Cor, wish I hadn't mentioned the dreaded peppered moth... There are plenty of question marks over the integrity of the initial study of this poor beast. As for being an example of evolution, that's tricky. The dark form was present all along, but in low numbers, then a change in the environment favoured it, so its numbers increased. Natural selection. But the only way in which the species has changed is in the relative numbers of dark and light forms, and, if the environment changes back, this change is completely reversible.