Proponents of Intelligent Design point to complex biological structures such as the eye, bird's wings, the existence of mitochondria, etc., arguing that such structures could not have possibly have developed due purely to random mutations, even with the aid of natural selection. Symbiotic relationships, such as plants who can only be pollinated by a specific species of insect, which in turn can only reproduce by using the plant, could not have arisen, they argue--a typical chicken-and-egg problem. It is argued that these kinds of biological features are by their very nature too interdependent to come into existence independently through a natural process and then become as intricately intertwined.
Some Intelligent Design arguments fall to later scientific study. For example, the development of mitochondria was once puzzling, but [Lynn Margulies]?'s theory of their evolution from endosymbiotic bacteria, once rejected even by biologists, has amassed enough evidence that it is now widely accepted. Evolutionary development of such structures as eyes and wings has been simulated in computers. Studies of [fig wasp]?s have revealed how symbotic species can evolve. Most scientists assume that all "problems" that Intelligent Design proponents show will be similarly resolved with further progress of science.
Not all people who believe that God was involved in the design of the Universe also adhere to the specifics of Intelligent Design theory as proposed by Creationists.
Intelligent Design has lately been a controversial subject, particularly in American schools. After years of Judicial rejection of Creationist teaching--on the grounds that Creationism is a religious, not a scientific theory--many Creationists have begun to promote Intelligent Design as a non-religious, scientifically acceptable alternative to the theory of Evolution.