a, Frequency of the carbonaria phenotype from ~1800 to 2009. b, Corresponding frequencies of the carbonaria allele. The envelopes show the confidence intervals (50%, 90% and 99%) for the simulated trajectories. Dark-red dots, observations falling within the simulated trajectories; orange dots, additional data collected after 2002 (year during which >85% of the field sample was collected). Stars indicate likely frequencies where historical data are scarce. Data and sources are listed in Supplementary Table 3.