However, one aspect of evolutionary theory is "natural selection", and in certain limited cases dealing with changes within a species, natural selection is in fact "more than a hypothesis."  For example, some studies have shown that beak sizes in finches can vary depending on selection due to environmental factors.  The same phenomenon of variation has been found in classical studies of the survival value of changes in wing coloration of peppered moths. Yet, in the end, we still have finches and peppered moths.   The changes are due to natural selection and the environment acting on variations in the genetic information within members of a species.

However, the aspect of evolutionary theory that is most often questioned and debated is the supposition of "common evolutionary descent." It is questionable because there is no experimental, scientific proof that one species or family has descended from another. It is merely a hypothesis, and has not progressed beyond this stage for a century and a half. The term evolution in this essay will refer to this concept of common evolutionary descent.

In recent years the work of scientists who employ intelligent design theory has effectively debunked the notion of neo-Darwinism, i.e. evolution of new species arising from the interaction of natural selection, the environment, and genetic changes primarily due to mutations. Among the active pioneers in the intelligent design community are the London-educated Michael Denton, and the Americans William Dembski, and Michael Behe, a Catholic. Nevertheless, the new developments that have effectively challenged neo-Darwinism have not prevented evolutionists from brazenly referring to their model as the "fact of evolution." But evolutionary descent can be labeled neither a fact, nor as "more than a hypothesis", since it has never been scientifically proven that higher animals and plants developed from other species or simpler forms of life. Controlled laboratory experiments on genetic mutations have failed to produce evidence of new species evolution or even an "improved version" of an existing species.