Tuesday, April 26, 2016

Evolutionary Theory vs. The Theory of Evolution

Who or what is driving evolution?
Evangelical atheist Professor Larry Moran writes a very useful blog post here. The title of the post is "Don't call it the theory of evolution". His justification for this title, and I probably agree with him, is that evolution is, in fact, a cluster of ideas and theories about the mechanism of evolution which are better termed "Evolutionary Theory" since there really isn't such a thing as The Theory of Evolution. This is what he says (my emphases):

What do scientists really mean when they refer to "The Theory of Evolution"? There is no single theory of evolution that covers all the mechanisms of evolution. There's the Theory of Natural Selection, and Neutral Theory, and the Theory of Random Genetic Drift, and a lot of theoretical population genetics. Sometimes you can lump them all together by referring to the Modern Synthesis or Neo-Darwinism

Instead of using the phrase "The Theory of Evolution," I think we should be referring to "evolutionary theory," which may come in different flavors. The term "evolutionary theory" encompasses a bunch of different ideas about the mechanisms of evolution and conveys a much more accurate description of the theoretical basis behind evolution. Douglas Futuyma prefers "evolutionary theory" in his textbook 'Evolution' and I think he's right. It allows him to devote individual chapters to "The Theory of Random Genetic Drift" and "The Theory Natural Selection."

Larry goes on to quote Douglas Futuyama (I have the same book, Evolution) who actually gives a very general definition of evolution that Larry himself has touted. I emphasize the aspects of this general definition in the bold emphases below: 

So is evolution a fact or a theory? In light of these definitions, evolution is a scientific fact. That is, descent of all species, with modification, from common ancestors is a hypothesis that in the past 150 years or so has been supported by so much evidence, and so successfully resisted all challenges, that it has become a fact. But this history of evolutionary change is explained by evolutionary theory, the body of statements (about mutation, selection, genetic drift, developmental constraints, and so forth) that together account for the various changes that organisms have undergone.

We now know that Darwin's hypothesis of natural selection on hereditary variation was correct, but we also know that there are more causes of evolution than Darwin realized, and that natural selection and hereditary variation themselves are more complex than he imagined. A body of ideas about the causes of evolution, including mutation, recombination, gene flow, isolation, random genetic drift, the many forms of natural selection, and other factors, constitute our current theory of evolution, or "evolutionary theory." Like all theories in science, it is a work in progress, for we do not yet know the causes of all of evolution, or all the biological phenomena that evolutionary biology will have to explain. Indeed, some details may turn out to be wrong. But the main tenets of the theory, as far as it goes, are so well supported that most biologists confidently accept evolutionary theory as the foundation of the science of life.

What we have here is a concept of evolution that can be roughly characterized as mere continuity of change with the full range of proposed mechanisms of change up for grabs. This form of evolution which is accepted as "fact", is so general that it could include all sorts of hidden mechanisms that entail "modification" perhaps even the tinkerings of an intelligent designer! - not that I'm necessarily suggesting that, but just to illustrate the generality of the fact of evolution! This kind of evolution as "fact" is a very broad tent indeed! Larry has posted on this very general definition of evolution before and I did a post on his post here

However, it is quite obvious that Larry and Futuyama wouldn't actually have the mechanism of intelligent modifications in mind; rather they are likely to opt for mechanisms implicit in  the mathematical "law and disorder"* objects of the physical canon. In fact as we read above both Futuyama and Larry seem confident that the main causes of evolution have been nailed. Nevertheless, there is just enough maneuver room here for the homunculus Intelligent Designers!

Here is one of the statements by Larry which I quoted in my original post on this general definition of evolution (My emphases): 

Neil deGrasse Tyson said that the theory of evolution is a fact. This is not correct. Evolution is a fact. Evolutionary theory attempts to explain how evolution occurs. Some of the explanations, like natural selection, are facts but many aspects of modern evolutionary theory are still hotly debated in the scientific community.

And by "evolution" Larry doesn't mean a great deal more than continuity of change. However, I doubt if they will be debating if a homunculus is involved!

Finally in his post Larry concludes with:

When you're talking about the mechanisms of evolution, please use "evolutionary theory" instead of "the theory of evolution."

Will do!

* Or "law and randomness". By this I mean that the calculations of the physical canon use both short time, small space algorithms and the statistics of disorder. See here for more technical details on the meaning of short time, small space algorithms and randomness. The deep question is why should these relatively simple mathematical objects predominate when other possibilities exist?

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