This was seen quite clearly when specimens collected about 1880 were compared with specimens collected more recently: clearly the dark morph has been adjusted by the strong selection acting on the gene complex.
Isto viuse claramente cando espécimes recollidos arredor de 1880 foron comparados con espécimes recollidos recentemente: claramente o morfo negro axustouse á forte selección que actúa sobre o complexo do xene.