In The God Delusion, Dawkins discusses evolutionary by-products. The example he chooses to use is a moth flying into a flame as a demonstration of what we see as abject stupidity. Why would a moth deliberately fly into a flame?

This is not an example of natural selection….it is an example of natural selection gone wrong. Moths evolved to fly at night by using celestial objects as guides: Keep the light source in a certain position and you can navigate, much as we do with a compass which points north. Dawkins notes that it was not until comparatively late in evolutionary history that there was anything like artificial lights to throw off the moths. We see only the moths who get distracted by the flames. We do not see millions of moths who merrily go on their way without self-immolating themselves.