It just occurred to me ....
Probably a stupid question, but I'm sure somebody will set me straight if necessary. Did anybody ever establish whether there was in fact a genetic basis for industrial melanism in peppered moths?
Could it be possible, for example, that the expression of melanism was due to the presence of higher levels of carbon and pollutants in the diet of the moths? This might be earlier in the lifecycle of the moths, or even possibly in the lifecycle of ancestor moths.
One of the implications of this is that it would undermine the case made for natural selection. Rather than a random distribution of light and dark moths, with differential predation at work subsequently changing the distribution and leading to a shift in the population (the natural selection paradigm), such developmental changes would result in a non-random distribution of light and dark moths in different environments, regardless of predation.
Was this possibility excluded at the time? Has it been since?