All scientific conclusions are probability statements: an observation is repeated a number of times and, say, nine times out of ten the results confirm a given idea, so . . . the idea is thrown out. A ninety percent chance of being right is not good enough. The probability of being right has to be nineteen out of twenty in the biological sciences. It has to approach ninety nine out of a hundred in the physical sciences. Imagine applying those standards in your personal life.

In science, that's just the beginning. The hypothesis, which is an expensive word for educated guess, is merely said to be confirmed once it passes that bar. These guesses are dignified with the name of "theory" when they have been confirmed so many times there is no real chance they won't continue being confirmed. They are called "laws" when that certainty becomes crushing, but even laws are probability statements. The law of gravity is a probability statement with an extraordinarily low chance of not working.

Against that backdrop, evolution is called a theory because there are so many facts in its favor. It's a parallel case to our understanding of stars and electrons. We have no personal experience of any of them, but scientists who have studied the facts have come up with coherent explanations that pan out. Evolution can explain practical things, such as how bacteria develop antibiotic resistance and why measles epidemics run in cycles, and it can provide mind-altering insights such as that insects and mammals have the same basic body plan, except the plan is back to front.

None of the other ideas for explaining the patterns of life rests on any facts that contradict evolution. The theory of intelligent design (and "theory" is used here in its common meaning) has not been able to show the existence of intelligence in the design, using scientific methods. Creationists can't show that creation occurred. If the scientific method is not used, the result is not science.

People who argue against evolution can, and do, fit some of the facts into their theories, but they have to ignore all the facts that disagree, which is about as far from the scientific method as you can get. They have no measurable observations and no testable, independently verifiable predictions.