The myth of common descent

Denyse O’Leary says something on Best Schools  that I too have been intrigued by for some time. Many (though not all) biologists hold to “universal descent from a single cell” as a dogma central to evolutionary theory.

That’s odd, because historically even Darwin, at the dawn of knowledge about early life, spoke of life “breathed into a few forms or into one”, really only implying that there has been divergence rather than stasis. Since then, apart from the opinion of those like Carl Woese that the superkingdoms of life represent separate origins, we have a large body of evidence about horizontal gene transfer and symbiotic events at key evolutionary points. Life has been so thoroughly mixed that some refer to a “web of life” and regard Darwin’s “tree” as no longer tenable.

On the face of it, it seems entirely plausible that the complexity of life is easier to explain, in naturalistic terms, by a series of entities each solving part of the survival problem and, early in earth’s history, pooling their resources by whatever series of timely accidents of ingestion or fusion, than by a one-off event or even a linear pre-evolutionary sequence.

To claim a single common ancestor for all life, implying that life could only arise once in the entire history of the world, is to declare that it was supremely fortuitous. Pursuing origin of life studies is therefore a waste of effort in principle, for if there are natural processes tendng towards life, which can be studied and maybe reproduced, then it would have happened more than once. if the event was so improbable as to be unique, it happened despite natural processes, rather than because of them. Origin of life research is then as futile as scientific study of the resurrection.

Similarly the search for life on Mars is, accepting the principle of universal common ancestry, irrational: an event that could only have happened once in the fertile conditions of earth is vanishingly unlikely to have happened again on a smaller, colder and drier world. Universal common ancestry makes life likely to be a rare commodity in the cosmos: conversely, belief that life exists everywhere tends to suggest multiple origin events here on earth.

You’d think that the natural preference of the scientific community would be for an explanation consistent with the principle of uniformity. You’d expect them to say that life happened because, although we don’t know the mechanisms yet, conditions in the beginning were so conducive that it was cropping up all over the place. That would in no way deny the likelihood both of extinction of the less competitive types, and the homogenisation of life-forms over the billennia so that they all share the same fundamental characteristics today. If life really is “bound” to arise, then it’s probably going to happen consistently enough for different lines to share sufficient chemistry to swap it around in some manner. That may sound vague, but vagueness seems to be the norm in OOL.

Instead, common ancestry is held an article of faith, and expressing doubts about it raises a more-than-scientific opprobium. “Faith” is the operative word here, for there’s a mythic quality to the idea of universal common ancestry no less attractive than the idea of Adam and Eve as the first human pair – and on considerably less evidence if one allows for the range of possible explanations  for their headship of humanity. There are certainly more implications for theology in denying Adam and Eve’s historicity than there are for evolutionary theory in doubting common ancestry. At worst one must posit a greater contribution for horizontal mechanisms like gene transfer (which are known to have happened  anyway) and at best one becomes more optimistic that a reproducible explanation for life might be found. At least by an order of magnitude or so, and every little helps.

But maybe the compelling power of myth goes beyond the requirements of science. Or maybe there’s an unconscious intuition that life really is a miracle.

Jon Garvey

About Jon Garvey

Training in medicine (which was my career), social psychology and theology. Interests in most things, but especially the science-faith interface. The rest of my time, though, is spent writing, playing and recording music.
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8 Responses to The myth of common descent

  1. GD GD says:

    Jon,

    This may be slightly of-topic, but you have talked of teleology a few times; the PoS by Rosenberg (I mentioned this previously) has some interesting comments on why science does not worry about teleology, but the social sciences need to, even those that assume an evolutionary outlook. I mentioned before that Darwin presented a semantic theory –such an approach defies ‘definition’ as understood by science, but it also ‘naturally’ leads to a number of models, some of which may apply to some cases, and may not to others. This is one of the reasons why serious biologist who subscribe to Darwin try to avoid discussing laws or regularities that science observes in all other areas. The discussion is lengthy and there is no way to prove or disprove anything in such a case – that is why I consider this area more one of belief and preference, rather than a ‘brute fact’ of science – such a view is simply not accepted by any serious thinker. Rosenberg also shows that one of the great appeals to Darwin was the removal of teleology in nature; otherwise we are left with Aristotle’s prime mover, or the Christian view that ‘in the beginning God created the heavens and the earth’.

  2. Jon Garvey Jon Garvey says:

    I’ll have to read Rosenberg at some stage, GD. Isn’t it fascinating that Asa Gray thanked Darwin for restoring teleology to biology, to which Darwin responded with appreciation.

    It seems to me, though, that he was either being disingenuous, or didn ‘t realise the implications of his own theory, which as you say was its great appeal not so much, at the time, to fellow-scientists as to the skeptical lay intelligentsia of the time.

  3. James says:

    Jon, Darwin’s reply to Gray on that point has always puzzled me, because in an equally famous comment on Gray (whether it was in a letter to Gray or in another writing, I can’t remember), Darwin rejects Gray’s notion that evolution “was led along beneficial lines” — which would appear to be a rejection of teleology. It may have been in that comment that he said he saw no more direction in evolution than in “the direction in which the wind blows.”

    It is possible that Darwin changed his mind between the two different reactions to Gray; it is possible that he was being less than honest with Gray in the one favoring teleology (after all, Gray was promoting Darwin’s work among Christian scientists, and it wouldn’t do to dampen his enthusiasm); it is also possible that Darwin understood Gray’s two statements differently, and therefore could agree with one and disagree with the other.

    In the last case, Darwin would have believed that evolution could be teleological in one sense, but not in another — not in the sense of guided or led to particular outcomes by particular interventions. This would perhaps suggest that Darwin anticipated the vague solution of modern TEs, that God “creates through randomness” or that God’s control over a free nature is a “mystery” but nonetheless real. But if Darwin held any such proto-TE view, he was remarkably silent about it. Other than that one remark to Gray, I don’t know of anything he said in his entire published corpus, or in his private correspondence, that would suggest that he believed in or even had much intellectual respect for any version of theistic evolution. And no biographer of Darwin known to me has uncovered any enthusiasm for TE in the recorded remarks about Darwin by people who knew Darwin personally or corresponded with him, beyond that one remark to Gray. So if Darwin was an early TE he was the most anemic and toothless TE on record. And his candid autobiography appears to rule out such a possibility *a priori*.

  4. Jon Garvey Jon Garvey says:

    Yup – agree with that assessment, James. It would appear that Darwin scholars disagree about whether Darwin lurched about in angst-ridden uncertainty about divine influence, or whether his writings lurched around to make the right impression on his readers, whist he privately rejected it all.

    Small matter – I don’t think anyone sees much trace of any providential planning in his ideas… he started as a Deist, after all, and was hardly likely to have move towards true theism, given all we know of him.

    However it does seem to me that like everyone of the time he instinctively thought in terms of progress and perfection. To that extent NS was theory of creation, with European man as its pinnacle. I don’t think the concept of man as a plague on nature, or bacteria as the most successful outcome, would have had any traction at all in Victorian times.

  5. James says:

    Thanks, Jon.

    Your claim that Darwin started out as a Deist — it could be challenged. If we take his own words as entirely honest, he accepted a fairly literal reading of the Bible when he set out on the Beagle voyage. Of course, you could respond that Darwin’s autobiographical statements about his religious life must all be taken with a grain of salt. I’d agree. Nonetheless, a Darwin scholar would ask you to document the claim of Deism. Do we have other statements of his that indicate an early Deist position? Or are you inferring it from the fact that he came from a family of liberals and freethinkers?

    As for progress, I think that as a Victorian he probably did think in those terms regarding social and political matters. However, I didn’t notice in the *Origin* any claim that evolutionary change was intrinsically progressive. It seems to me that he indicates that there can be loss as well as gain of functions and organs – simplification as well as complexification — and that there can be long periods — hundreds of millions of years, even — where some species stay the same because they are suited to their environment. I grant that he may frequently speak of higher levels of organization, higher faculties, higher animals, etc., but I see those as technical descriptions, and I don’t get the impression that he thinks evolution inevitably tends to produce any particular thing, not even man. But if I’ve missed some statements, by all means, let me know about them — I make no claim to complete understanding of any of Darwin’s works or his thought overall.

    Certainly I agree with you that Darwin wouldn’t have endorsed the “man is a plague on nature” view; but I see his position as, not the reverse of that (man is the pinnacle of nature), but as “man is a product of nature like everything else.” That doesn’t mean, of course, that Darwin was blind to the features of man that make him more powerful and amazing than other creatures — intelligence, technological capacity, moral virtue, etc. But it means that nature didn’t intend those features of man any more than it intended the features of bacteria. So Darwin’s assertion of the dignity of man — which he has to believe in, as a liberal, progressive Victorian — can’t really be based on his evolutionary theory. The most he can say is that the conditions were right for the emergence of a rational, creative, compassionate being; he then has to derive the moral and social principles that will guide this being from somewhere else.

    So it’s either evolutionary ethics, such as might be derived from the account in The Descent of Man, or the tacit importation of Christian ethics (without the theology that once sustained them). I think in practice he chose the latter route, because Christian belief was still deep in his bones, even though he rejected it consciously. But of course his modern descendants, stripped of that deep belief, follow the lead, not of Darwin the Victorian, but of Darwin the author of The Descent of Man. And they aren’t any more successful in coming up with a *normative* ethics (as opposed to a biological account of the origin of ethics) than Darwin was.

  6. Jon Garvey Jon Garvey says:

    James

    I wouldn’t want to to pontificate where Darwin commentators from Warfield onward disagree. Apart from hearsay, my impression of Darwin’s likely theological mindset comes (a) from his personal background and the tenor of the times for radically-minded scientists, (b) the terms in which the religious arguments in “Origin” are couched and (c) the nature of his disagreements with Fitzroy on the Beagle. But I’m happy to let the historians argue it out.

    The kind of passage that I mean regarding perfcetionism might be like that on the last page of the origin. A few extracts:

    And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection.

    … extinction of less improved forms.”

    Thus… the most exalted object that we are capable of conceiving, namely, the production of the higher animals, directly follows.”

    Given the buiding of his theory on analogy with selective breeding (which early in the book he equates with overall improvement from the breeder’s “instinct” for the best, and not merely specific traits); and given the obsession of nineteenth century writers with bloodlines. racial purity, etc, I defend my claim that he saw evolution as a perfecting mechanism, never really noticing that he failed to define perfection.

    Similarly, in the “Voyage”, his passage on the extinction of races when colonised by whites mentions the devastation caused by our diseases, but refers to a “mysterious agency”, namely that it is the same as with different species of animals – “the stronger always extirpating the weaker.” The thought that mass migration of Africans to Europe might decimate whites with unknown diseases wouldn’t occur to him – the physical, mental and moral superiority of the white race was almost axiomatic for the time. I hope to allude to that in the blog soon.

  7. James says:

    OK, Jon, I now see what you are speaking about.

    I think that statements of the sort you quote are found in the conclusion of the Origin, and are not very common throughout the body of it.

    I wonder about Darwin’s logic. Granted that natural selection will tend to improve forms, that doesn’t automatically lead to “the production of the higher animals.” For example, a destructive species of bacterium might “improve” by developing resistance to all existing antibodies. The “perfect” bacterium would be one that was resistant to all antibodies, not the one that became an antelope. In fact, a bacterium resistant to antibodies would be virtually immortal, through its offspring, whereas of the higher species, supposedly most that have existed have become extinct, showing that they are less fit than simpler creatures — bacteria, molds, insects, etc. which have survived for much greater lengths of time. Evolution doesn’t aim at the “highest” — it aims at that which survives. If what happens to be better at surviving is a simpler, cruder creature, incapable of reason or love or pity, well then, there is no reason the higher animals should “directly follow.”

    Even the animal breeding analogy, if taken strictly, doesn’t help Darwin here. Sheep become better sheep, oxen better oxen, pigeons better pigeons. No one breeds guinea pigs or hamsters or other rodents in hopes of eventually producing one that can think, compose symphonies, or sing songs. (Alvin and the Chipmunks notwithstanding.) Breeders want the most perfect guinea pig, not a species that transcends guinea pigs. If natural selection is like a breeder, it won’t create anything radically new, but will refine what already exists.

    (Of course, Darwin believed that natural selection did more than that, but insofar as it does more than that it goes beyond the function of the breeder.)

    I’d say the same about white men versus Africans etc. Darwin doesn’t appear to be thinking straight. If a solar flare destroyed all electrical circuits on earth, white Europeans and North Americans and Japanese would be helpless and die by the millions, whereas Amazonian headhunters would do quite well by comparison, since they don’t need electricity. And if a new Ice Age occurred, the Eskimos (the ones who haven’t been softened by modern conveniences) would survive better than the Germans or the Americans, even though by Darwin’s standards they are culturally “lower.”

    My quarrel here isn’t with you, Jon. I admit Darwin says what you say. But his assertions seem at odds with each other. If evolution works the way he says it does, I see no guarantee that higher creatures will evolve. It seems that his remarks in his conclusion, and his remarks on primitives, reflect his Victorian culture and his wishful thinking, rather than the logic of his theory.

    It seems to me that Gould’s remark about the utterly unpredictable nature of evolution is truer to Darwin’s premises than Darwin’s “progressive” conclusion in the Origin. It could well be that on most planets, nothing evolves higher than snails or lobsters, maybe even nothing higher than sponges. It might be only on certain very rare planets, under certain very rare conditions even for those planets, that higher life evolves. Not natural selection in itself, but the environment in which natural selection operates, is what decides how much organic diversity there can be, and how useful it will be to develop a complex nervous system, etc. A world in which the only safe place for life was a network of damp underground caves would not develop human beings. Probably it would not develop mammals or even birds. Amphibians might be the highest life-forms. Not likely you’d find a Victorian freethinker on such a world.

    Now if you adopt a different model of evolution, e.g., that of Bergson, then you would indeed expect evolution to be “progressive.” But if Darwin’s process, on a given planet, produces steadily more advanced species, that would appear to be just luck of the draw. It might well be said by Darwin that evolution on earth has been a progress from lower to higher, but I don’t see how he could have predicted that, based on the abstract idea of natural selection alone.

  8. Jon Garvey Jon Garvey says:

    James

    This I think is the fascination of worldviews in historical context. It would have been virtually impossible in the 19thC intellectual climate to think of evolution other than in “improvement” terms, because progress was the whole backdrop of social and political thought (right up until about the 1970s, in my view, when disillusion set in).

    Part of that came from the leftover Christian view that God made a good creation (so the question to answer in denying it is, “How did it get good without God?” rather than thinking to question that it was good). Darwin, I think, asked tentative questions about nature’s cruelty, but saw it as the means by which nature raised itself up. Later cynics denied that it did rise.

    That said, apart from the mindset, the theory as he presented it would, intutively, deliver the most perfect adaptations (but the “progress” mindset could not conceive that this might work against reason, morality etc). But Darwin proposed infinite variability, and a steady environment that would hone them. Stepwise mutations, drift, and neocatastrophism have made life less tidy since (as have the relativisitic developments in social thought).

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