Good article by science writer Carl Zimmer, explaining the nature of a theory in the scientific sense of the word. Evidently, this is very much misunderstood by the general public. Carl Zimmer is a wonderful author. In addition to his articles and blogs he has written multiple superb books, including Parasite Rex and Soul Made Flesh.
n.b. Parasite Rex is not for the faint of heart!
Check out his web page http://www.carlzimmer.com/