The peppered moth (Biston betularia) is the classic example of natural selection observed in a real population.The moth rests on tree trunks during the day. Before the Industrial Revolution almost all peppered moths in Britain were the pale, speckled form, which was camouflaged against pale, lichen-covered bark. A rare dark (melanic) form, called carbonaria, is caused by a single dominant allele and was first recorded near Manchester in 1848.During the Industrial Revolution, soot from coal burning killed the lichens and blackened tree trunks near industrial cities. This changed the selection pressure:1. Insect-eating birds prey on resting moths. Predation is the selection pressure.2. On dark bark, pale moths were easily seen and eaten, while dark moths were camouflaged.3. Dark moths were more likely to survive and reproduce, passing on the dark allele.4. The frequency of the dark allele rose rapidly. By the end of the nineteenth century, well over 90% of peppered moths around Manchester were dark.After clean air laws in the 1950s reduced soot pollution, lichens returned and bark became paler. The selection pressure reversed, pale moths were favoured again, and the dark form has now become rare.Experiments in the 1950s by Bernard Kettlewell, who released and recaptured marked moths, supported this explanation: more pale moths were recaptured in unpolluted woods and more dark moths in polluted woods.