number of stars in our galaxy, to imply that our origin from each of our galactic companions is equally likely, or that its successful voyage to Terra in the available time has a probability of approximately 1, is far too greedy! Given say, a probability of 1e-6 for abiogenesis in any given place in the galaxy and 1e-6 for the journey (a ridiculously high figure, I guess) and 1e-6 for successfully colonising our planet's primeval soup, that already makes the ratio of 4e-11 look pretty tame! It is exactly this kind of cheerfully incomplete calculation for only part of the story that has left egg on so many panspermic faces in the past. Of course, one might object to my figure of 1e-6 for abiogenesis on any given planet, but if I am being too stringent, then why did we need to invoke exotic abiogenesis in the first place? We could relax our scepticism about our own spontaneous indigenous abiogenesis!
Reasoning with probabilities in the face of our own ignorance, can be a hazardous occupation, as intellectual occupations go!
Fastening seat belts
Then there is the question of transport problems. It seems that we now can neglect that as an obstacle, if I am to go by the assurance of one correspondent: "Would prokaryote spores survive blast off and entry? Recent evidence suggests ABSOLUTELY YES. From Mars to Earth, blast off from Mars plus entry to Earth did not raise the interior temperatures above 35 C."
This is a fine example of the tendency among committed panspermists to leap from theoretical, putative possibilities to "ABSOLUTELY YES". It is so much more fun than fine distinction between "would" and "could" or even "might". We do not ask whether bacteria in the ablated material would survive, even though the question is important. To assume that they do, is to stretch the implications of the research findings unwarrantably. To accept that only germs inside the modestly warm core of the meteorite survive, means arguing for the occasional germ in the occasional rock to get out whole. How often need we expect that? Once in a geological epoch?
That celebrated evidence certainly is recent, but it is by no means unassailable. Recency is no unqualified merit in research. It is routine to eat words and adjust of conclusions drawn from recent results. That is no disgrace, but how discovery works, not through polemics. The path of science is paved with the corpses of eventually superseded work. In particular, generalisation from observations on one highly atypical rock that has spent a long time on our planet, may be reasonable, but is not at all compelling before we see a lot more such rocks, and preferably some from space. It would be nice to see a few experiments to determine what does happen to inhabitants of rocks that fall to earth after being launched under heaven knows what accelerations and heating, followed by millions of years of drifting unprotected in cosmic radiation, then hitting the atmosphere at say, 20 to 220 km/s.
Of course, testing the millions of years of delay might be challenging, but we could do some innocent extrapolation. The other factors show more promise for investigation. Subjecting rocks to the insults of simulated interplanetary launching and landing should be experimentally challenging, but not really forbidding. Capturing a few representative space wanderers for investigation will surely be just a matter of time.
As for extraterrestrial fossils, we are having enough difficulty distinguishing confusing signals from comparatively recent fossils and even putative living organisms! When we can inspect a category of microfossils in their teeming millions in richly varied contexts we can draw some fairly confident conclusions, but poor material in speculative circumstances demand that isolated observations need to be regarded with deep reserve, rather than at once assuming that suggestive nodules imply microbes on the moon and Mars.
Furthermore, even if the comfortable interior of that rock was in fact a correct inference, it does not follow that this will hold for all sizes of rock. Fine dust will be all right, pebbles will burn up, modest rocks, we are assured, will land their cores coolly and gently. What about really large, fast rocks, whose physical strength we may neglect when they reach the planet? It is hard to imagine their interiors remaining benign.
However, that leaves us with a wide range of small particles and modest-sized rocks that could land microbes safely, doesnt it? Maybe. Ah hae ma doots, but just maybe. But then, that size of rock is not a very encouraging time capsule for keeping nucleic acids safe from radiation, is it?
The same correspondent continues in a similar vein with: "Would prokaryote spores survive journeys of millions or even billions of years? How about 250 million? All evidence here so far points to an answer of ABSOLUTELY YES."
They may be persuasive in headlines, but an important principle in science is that CAPS WON"T CUT IT. "POSSIBLY YES" I might swallow, but not "ABSOLUTELY YES"! In fact where incredible bacterial longevity has been observed so far, it has been in mineral deposits underground, and not all kinds of mineral deposits at that. We have no space-based observations of anything like 25e7Y or even 1e6Y. There is a lot of hard radiation out there and molecular biologists would no doubt love to know some half-lives for frozen spores. For instance, how many of those putative Mars bacteria were alive after their mild launching, riding and landing? Or are we to assume that they were mineralised on Earth while still alive? It is not much good voyaging a space-going Mayflower for aeons, only to fossilise on Earth, is it?
Another assurance is that I am hopelessly conservative about speeds in outer space. I am solemnly rebuked for not realising that the solar system itself is moving at 220 km/s. I am not informed relative to what, or what this has to do with the typical drift speeds of incoming bodies. Nor does it seem to matter with what velocity they strike the atmosphere; presumably rocks that keep their cool and cushion their passengers at 22 km/s will do the same at 220 km/s!
Rising from brass tacks
No, unchastened by recent reports and correspondence, I ungenerously and unregenerately repeat, Panspermia has a great deal of development to do before it metamorphoses into an interesting subject as astrobiology. I may have said this before; I shall certainly say it again: certain subjects, such as probability theory, are easy in principle, but bristle with traps for the unwary. Such subjects include probability and evolution, and their treachery extends to permeate the rest of biology, if any. Panspermists have not come to terms with either, and neglect of homework does not make much of a splash in biology; more of a dull plop.
And bad science does not even make good science fiction unless the writer is a genius.
Appendix: Critical Conditions for Progressive Enlightenment
Anonymous Equine Admonition
On hearing hoofbeats, hypothesise HORSES before thinking of ZEBRAS.
Richfield's Zebraic Addendum:
none the less remains prudent to consider ZEBRAS before diagnosing UNICORNS.
Policy of Rhinal Obduracy.
Principle of capitulatory nomenclature.
Accept it with grace and without hesitation, but also without prejudice to possible future falsification of the conclusion.
Ligneous Cautionary Codicil:
CCCMENU CCC for 2000
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