The two main arguments that Intelligent Design proponents support to prove that a supernatural force has created everything in life are the following:
The first argument is Irreducible Complexity. Irreducible Complexity holds that biochemical parts in nature have complex parts that are interdependent with other parts. If you take one part, the whole system does not work. Therefore, these systems cannot be the result of evolution. Darwin claimed that if Irreducible Complexity can be proved, his natural selection theory will fail. But an argument on Irreducible Complexity is that the complex organ or part could have been contained of smaller parts. An example of that is atom. Atom is the smallest component of an element, while atom itself is made up of smaller components. Therefore, it can be concluded that Irreducible Complexity does not have enough explanation to be accepted.
The second argument for people who are in favor of intelligent design is specified complexity. This argument is made by a mathematician named William Dembski. He suggests non-random patterns of information are ubiquitous in nature and he calls it complex specified information. An example of complex specified information is DNA. DNA is made up of four chemical repeating bases arranged into complimentary pairs. The bases can be strung together to form genes. Therefore, DNA is specific and complex. Furthermore, the reason that human never gives birth to a human and not a chimpanzee shows that DNA is specific. Complex specified information is an evident of intelligent design.
Yet scientists believe that evolution theory is the only theory that explains how complexity is made from simplicity in nature. Evolution theory seems more reliable than intelligent design concept because it can be observed in living beings whereas intelligent design is not observable.