43i 
But this is not all. For when Mr. Darwin acknowledges 
that he has not paid sufficient attention to the influence of 
changed conditions, what does he add ?— 
“ 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, &c.—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.”—{Life and Letters, vol. Hi., ft. /jp.) 
And yet his opinion upon this subject seems to be far 
from fixed, for elsewhere he says :— 
“In North America, in going from north to south, or from east to 
west, it is clear that the changed conditions of life have modified the 
organisms in the different regions, so that they now form distinct 
races, or even species. It is further clear that in isolated districts, 
however small, the inhabitants almost always get slightly modified, 
and how far this is due to the nature of the slightly different 
conditions to which they are exposed, and how far to mere inter 
breeding in the manner explained by Weismann, I can form no 
opinion.”—{Life a?id Letters, vol. Hi., ft. 161.) 
But interbreeding is equivalent to panmixia, and panmixia 
is equivalent to the absence of Natural Selection. What, 
then, is the opinion of Mr. Darwin on this subject? 
1. That in a limited area Natural Selection will act, or 
will tend to act, through the uniformity of the conditions. 
2. That Natural Selection will tend not to act through the 
small output of variation which there necessarily must be 
in a small area. 3. That transforming influence—not 
selection—will act in a limited area, of which the case of 
the Saturnia is held to be a proof. 4. He does not know 
whether to attribute the transmutation to transforming 
influence or to interbreeding, i.e., the absence of Natural 
Selection. 
The phenomena which we have been considering seem 
to accord with the idea of a transforming influence ; they