I really like Bethell. Why? Because, over and over again, he makes it completely clear how stupid and dishonest the creationist movement is. And the fact that Discovery Institute happily features his blathering can only be good for our side. What could be better than to see creationists discredit themselves so frequently?
Bethell's latest complaint? That evolution's "central claim" is "unlimited variation" and that this unlimited variation "has not yet been observed".
The first claim is simply false. Evolution is heritable change in a population over time. The theory of evolution describes the mechanisms (mutation, natural selection, sexual selection, genetic drift, founder effects, etc.) that explain how this change takes place. Speciation has been observed, so the usual creationist claims that evolution is limited to change "within species" have been thoroughly discredited.
But the funny part is Bethell's second claim: that unlimited variation has not yet been observed. What would it mean to observe unlimited variation? At what point could we put our foot down and say, "Hey, now we know that unlimited variation has finally been observed!"? The whole meaning of the word "unlimited" is that it is without bound. It's like alleging (incorrectly) that the central claim of cosmology is that the expansion of the universe goes on forever, and then saying "That endless expansion has not yet been observed!"
What we do see is evolution taking place today, and we have the fossil record that shows the changes in the past. You have to be particularly dense or dishonest to deny this.
Please, Tom, keep it up. You're our best friend.