A mutation is a change in a nucleotide, copied in the next generation, which breeds true. Since mutations are random nucleotide changes, most of them are harmful or lethal, coding into existence nonfunctional enzymes. It is a long wait before a mutation makes an organism work better. And yet it is that improbable event, a small beneficial mutation in a nucleotide a ten-millionth of a centimeter across, that makes evolution go.
