Described as industrial melanism, during the Industrial Revolution when the iconic viaducts were built, the peppered moths (bison betularia) feeding on soot blackened lichen were eaten by predatory birds.

Meanwhile the all-dark individuals became more dominant in their population as they were camouflaged against the sooty lichen. Since the Clean Air Act of 1956, the population of all-dark biston betularia moths has all but disappeared whilst the peppered moth has seen a rise in population. 

Georgie Phipps