n still more clearly recognizes these causes of change in
organization. A chapter is devoted to the subject. After premising that
"the direct action of the conditions of life, whether leading to
definite or indefinite results, is a totally distinct consideration from
the effects of natural selection;" he goes on to say that changed
conditions of life "have acted so definitely and powerfully on the
organisation of our domesticated productions, that they have sufficed
to form new sub-varieties or races, without the aid of selection by man
or of natural selection." Of his examples here are two.

"I have given in detail in the ninth chapter the most remarkable
case known to me, namely, that in Germany several varieties of
maize brought from the hotter parts of America were transformed in
the course of only two or three generations." (Vol. ii, p. 277.)
[And in this ninth chapter concerning these and other such
instances he says "some of the foregoing differences would
certainly be considered of specific value with plants in a state of
nature." (Vol. i, p. 321.)] "Mr. Meehan, in a remarkable paper,
compares twenty-nine kinds of American trees, belonging to various
orders, with their nearest European allies, all grown in close
proximity in the same garden and under as nearly as possible the
same conditions." And then enumerating six traits in which the
American forms all of them differ in like ways from their allied
European forms, Mr. Darwin thinks there is no choice but to
conclude that these "have been definitely caused by the
long-continued action of the different climate of the two
continents on the trees." (Vol. ii, pp. 281-2.)

But the fact we have to note is that while Mr. Darwin thus took account
of special effects due to special amounts and combinations of agencies
in the environment, he did not take account of the far more important
effects due to the general and constant operation of these agencies.[43]
If a difference between the quantities of a force which acts on two
organisms, otherwise alike and otherwise similarly conditioned, produces
some difference between them; then, by implication, this force produces
in both of them effects which they show in common. The inequality
between two things cannot have a value unless the things themselves have
values. Similarly if, in two cases, some unlikeness of proportion among
the surroun