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"In my opinion the greatest error which I have committed, has been not allowing sufficient weight to the direct action of the environment, i. e. food, climate, etc. independently of natural selection. Modifications thus caused, which are neither of advantage nor disadvantage to the modified organism, would be especially favoured, as I can now see chiefly through your observations, by isolation in a small area, where only a few individuals lived under nearly uniform conditions.

When I wrote the 'Origin of species' and for some years afterwards, I could find little good evidence of the direct action of the environment. Now there is a large body of evidence and your case of the Saturnia is one of the most remarkable of which I have heard."