The secret behind a genetic mutation that led to the original speckled version of the peppered moth being replaced by a black variety has been uncovered. The answer lies in Britain's Industrial Revolution. Jim Drury reports.
This is how the peppered moth appeared before Britain's Industrial Revolution - and this is how it looked 30 years into that period of huge transition. Evolutionary biologist Dr Ilik Saccheri.... SOUNDBITE (English) DR ILIK SACCHERI, EVOLUTIONARY BIOLOGIST AT LIVERPOOL UNIVERSITY, SAYING: "The first black form was recorded in Greater Manchester in 1848, but by the turn of the century - which is to say around 1900 - virtually all of this type (speckled) was gone from the north west and industrial regions of Great Britain and they had been entirely replaced by this form (black)." The black insect thrived by blending in with sooty tree bark to avoid avian predators. Saccheri's team found a 'jumping gene' mutation to be responsible for the change. SOUNDBITE (English) DR ILIK SACCHERI, EVOLUTIONARY BIOLOGIST AT LIVERPOOL UNIVERSITY, SAYING: "The type of mutation that we've discovered is called the transposable element - or colloquially sometimes referred to as a 'jumping gene', which is a large piece of DNA that copies itself from one location in the genome and then pastes itself into another location in the genome; and it's caused a disruption in the gene into which it's inserted itself." The mutation may have existed at low frequencies for hundreds of years. By using DNA sequences Saccheri dates the mutation to black to 1819. After the UK government passed clean air acts in 1956 and 1963 the gradual lightening of the environment saw the black moth decline, and the speckled variety re-appear. Saccheri says the findings offer a complete example of evolution by natural selection.