Tuesday, July 27, 2010

318. Some Thoughts on Evolution, Natural and Cultural: 2

The problem of the "fossil gap" is especially interesting because 1. it did, for a long time, represent a genuine problem, where the evidence, or lack of it, appeared to contradict the theory; 2. natural selection continued, nevertheless, to be accepted by almost all scientists, despite what appeared to be a clear inconsistency. Was there, as Le Fanu suggests, some sort of conspiracy among scientists too arrogant to admit that their "reductive," "materialistic" view of the world could be wrong? Or is there something fundamental about science that Le Fanu has failed to grasp?

As I see it, Le Fanu is clearly out of his depth on this matter. He has presumed science to be something it is not and thus winds up attacking a straw man he himself erected. Natural selection is accepted by most scientists, first because it is the only explanation that's ever been offered for the patterns we find, among both fossils and living creatures, that makes sense; and second, because there is an overwhelming body of evidence that supports it. What Le Fanu refuses to recognize is that, despite the simplicity of Darwin's (and Wallace's) basic insights, the whole field of evolution, now enhanced in so many ways by so many branches of biology, paleontology, geology, genetics, cognitive science, etc., is extraordinarily complex, with a great many very difficult problems still unsolved.

The "fossil gap" is, however, no longer one of them. It is now understood quite well, thanks largely to Ernst Mayr's notion of "allopatric speciation," as expanded into the more general theory of "punctuated equilibrium" by Niles Eldredge and Stephen J. Gould. What Mayr noticed was that, in the great majority of cases, new species develop by "budding" rather than "splitting"; i.e.
a new lineage buds off from the parental one by peripatric speciation [speciation occurring in a peripheral location] and enters a new adaptive zone in which it evolves rapidly, while the parental lineage remains in its old environment and continues at the previous slow rate of change. . . The rapid change of the derived lineage as compared to the slowness of the parental one will undoubtedly be reflected by a gap in the fossil record (What Evolution Is, p. 191).

In other words, while a gradual, step by step process is required by Darwinian evolution, there is no reason to assume (as Darwin himself apparently did), that all such processes must proceed at the same tempo. Punctuated Equilibrium builds on this idea by emphasizing the related notion that once a population is securely established in a stable environmental niche it may remain essentially unchanged for millions of years. When the environment changes, however, or when one branch wanders off into a new environment, the process of natural selection can accelerate rapidly, to produce a new species with very different features during a relatively short period. The intermediary stages required by natural selection are assumed to be there, but since they will have occurred over such a brief period of time, it becomes highly unlikely that any of their fossil remains will ever be found.

Interestingly, Mayr refers to the same process as "bottleneck evolution" (p. 194), which associates the same general principle with the notion of a "population bottleneck" that I've so often referred to on this blog. While evolutionists prefer to think in terms of hundreds of thousands or millions of years, population geneticists have spotted very similar processes at work over much briefer spans, including certain key moments in the "Out of
Africa" migrations.

To be continued . . .

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