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.