Peppered history

Jerry Coyne points to a story in Current Biology by Adam Hart and colleagues, which suggests that Darwin missed the chance to identify industrial melanism, eighteen years before it was first noticed by James William Tutt:

Theres no evidence that Darwin answered Farns letter, but of course he had voluminous correspondence with hundreds of people, and its too much to fault the old man for failing to follow up on this one suggestion. And even had he done so, that might not have hastened the general acceptance of natural selection, which after all was not widely embraced by evolutionists until around 1930. Nevertheless, its interesting to contemplate Darwins reaction as he read this letter. Did he blow it off? Or did it simply get lost in the welter of his correspondence?