What's in a Theory?

Red State Rabble has an interesting post on the relative "theoryness" of Evolution and Intelligent Design. (See Coyne's excellent piece in The New Republic for a more detailed discussion of the same problem.) Hayes hit the nail on the head with his analysis of why Darwin, and not Empedocles or your favorite proto-evolutionist, is given the lion's share of the credit for discovering evolution:

There were others, many others, who observed the fact of evolution and wrote about it, as well.

Why then, does Darwin get all the credit?

The answer is really quite simple. The name of Charles Darwin and the theory of evolution, which he called descent with modification, will always be inextricably linked because he explained how evolution works.

A similar phenomenon occurred in Geology. Alfred Wegener proposed continental drift (CD) a good 50 years before it gained widespread acceptance within the scientific community. It took the development of the theory of plate tectonics in the late 1960s, which provided a plausible mechanism for CD, for geologists to accept it. In fact, CD had long provided a better explanation for some of the data, such as patterns in biogeography, and the shapes of the continents had CD written all over them, but that wasn't enough. Similarly, Lamarck's reasonable arguments failed to persuade the majority of the naturalists of his time that evolution had happened. However, in both cases, the scientific consensus changed almost overnight. Huxley famously remarked upon reading "On the Origin of Species": "how stupid of me not to have thought of that." That feeling has recurred ever since.

Naturally, some proponents of ID would like to think that ID is the new CD. (Orac has noted that this is a line of argument favored by various pseudo-scientists and cranks -- he calls it the Galileo Gambit and he Knows...) That is pure wishful thinking on their part. As I said, there was plenty of evidence in favor of CD before it was adopted. In contrast, as Coyne points out:

Insofar as intelligent-design theory can be tested scientifically, it has been falsified. Organisms simply do not look as if they had been intelligently designed. Would an intelligent designer create millions of species and then make them go extinct, only to replace them with other species, repeating this process over and over again? Would an intelligent designer produce animals having a mixture of mammalian and reptilian traits, at exactly the time when reptiles are thought to have been evolving into mammals? Why did the designer give tiny, non-functional wings to kiwi birds? Or useless eyes to cave animals? Or a transitory coat of hair to a human fetus? Or an appendix, an injurious organ that just happens to resemble a vestigial version of a digestive pouch in related organisms? Why would the designer give us a pathway for making vitamin C, but then destroy it by disabling one of its enzymes? Why didn't the intelligent designer stock oceanic islands with reptiles, mammals, amphibians, and freshwater fish, despite the suitability of such islands for these species? And why would he make the flora and fauna on those islands resemble that of the nearest mainland, even when the environments are very different? Why, about a million years ago, would the designer produce creatures that have an apelike cranium perched atop a humanlike skeleton? And why would he then successively replace these creatures with others having an ever-closer resemblance to modern humans?

There are only two answers to these questions: either life resulted not from intelligent design, but from evolution; or the intelligent designer is a cosmic prankster who designed everything to make it look as though it had evolved. Few people, religious or otherwise, will find the second alternative palatable. It is the modern version of the old argument that God put fossils in the rocks to test our faith. [...]

Herbert Spencer could have been describing ID when he declared that "those who cavalierly reject the Theory of Evolution as not being adequately supported by facts, seem to forget that their own theory is supported by no facts at all. Like the majority of men who are born to a given belief, they demand the most rigorous proof of any adverse belief, but assume that their own needs none."

ID has to come up with some evidence and testable predictions. Until it manages to do so, it cannot be considered a scientific theory at all.