Evidence
ID-proponents such as
Michael Behe promote theories such as "
irreducible complexity" as evidence for their ideas. Irreducible complexity posits that there are certain organs and structures found in nature that have no convincing gradual evolutionary pathway, and are too complex to have come about in whole by chance. These ideas are hotly disputed (or dismissed as non-science) by scientists, but regardless of their truth value they do not constitute evidence for an intelligent designer. Proponents of intelligent design make an assumption unwarranted by the evidence in that their logic goes along the lines of "The origins and diversity of the species cannot be accounted for by evolution and natural selection alone, therefore there must have been a designer involved."
The very
lack of positive scientific evidence suggesting that there is a designer involved in creating life raises the question of how the design hypothesis came about. Opponents of the design hypothesis would suggest that proponents are religiously motivated, and that their ideas are not about understanding how life came to exist but rather about promoting a particular religious world view - as espoused in the Wedge Document.
One problem with finding evidence for intelligent design is the inability to distinguish "naturally" evolved mechanisms from "designed" mechanisms. Nobody knows what the "design" of a supernatural creator looks like; how can we tell what was and was not designed?