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Thursday, April 10, 2008

The many meanings of "evolution" - no wonder we get confused!

One thing that confuses people who are trying to follow the intelligent design controversy is that the word "evolution" is used by different people to mean strikingly different things. Embryologist Jonathan Wells notes,

"Evolution" has many meanings. It can mean simply "change over time." The present is different from the past. The cosmos evolves. Technology evolves. No sane person denies evolution in this sense.

In biology, "evolution" can also refer to minor changes within existing species. Nobody denies evolution in this sense, either. People were observing such changes for centuries before Darwin came long; they were even producing them in plants and animals by artificial selection. Darwin (and Wallace) pointed out that something analogous to artificial selection operates in natural populations, but there is nothing "Darwinian" about artificial selection.


also
Lest some people mistakenly conclude that I accept Darwinian evolution broadly defined, I will make two other distinctions. The first is between "microevolution" and "macroevolution," and the second is between "macroevolution" and "Darwinism."

Regarding the first: Almost eighty years after Darwin published The Origin of Species, neo-Darwinist Theodosius Dobzhansky noted that there was still no hard evidence to connect small-scale changes within existing species (which he called "microevolution") to the origin of new species, organs and body plans (which he called "macroevolution"). Dobzhansky wrote: "We are compelled at the present level of knowledge reluctantly to put a sign of equality between the mechanisms of macro- and microevolution, and proceeding on this assumption, to push our
investigations as far ahead as this working hypothesis will permit."

1. Unfortunately for Darwin, there has never been a confirmed case of natural selection producing a new species, much less new organs or body plans

2. So in 2008, seventy years after Dobzhansky and a century and a half after Darwin, the extrapolation from microevolution to macroevolution is still just an assumption.


Concerning the second and final distinction: Darwin didn't just claim that natural selection could produce new species, organs and body plans. He went much further and argued that (a) all species are biologically descended from a common ancestor, and (b) their features were produced entirely by unguided natural processes. He wrote: "There seems to be no more design in the variability of organic beings, and in the action of natural selection, than in the course which the winds blow."

3 It is the claim of universal common ancestry coupled with the exclusion of design that I call "Darwinism."

So "Darwinian evolution" can mean changes in existing species ("microevolution") due to natural selection. This is what Egnor referred to as "obviously true," and I agree. But for some people "Darwinian evolution" also includes the extrapolation from microevolution to macroevolution. This is far from obviously true; indeed, the evidence for it is underwhelming, at best.

Actually, natural selection tends to conserve, not create.

See, for example, Thoroughbred by Design? Mustang by Chance?

and

Natural Selection: Tracking the Primitive Dog

to see how natural selection works in horses and dogs.

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