I assume it will be granted by everyone that, even though the past cannot be directly observed, a scientific argument against the Darwinian theory of evolution is not impossible. If it were impossible, that would cast doubt on whether the theory is itself science. The theory makes claims about the causes of evolution that are inferred from the available evidence, and that could be undermined by further evidence. For example, as we learn more about the behavior of the genetic material, and more about how the properties of organisms depend on it, it will be possible to give more precise answers to questions about the rate at which viable mutations can occur randomly as a result of physical accident, the kinds of phenotypic changes they can generate, and the number of generations within which specific changes would have had to occur to make the theory fit the development of organisms as we know them. Together with calculations of the numbers of individual organisms that have been involved in the major transitions in evolution, this should make it possible to evaluate the theory mathematically.
Most evolutionary biologists are confident about the answers to these questions, but there is no a priori guarantee that they will eventually be answered in a way that confirms the theory. One of the disturbing things about the public debate is that scientists engaged in it sometimes write as if the idea of fundamental problems with the theory (as opposed to problems of detail in its application) were unthinkable, and that to entertain such doubts is like wondering whether the earth is flat. This seems to me, as an outsider, a vast underestimation of how much we do not know, and how much about the evolutionary process remains speculative and sketchy. Since it is a scientific theory that makes large claims about what cannot be directly observed, there could be scientific evidence against it (and new evidence is constantly becoming available in this case, since molecular biology is so new).
(Thomas Nagel, "Public Education and Intelligent Design," Philosophy & Public Affairs 36 [spring 2008]: 187-205, at 190-1)
Note from KBJ: Nagel will be attacked for writing this. (For all I know, he already has.) He will be charged with giving aid and comfort to the enemy. It will be said that he should keep doubts about evolution to himself, so as not to induce doubt among laypeople (as though laypeople read Philosophy & Public Affairs). There is more dogmatism among biologists than among all the theologians the world has ever known. It's disgraceful. Dogmatism is antithetical to science.
Note 2 from KBJ: I discovered this during a Google search. The author, who calls Nagel "dangerously naive," says that Nagel doesn't understand either science (ouch!) or the motives of those who urge that Design Theory be taught in public-school biology courses. What do motives have to do with anything? Nagel is a philosopher; as such, he's interested in reasons, not motives. He wants to know whether there are good reasons to exclude Design Theory from public education.
Note 3 from KBJ: The author of the criticism doesn't grasp the implications of what he is saying. He says that science "by definition" rules out supernaturalistic explanations. But this definition of "science" is not itself part of science; it is what draws the boundaries of science. How does that differ from faith? The larger issue is this. The word "science" (from Latin scientia) means knowledge. By limiting themselves to naturalistic explanations of data, scientists such as the author cut themselves off from knowledge, should there be any outside the artificial realm of naturalism. They're playing a special game—call it the Naturalistic Game. That's fine. What they cannot do is say that (1) there are no other games worth playing or (2) their game is the only game that has truth as its goal.
Keith Burgess-Jackson, J.D., Ph.D. 