Tuesday, September 06, 2005

is evolution scientific?

Dean has sparked another discussion on evolution vs. intelligent design. Nothing brings in the commenters like evolution. As always, there are people in the discussion who think they can wave the question away by claiming that evolution is scientific and the alternative is not.

How can it be that the theory of evolution, by which I mean the theory that all life originated and evolved by purely physical processes, is scientific but the negation of that theory is not scientific? Suppose Fred and Barney find a funny-shaped rock and Fred says that the rock is natural while Barney says that it is man-made. Fred can't just end the argument by saying, "I'm sorry, the theory that the rock is man-made is not falsifiable so that is not a scientific theory."

That is exactly what many people do in response to anyone who rejects the theory of evolution. This amounts to the position that there is an a priori (that is: not empirical) test for certain questions about the world. It rejects a fundamental premise of science: that to answer empirical questions you need to make empirical observations.

Did life evolve by accident or design? According to many people we can answer this question without actually doing any scientific investigation because one answer is scientific, rational, respectable and the other answer is unscientific, irrational, religious. They know this a priori and no further argument is warranted beyond waving their hands and chanting "not falsifiable, not falsifiable".

Does that sound like a scientific position to take?

A commenter with the handle TallDave claims that my "analogy" is flawed because Barney doesn't require divine intervention. As another commenter points out, ID does not require divine intervention either, but that is not really relevant since I wasn't arguing by analogy but by logical form.

This is very common in logic. Suppose Fred tells Barney that he can prove that dinosaurs are birds. He says "All dinosaurs lay eggs, right?" Barney agrees. He says, "All birds lay eggs, right?" Barney agrees. Then Fred concludes "Therefore all dinosaurs are birds."

What Barney can do to refute this reasoning is to come up with another syllogism that has the same form but that Fred agrees is wrong. Barney says "All men are people, right?" Fred agrees. Barney says "All women are people, right?" Fred agrees. Then Barney concludes "Therefore, all men are women."

If Fred sees the flaw in Barney's syllogism then he must agree that his own syllogism was flawed. Alternatively, he can deny that the two syllogism's have the same form, but to do so, he must provide some logical rule for distinguishing the two kinds of syllogism.

TallDave has not done this. Nor has anyone else who claims that they can decide between evolution and design simply on the basis of a priori reasoning. TallDave thinks that he can just say "divine intervention" and that settles it, but divine intervention is not a logical feature, it is a material one. And until someone can give an account of the special faculty by which human beings can know by sheer intuition that divine intervention does not exist, that is not a valid objection to my analysis.

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