There continues to be a great deal of confusion, much of it seemingly deliberate, over the nature of the Intelligent Design (ID) hypothesis as well as the nature of the basic assumptions of Darwinian evolution (DE) and creationism (C). This post is an attempt to clarify things a little.
Let's start with the commonly heard refrain that DE is science whereas ID is religion.
The fundamental claim of DE is that all of life has arisen solely as a result of blind, unguided, impersonal processes. ID is, in its essence, simply the denial or contrary of this claim. ID states that mechanistic processes are inadequate by themselves to account for what we find in the realm of living things and that one of the causal factors which must be invoked to fully account for life is intelligence. Whatever philosophical status the basic assertion of DE enjoys its contrary also enjoys, and vice versa. If the proposition that life is completely explicable in terms of blind, impersonal processes is a scientific assertion then so is it's denial. If the proposition that life bears the impress of intelligent purpose is religious then so is it's contrary.
ID is not C. Creationism is an attempt to vindicate the Genesis account and to reconcile it with science. It starts with the assumption that Genesis is true, and it will not accept any explanation that is incompatible with this assumption.
Similarly, DE starts with the assumption that only naturalistic forces can be employed to account for living things and will not accept any explanation which is incompatible with this assumption.
Both C and DE are inferences from an a priori metaphysical commitment and are more like each other in this regard than either is like ID.
ID starts with observations of living things and infers from the empirical data that intelligence must have played a role in the development of life. As such, ID is an observation-based hypothesis and is therefore more scientific, in this sense at least, than either of its competitors. It's inference that purpose and intentional design underlie life on earth is based not on a presupposition that there is a designer (though many ID theorists doubtless hold such a presupposition in their private lives), but rather upon several obvious facts about the world. Here are three:
1) The abundance of specified complexity (information) in the biosphere: Information is not generated by purposeless processes. A computer, for example, does not produce simulated organisms by blind chance. The computer must be programmed to follow an algorithm which is itself the product of intelligence. Likewise, DNA and proteins which carry far more information than does the average library, are not adequately explained by purposeless processes any more than are the books in the library.
2) The existence of ostensibly irreducibly complex structures and processes: If irreducible complexity exists in living things - and despite the claims of critics, no one has been able to put forward a convincing case that it does not - then this would be evidence of an intelligent agent at work. The nature of biochemical machines and pathways, cellular assembly lines and factories, and highly complex chemical cascades (like blood clotting) all point to purpose. The idea that these things could have arisen through random mutations and natural selection apart from any intentional engineering would be regarded as extremely implausible were it not necessitated by a prior commitment to materialistic explanations.
3) The telic nature of the cosmos: That life is telic (i.e. evinces purpose) is in dispute. That the cosmos is telic is much more difficult to gainsay. Cosmologists can invoke no mechanism like natural selection to explain the exquisite fine-tuning that is being discovered to exist throughout the warp and woof of the cosmos. If the cosmos as a whole bears witness to having been intricately engineered for a purpose, it is plausible to think that certain aspects of the cosmos, like the structures in living things, which appear to be designed for a purpose, actually are.
Indeed, we must keep in mind that the current debate is not about whether there is design in the biosphere. Everyone agrees that there is. The debate is over the source of that design. Is it nature blindly selecting for survival advantage, or is it an intelligence of some kind, a "World Soul", a Platonic demiurge, an idealist "Absolute", or the God of classical theism? ID offers no opinion.
It must be stressed that, strictly speaking, ID does not conflict with evolution (E), the theory of descent by modification. It conflicts only with DE, which insists that descent is a thoroughly naturalistic, mechanistic process. E simply asserts, however, that organisms share common ancestors. It does not require one to believe that the process of descent from these ancestral forms was purely mechanistic.
Thus there are among the top ranks of ID advocates a number of evolutionists of various stripe, and there are also some who are more creationist in their beliefs. ID is compatible with both, although either, or both, could be wrong and ID would be unaffected. What ID is not compatible with is DE.
ID is scarcely even related to C except insofar as both theories hold that an intelligence was involved in the emergence of life. To see the vast difference between them one need only realize that all of Genesis could be proven wrong but, although C would be thoroughly devastated, the theory of ID would be unscathed. ID is not dependent upon Genesis or any other religious or metaphysical book or doctrine for its content.
Contrary to the insistent claims of its critics, and the hopes of some of its advocates, ID is not religious. It requires no commitment to a god, it prescribes no worship nor doctrine. It has no clergy nor holy books. It simply holds that blind, unguided processes are inadequate by themselves to account for living things and that at some point, in some way, intelligence must have played a role. This is hardly a religious assertion, and unlike religious assertions, may even lend itself to testing. If it could be shown, for instance, that some mechanistic process does indeed produce information or an increase in information, if it could be plausibly and convincingly demonstrated that DNA or proteins could have arisen by chance through purely natural processes, then intelligent agency will have been shown to be a superfluous add-on, and ID will be decisively refuted.
Some may wish to use ID as a wedge to get religion into schools, but ID should be judged on its merits and not on the motives of some of its proponents. There are some who insist, after all, that DE be taught because they see it as a way of inculcating atheism into students. There are others who have used DE to justify social Darwinism and even genocide. It would be an error to judge DE on the basis of such misuses by its votaries, and it's equally wrong to judge ID by the misuses to which some of its adherents wish to put it.
There can be no harm, despite the hysteria of the ACLU and its allies in the scientific community, in informing students, when they are studying evolution, that although many scientists believe the process requires only mechanistic engines like mutation and natural selection, others disagree. It hurts no one to inform students that there are many scientists and philosophers who believe that whether evolution accurately describes how life came to be or not, the fundamental causes of life must have included intelligent purpose among them.