Remote, arid, and uninviting, the Galápagos Islands are a curiously inauspicious site for the dawning of an intellectual revolution. However, on his fateful visit in September 1835 aboard the British survey ship HMS Beagle, what Darwin saw on this remote archipelago would be vital to the development of his radical new evolutionary worldview.
Among the most remarkable of all the unique species of the archipelago is a set of 13 closely related types of finch. Their close relationship, confirmed by recent DNA analysis, is indicated by the fact that they all exhibit the same nest architecture, egg coloration, and complex courtship display. However, in other respects, including plumage, behavior, and beak morphology, they are distinct. Each species is peculiarly adapted to a particular ecological niche on one or several of the islands of the archipelago and possessed of a unique beak morphology adapted to a particular type of food — seeds, insects, etc.
Reflecting on this remarkable group of birds, Darwin famously (and rightly) inferred: “Seeing this gradation and diversity of structure in one small, intimately related group of birds one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”1
In other words, species were not specially created. Existing species had descended with modification from pre-existing species. For Darwin, this realization was, as he later described it, “like confessing to murder,” so entrenched was the then universally accepted doctrine of the fixity of species. Darwin also inferred that the major causal mechanism responsible for their adaptive divergence — the shaping of their beaks for example — is the simple mechanism of natural selection. More specifically, the cumulative selection of successive small adaptive changes has fashioned each species step-by-step with a morphology perfectly suited to thriving in “its” special ecological niche.
Darwin also speculated (in Chapter 4 of the Origin) as to how cumulative selection might gradually lead to increasing morphological and behavioral specialization of well-adapted varieties, which over time might lead to the origin of new species.
As far as the evolution of finch beaks is concerned, there is no need either at the morphological or genetic level to call for any causal agency other than cumulative selection.Here I concur with classic Darwinism. The beaks are clearly adaptations and their evolution is entirely explicable within a classic functionalist framework. As the different beak forms are clearly contingent adaptations which evolved to meet the unique environmental demands on a group of volcanic islands that only emerged from the Pacific a few million years ago, their evolution is beyond any structuralist or “laws of form” type of account.
But the highly touted success of Darwinism in explaining the evolutionaryadaptation of the finches is a two-edged sword. While these cases demonstrate that cumulative selection can generate small degrees of adaptive evolutionary change in tiny incremental steps, they also reveal what is necessary for natural selection to explain any change in a species. The lesson of the Galápagos is simply this: Cumulative selection will work its magic as long as the novelty of interest is adaptive and there is a functional continuum (at the morphological or genetic level) leading from a putative ancestor species to a descendant species. The problem, as I show throughout Evolution: Still a Theory in Crisis, is that the origin of the majority of novelties are not approached via functional continuums and cannot be explained in the same way.
Because cumulative selection acts only to adapt an organism to its immediate environmental conditions, without any concern for what the long-term consequences of any specific adaptation might be or where it might lead, it has no foresight. And without foresight, the ends or designs it can achieve are those (to employ Dawkins’s aptly chosen analogy) of a “blind watchmaker.” Each tiny change must be adaptive in order for natural selection to see and keep it. Long-term changes that are only adaptive at the very end cannot be achieved via natural selection.
In many places in the Origin, Darwin conceded that cumulative selection necessitates a long series of adaptive intermediates linking ancestor with descendant. Indeed over and over again he confesses the need for “innumerable transitional forms.”2 Acknowledging “that natural selection generally acts with extreme slowness,”3 he admits that “as natural selection acts slowly by accumulating slight, successive favorable variations, it can produce no great or sudden modifications; it can only act by short and slow steps.”4
Self-evidently, to go from ancestor A to descendant B via cumulative selection does require, as Darwin rightly infers, a long sequence of adaptive transitional forms.
Consequently, Darwin’s interminable series of transitional forms is necessary for straightforward mechanistic reasons (how else can one get from A to B by cumulative selection?), but it is also essential if the sole agency of change is to be natural selection. Where a complex adaptation — no matter how complex — can be reached in a series of tiny adaptive steps, then natural selection can indeed function, in Dawkins’s description, as a blind watchmaker and change A into B without any other causal agency being involved. And it is this elimination of the need for any alternative or additional directive mechanism guiding the evolutionary process that is, for atheists and materialists like Dawkins and Dennett, its great attraction.
If Darwin had gone no further than providing an explanation for the evolution of finch beaks and other cases of microevolution, he might have gone down as a notable Victorian naturalist. But Darwin went much further. He became one of the most influential thinkers in Western intellectual history by making the radical claim that the origin of all the novelties in the history of life, all the taxa-defining traits, all complexity, all biological order, could be explained by extending or extrapolating, over great periods of time, the same simple, undirected, and 100-percent-blind mechanism of cumulative selection that fashioned the different finch beaks on the Galápagos.
The significance of Darwin’s extrapolation can hardly be exaggerated. If it was correct, the problem of evolution would be essentially solved, and the emergence of all species, including mankind, finally explained without any recourse to teleology or design. And for some current hardline Darwinists, the problem of evolution is indeed regarded as solved: New forms of life are the outcome of the machinations of a “blind watchmaker.”
The extrapolation from micro- to macroevolution is certainly seductive. But the fact that an unseeing watchmaker can work his magic on a small scale (as on the Galápagos) does not warrant the assumption that all the order of nature (including all the type-defining novelties) is adaptive and can be assembled via functional continuums. There is an almost universal precedent, as the history of science testifies, that over and over again theories that were once thought to be generally valid have proved eventually to be only valid in a restricted sphere.
I believe this will prove to be the case with Darwin’s mutation-selection mechanism. The need for adaptive continuums brings us to the nub of the problem, and one of the major points defended in Evolution: Still a Theory in Crisis. Practically all the novel, taxa-defining homologs of all the main taxa are not led up to via adaptive continuums. I will argue in later articles that much of the order in nature including many of the taxa-defining novelties appear to be non-adaptive and other features of the biological world that challenge the Darwinian picture of life.
(1) Charles Darwin, Voyage of the Beagle (1845 edition), Chapter 17, 402.
(2) Darwin, Origin of Species, 6th ed. (London: John Murray 1872), 134.
(3) Ibid., 84.
(4) Ibid., 413-414.
Image credit: RuyCalderon (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons.