In the case of living machinery, the ‘designer’ is unconscious natural selection, the blind watchmaker. - Richard Dawkins

Natural selection is like artificial selection, but without the human chooser. Instead of a human deciding which offspring shall die in which shall reproduce, nature ‘decides’. The quotation marks are vital because nature doesn’t consciously decide. This might seem too obvious to emphasize, but you’d be surprised by the number of people who think natural selection implies some kind of personal choice. They couldn’t be more wrong. It just is the case that some offspring are more likely to die while others have what it takes to survive and reproduce. Therefore, as the generations go by, the average, typical creature in the population becomes ever better at the arts of surviving and reproducing. Ever better, I should specify, when, when measured against some absolute standard.

Let children learn about different faiths, let them notice their incompatibility, and let them draw their own conclusions about the consequences of that incompatibility. As for whether they are ‘valid,’ let them make up their own minds when they are old enough to do so.

Real life seeks the gentle slopes at the back of Mount Improbable, while creationists are blind to all but the daunting precipice at the front.