Melanisation in peppered moth is an observation that 

In a collection of moths made in 1850s (in England), i.e., before industrialisation set in, it was observed that there were more white-winged moths on trees than dark-winged or melanised moths. However, in the collection carried out from the same area, but after industrialisation, i.e., in 1920, there were more dark-winged moths in the same area, i.e., the proportion was reversed. This is an interesting observation that supports evolution by natural selection.