Thursday, June 02, 2005

Are we still in Kansas?

Francis Crick, one of the discoverers of the structure of the DNA molecule, has wondered whether life on this planet might have been deliberately seeded by advanced space aliens. A science-fiction scenario like this is plausible, even if unlikely. But how might we go about testing such a theory in the absence of any direct evidence, such as an ancient alien base on the far side of the moon, complete with interstellar Rosetta Stone? And what might lead us to the space-alien theory in the first place? Crick was led to his theory of directed panspermia by the difficulty of explaining how life could have arisen on Earth. If the problem of accounting for the origin of life on this planet were to persist, and become intractable, then panspermia--perhaps even directed panspermia--might eventually be seen as the best explanation. We might come to accept the likelihood that life on this planet was designed by intelligent non-humans. And we just might be right to do so. (Of course, there is the problem of explaining how the alien life forms might have originated. The theory of cosmic ancestry is a version of panspermia that holds that life has always existed in the universe.)

Perhaps you can see where this is going. In Kansas these days, and in other places, particularly in the United States, the debate is raging over whether Intelligent Design should be taught alongside Darwinian theory in schools. And the proponents of Intelligent Design are not talking about space aliens. They believe not only that Darwinian natural selection cannot account for the origin of complex living systems, but that the reasonable inference to draw is that such systems can only have been designed by a supreme intelligence: God. They claim that, in the interest of fairness and open-mindedness, students should be taught about Intelligent Design as well as about Darwin, and should be told that evolution by natural selection is "only a theory".

I think that there's a place for discussing Intelligent Design in schools, but that place is not science courses. Intelligent Design is a modern version of what's called the Argument from Design. In its most famous form, this argument says that if you found a watch lying in a field, opened it up, examined its intricate mechanism, and understood that this intricate mechanism functioned to keep track of the time of day, you would have no hesitation in ascribing the origin of the watch to an intelligent designer. And you would be right to do so. Similarly, if we understand the amazing complexity of the natural living systems around us, which far exceed in sophistication anything invented by humans, we ought not hesitate to attribute them to a supreme intelligence.

Advocates of Intelligent Design may claim that Darwin's theory of evolution by natural selection is inadequate because it does not make testable predictions, or they may say that if Darwinism is good enough to be called science, then Intelligent Design should be considered good enough too. For their part, those who deride Intelligent Design often claim that Darwinism does make testable predictions. They say, for example, that it predicts change in species over time. The problem with that one is that Darwin himself wrote in The Origin of Species, "I no law of necessary development." Change is always possible, but not necessary. Also, Darwinian theory does not specify just how species will change over time, when they do change. It cannot say, "Three and a half million years from now, horses will have evolved to have a single horn growing from the middle of their foreheads." Nor can it retrodict the exact forms of the ancestors of existing creatures. Defenders of Darwin sometimes claim that his theory is scientific because it is "falsifiable"--not that it is false, but that there are certain conceivable empirical occurrences that, if true, would show the theory to be false. The one I've heard more than once is that finding a fossil hominid in the Pre-Cambrian geological record would show Darwin's theory to be false. Personally, I believe that good fairies keep the flowers growing. Because of this, I am perfectly prepared to say that, if flowers don't bloom next spring, my good-fairy theory will be blown to bits, and I claim on this basis that my theory is testable and therefore scientific.

Obviously, that won't do. No one expects to find fossil hominids in the Pre-Cambrian record, whether they are Darwinists or not. Karl Popper, the philosopher of science who argued for falsifiability as the mark of science, insisted that in order to count as testable, a theory has to make risky predictions--that is, it has to predict observable results that we would not otherwise expect. ("Wow, it's spring and the flowers are actually blooming. I never would have believed it! I guess there may be something to that good-fairy theory after all.") It is not clear that Darwinian theory makes any risky predictions. But that doesn't mean it isn't good science. Darwin provides us with an explanatory mechanism that plausibly accounts for the historical record: for the change from one state of affairs to another according to lawful regularity (even given that the regularity subsumes random changes in an organism's genetic constitution). Darwinism may not be the last word in explaining the history of life on this planet, but it remains a fruitful scientific theory. (Why should we imagine that any scientific theory is the last word?) On the other hand, Intelligent Design, insofar as it appeals to arbitrary acts of will on the part of a designer, is not science--even if it is true. Science, by its very nature, explains phenomena by appeal to lawful natural regularities. So even if we were eventually forced to conclude that the best explanation for the origin of living forms on Earth was one or more interventions by space aliens or by God, what we would be left with in this regard would not be "Intelligent Design science" or "Creation science", but no science at all. That's why Intelligent Design belongs in philosophy or religion classes, but not in science classes.
It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. ... There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
Charles Darwin
Sept. 26 update: Here's a piece that indicates Darwinian theory does make risky, testable predictions.

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