I continue to be intrigued by the ubiquity of evolutionary stasis as described by Donald Prothero, for example in this piece. It is the breadth and depth of his evidence that makes his case so striking, but the strapline would be:
In four of the biggest climatic-vegetational events of the last 50 million years, the mammals and birds show no noticeable change in response to changing climates.
It’s vanishingly hard to find any species, amongst hundreds, that can be shown to have evolved in response to major climate change. That is a remarkable fact. Instead, he says, the large fauna migrate to stay in their ecological comfort-zone, or go extinct when they can’t. This stasis on a grand scale raises all kinds of issues, but no good explanations (according to Prothero). However, Prothero does point to the paper that really raised stasis as the “dirty secret” of palaeontology, as well as introducing the theory of punctuated equilbria to the world. This 1972 paper by Niles Eldredge (celebrated collector of trumpets) and Stephen Jay Gould (singer in the Boston Cecilia and writer on baseball) – they both did some palaeontology too – Punctuated Equilibria: an alternative to phyletic gradualism, is where I want to direct our attention today.
As Prothero says, this paper is a masterpiece of scientific thought, not least because it takes its philosophical presuppositions, and those of its rivals, seriously. It is sobering to think how palaeontologists, taught the Darwinian theory of phyletic gradualism, managed to impose that interpretation on the fossil evidence they uncovered for over a century, when by far the commonest pattern actually observed was stasis and saltation. Such is the power of theory.
The authors demonstrate the weakness of the relatively few test-cases of gradualism. The paper specifically cites the horse (“a luxuriant branching bush, not the ladder to one toe and big teeth that earlier authors envisioned” – Simpson, 1951); the sea-urchin Micraster senonensis (“a migrant from elsewhere… did not arise gradually from M cortestudinarium” – Nichols, 1959), and the Jurassic oyster (“the transition from Liostrea to Gryphaea was abrupt and neither genus shows any progressive change through the basal Liassic zones” – Hallam, 1959 – he says this finding matches the experience of most invertebrate palaeontologists).
By 1972, biologists had proposed for decades that the commonest mode of macroevolution was allopatric, that is a genetically-mediated speciation arising from the isolation of a small population with an atypical gene pool in a marginal evironment, providing new selective pressures. Our authors’ main contribution was to apply this existing theory to the fossil record and conclude that stasis and saltation was a real phenomenon, and why. Most evolution, they said, occurs in small, out-of-the-way corners, and on very short time scales. Although the resolution of the fossil record means speciation could take a million years and still be unobserved, they maintain that in theory most evolution will take place soon after the population is isolated, in the biological blink of an eye.
The first remarkable thing is that, although some form of allopatric speciation still seems to be the most favoured theory of speciation, gradualism is still maintained vehemently by biologists commenting on blogs like this, in popular science and in textbooks. That “ladder” of horses, for example, is still touted as a textbook example of gradualism, though Simpson debunked it before I was even born. Why is the public message so slow to respond to newer science?
Maybe the answer lies in the authors’ informed and astute observations on philosophy of science. Against so many scientistic writers of our day, they insist that theory always determines data (and remember they said this in a seminal paper a couple of generations ago: it’s scarcely novel or obscure). They cite Feyerabend’s work of just a couple of years before. They affirm Kuhn’s observation that textbooks indoctrinate each new generation of scientists in the theoretical structures that will largely determine how they view the world and its data, and specifically suggest that this is why phyletic gradualism had coloured the interpretation of the fossil record since Darwin. Indeed, they even include a telling 1861 quote from Darwin himself, showing how it undermines his later autobiographical claim to have been led only by the evidence, without imposing any theory:
About thirty years ago there was much talk that geologists ought only to observe and not theorize; and I well remember someone saying that at this rate a man might as well go into a gravel-pit and count the pebbles and describe the colours. How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service.
In winsome frankness the authors concede that the same “theory leading evidence” is true for them: as palaeontologists they have adopted the theory of phyletic gradualism, a mental construct just as Darwin’s gradualism was, because it is the current wisdom of biologists (an argument mainly from specialist authority). And they have used it as a grid on which to map the fossil evidence. Their contention is simply that their theory fits this evidence better, which is actually what good science should attempt:
The idea of punctuated equilibria is just as much a preconceived picture as that of phyletic gradualism. We readily admit our bias towards it and urge readers… to remember that our interpretations are as coloured by our preconceptions as are the claims of the champions of phyletic gradualism by theirs. We merely reiterate: (1) that one must have some picture of speciation in mind, (2) that the data of palaeontology cannot decide which picture is more adequate, and (3) that the picture of punctuated equilibria is more in accord with the process of speciation as understood by modern evolutionists.
Now, following their urging, at this point let us note the logical order here: (1) You’ve got to have some theory, (2) The fossil record doesn’t provide strong enough evidence to settle things and (3) punk eek doesn’t clash with palaeontology and fits better with the contemporary theoretical conjectures about speciation. Their theory, then, is in the end exactly as strong as the theory of allopatric speciation.
Gould’s own examples present a reasonable case for the fact of allopatric speciation – but they primarily support the case that a particular set of changes was fixed by speciation in an unusual location in “one go”, as it were. The actual evidence for the changes in Gould’s example being adaptive isn’t strong at all.
(Incidentally I recognise in this whole discussion that punk eek doesn’t invoke “hopeful monster” saltation – but nevertheless it radically compresses the concept of “gradualism” to below the resolution of paleontology. It is the underlying biological theory – allopatric speciation – that conceives gradualism where, in fact, the fossil record cannot reveal it.)
So what is the positive evidence for allopatric speciation, since Eldredge and Gould adopted it mainly as the frontrunner in current biological theory over other mechanisms like sympatric speciation?
It would appear from review articles such as that in Wikipedia that the evidence is actually rather thin: in the laboratory, Drosophila selected for particular diets apparently show “the possible first steps” to it by appearing to prefer to mate with their own populations. That’s hardly seems conclusive.
In the field, the articles reference various (mainly) sub-species of creature on different islands of archipelagoes. However, the recent doubts over the true significance of the differences between Darwin’s finches make such evidence inconclusive of one particular mechanism.
And another line of inquiry, ring species, is weakened by the gradual removal of examples (eg circumpolar gulls) from the already rather short list, just as in our authors’ own time the short list of examples of phyletic gradualism was being shown one by one to be, in the main, equally well explained by stasis-saltation, though they still populate textbooks today.
But, as they say, “one must have some picture of speciation,” even if it is biased by ones worldview. It’s worth asking what their admitted bias means in practice. At a couple of points in the paper, they reference “creation” in passing. Their worldview bias, unnoticed in the context of a “scientific paper”, appears to blind them to the possibility that they’re actually poisoning the well for alternative (theistic) theories to both phyletic gradualism and allopatric speciation:
Palaeontology supports creationism in continuing comfort, yet the imposition of Darwinism forced a new, and surely more adequate, interpretation upon old facts. Science progresses more by the introduction of new world views or “pictures” than by the steady accumulation of information.
“Surely more adequate” we’ll return to shortly. Note, though that they tacitly admit that it is their metaphysical world view, not any evidence, that alone justifies that word “surely”. Then, in discussing the unwillingness of some previous researchers to admit that humans arose from more “brutish” ancestors, they write:
Hominid catastrophism, according to Brace, is the denial of ancestral-descendant relationships among fossils, with the invocation of extinction and subsequent migrations of new populations that arose by successive creation. Such views are, of course, absurd…
They’re “absurd”, note, even though “the fossil record supports creationism in continuing comfort”. The adverbial phrase “of course” saves having to pinpoint exactly where such creationist views break down. Being interpreted, it all adds up to “we prefer not to go there.”
I guess the “world view” issue in question is the usual naturalistic one: to consider creation as an option, apart from invoking the God that Marxists like Gould wish to avoid, is to take events from the realm of explanation to the impenetrable “God did it.”
But how, in fact, does punctuated equilibria theory give us a better “explanation” in more than theoretical terms? For the suggestion, remember, is that a small sub-population of a species, that we can’t see, retreats to a small isolated environment, that we can neither detect nor, therefore, describe. Over a relatively short time a whole raft of changes occurs, invisible to the fossil record, which produce through adaptive selection (or perhaps, to incorporate today’s leading theoretical model, through neutral change) an entirely new species, which then appears fully-orbed into the light and stays substantially the same until its extinction. Note what they say about “species”:
The coherence of a species, therefore, is not maintained by interaction among its members (gene flow). It emerges rather, as an historic consequence of the species’ origin as a peripherally isolated population that acquired its own powerful homeostatic system.
In other words one real and stable species (or Aristotelian substantial form) invisibly gives rise to a different real and stable species (form).
Let’s apply this to human history, since this is one of their examples. They describe four distinct lineages: Australopithecus, Pithecanthropus (now renamed Homo erectus), Homo neanderthalis and Homo sapiens. Forty three years later that picture is pretty much the same, with other proposed taxa being in considerable doubt and even Neanderthal being shown to have interbred with us.
Yet there is still an enormous investment in filling in the gaps, in order to “explain” human evolution. But the very desire to bridge such gaps presupposes phyletic gradualism, which has been in disgrace since long before even Eldredge and Gould.
If punctuated equilibria theory is true, then it would predict that there aren’t any significant gaps in the fossil record, or at least any that we’re remotely likely to find, since none have ever been found in the entire fossil record. A small population of Australopithecines disappeared into its dark evolutionary burrow, and reappeared in the spring transformed into Peking man. Later, in another dark corner, a few of the latter disappeared to emerge as people just like us, at least as far as biology is concerned.
We ought not to find much more evidence. We can’t know anything about the environmental conditions in these dark corners, nor therefore give any adaptive explanations for mankind that aren’t pure myth-making – if, indeed, adaptation had a part to play rather than just neutral drift, which is a non-explanation.
So in fact, under punctuated equilibria we’re left with no more complete an explanation than the one our authors reject on ideological grounds – direct creation by God. To me allopatric evolution and direct creation appear to have about the same explanatory power in any particular instance, except that the latter provides a potential meaning to the emergence of man, where allopatric speciation can only shrug its shoulders and say “stuff happens”.
I’m not suggesting that this means that creation, sans mechanism, is the preferred explanation for speciation, including our own rather special case. For any such preference either depends on scientific evidence – which according to Eldredge and Gould is unlikely to be forthcoming – or on worldview – which arises from the kind of evidence in which science doesn’t, or at least shouldn’t, deal.