Doesn evolution depend on mutations and aren most mutations harmful?
No. Most mutations are neither harmful nor helpful. That’s the short answer. The long answer is that mutations can be neutral (neither helpful nor harmful), strictly harmful, strictly helpful, or (and this is important) whether they are harmful or helpful depends on the environment. Most mutations are either neutral or their effect depends on the environment. Let’s look at an example of a mutation which may be harmful or helpful, depending upon circumstances. English peppered moths come in two varieties, light and dark. Before the industrial revolution dark moths were very rare. During the worst years of the industrial revolution when the air was very sooty dark moths became quite common. In recent years, since the major efforts to improve air quality, the light moths are replacing the dark moths. A famous paper by H.B.D. Kettlewell proposed the following explanation for this phenomenon: Birds eat the kind of moth they can see the best. In England before the Industrial Revolution trees
