wouldn't 6,000 years of natural selection have removed it from the gene pool before pollution made it beneficial?
Yeah, especially since it is part of a fairly large genus,
Biston, that presumably diversified rapidly after the flood into 54 species and 40 subspecies culling alleles at every population split / speciation event. It's lucky it has any alleles at all.
HBD
Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for... I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca
"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.
Ignorance is a most formidable opponent rivaled only by arrogance; but when the two join forces, one is all but invincible.
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