Intelligent design (ID) is in part a political phenomenon, created because the United States Courts rejected the teaching of creationism, and then 'creation science', as science in the school syllabus. The proponents of intelligent design believed that, by separating claims for the existence of God from their hypothesis about design of living organisms, the courts would accept ID as a suitable topic for a science course, taught alongside, or instead of, evolution.
According to intelligent design proponents, the specified complexity exhibited in living forms demonstrates that blind natural forces could not by themselves have produced those forms but that their emergence also required the contribution of a designing intelligence.
According to a leading advocate, William A. Dembski, intelligent design attaches no significance to questions such as whether a theory of design is in some ultimate sense true, or whether the designer actually exists or what the attributes of that designer are. He says intelligent design makes no claims about the origin or duration of the universe, is not committed to flood geology and can accommodate any degree of evolutionary change - as long as there is a designer guiding that evolutionary change. Intelligent design is compatible with the creationist idea of organisms being suddenly created from scratch, but is also perfectly compatible with the evolutionist idea of new organisms arising from old by a gradual accrual of change.
Unlike other creationists such as Michael J. Behe, Dembski believes that complex microbiological systems, such as the bacterial flagellum, could have evolved from random changes, as long as there was a guiding designer. Dembski says that intelligent design is a hypothesis worth investigating even if there is as yet no evidence for it.
In Questions about Intelligent Design, Dembski says, "Most evolutionists hold that the Darwinian mechanism of natural selection and random variation introduces novel specified complexity into an organism, supplementing the specified complexity that parents transmit to their offspring with specified complexity from the environment. [my emphasis]." He thus demonstrates a failure to understand the basics of the Theory of Evolution by Natural Selection, which does not conceive natural selection and random variation introducing any novel complexity into an organism unless this was transmitted from its parents. The intelligent design concept is fundamentally flawed and has not been accepted by the United States courts as genuine science.
Although ID has undoubtedly become a somewhat political phenomenon, it did not begin this way. Philip Johnson, another promoter of ID conceived of it, as do others such as Michael Behe as a concept which is critical in a negative sense of existing evolutionary paradigms. The evidence used by Behe relates to the possibility of complex biological systems, which he describes as irreducibly complex, arising by the chance mechanisms of evolution. Since all the parts of these systems are required to be in place for the sytem to operate, the process of natural selection would select against the devlopment of these complex systems while they were being 'built' by the slow and gradual process of evolution.
In this sense, ID was put forward largely as a critique of evolution and points to a number of different examples which are inexplainable under current evolutionary thought. Currently there is no scientific explanation as to how the genetic information required to 'build' these structures could arise spontaneously through evolutiuonary processes.
Further to this, the science of genetics, in line with the laws of thermodynamics point to mutations as unable to add new genetic information, although recombination and duplication certainly occur, as well as certain genes being 'switched off' or 'on' with resultant effects in living things. ID theorists, although themselves criticizing evolution, or the current understanding of it, in turn come in for criticism from both evolutionists and creationists alike. The former, because they are criticizing the theory of evolution, the latter for the ID theorists reticence to name the designer.