People often say that evolution is “only a theory.”  It’s important to remember that the term “theory” in science is not the same as it is in general usage.  A scientific theory is a unifying concept that explains a large body of data.  It is a hypothesis that has withstood the test of time and the challenge of opposing views. The Theory of Evolution is the basic unifying concept of biology.  The CEO of The American Association for the Advancement of Science, Alan Leshner, wrote, “Although scientists may debate details of the mechanisms of evolution, there is no argument among scientists as to whether evolution is taking place.”  The National Academy of Sciences, the most prestigious scientific organization in the United States, has declared evolution “one of the strongest and most useful scientific theories we have,” and notes that evolution is supported by an overwhelming scientific consensus.  The Theory of Evolution has as much validity as the theory of gravity, atomic theory, or the germ theory of disease.  It's interesting to note that the idea that the Earth goes around the sun is also a scientific theory — albeit one with extensive evidence.  Every day our eyes are deceived, when we see the sun rising and setting as it apparently goes around the Earth.

Evolution is thus both a fact and a theory.  It is a fact that species have evolved.  The Theory of Evolution explains our best understanding of the processes that cause evolution.  It's a lot like gravity.  Gravity is obviously a fact.  The theory of gravity attempts to explain how gravity works.  Actually, we know less about how gravity works than how evolution works.

There is an underlying problem with the design argument, and most proponents of Intelligent Design probably aren’t aware of it.  By assuming that living things have some sort of metaphysical purpose, they are intrinsically assuming what they want to prove.  Purpose is an abstract human concept that exists only in our minds, much like beauty — with no physical reality.  In the universe things have no intrinsic purpose; they just exist.  Does an atom have any purpose?  Does a pebble?  Does a star?  Does an amoeba, plant or any living thing have a real external purpose?  We could say that living things have the purpose of procreating to continue their species.  However, we must realize that this is just our viewpoint, our interpretation.  Rocks, trees, people, stars, and the universe have no intrinsic purpose.  We can create purpose for ourselves, and that is good because it's a useful concept; but it’s important to understand that purpose is a human construct.  Remember, when proponents of ID begin their arguments by noting the design and purpose of nature, they are assuming what they want to prove.  Don’t be fooled by this logic sleight of hand.  No intelligent designer is needed for purpose to exist, because purpose exists only in our minds.