ry occasions of life that any slight
superiority in one part can be at once utilised; while the moment any
want of balance occurs, variations in the insufficiently developed parts
will be selected to bring back the harmony of the whole organisation.
The fact that, in all domestic animals, variations do occur, rendering
them swifter or stronger, larger or smaller, stouter or slenderer, and
that such variations can be separately selected and accumulated for
man's purposes, is sufficient to render it certain that similar or even
greater changes may be effected by natural selection, which, as Darwin
well remarks, "acts on every internal organ, on every shade of
constitututional difference, on the whole machinery of life." The
difficulty as to co-adaptation of parts by variation and natural
selection appears to me, therefore, to be a wholly imaginary difficulty
which has no place whatever in the operations of nature.

_Direct Action of the Environment._

Mr. Spencer's last objection to the wide scope given by Darwinians to
the agency of natural selection is, that organisms are acted upon by the
environment, which produces in them definite changes, and that these
changes in the individual are transmitted by inheritance, and thus
become increased in successive generations. That such changes are
produced in the individual there is ample evidence, but that they are
inherited independently of any form of selection or of reversion is
exceedingly doubtful, and Darwin nowhere expresses himself as satisfied
with the evidence. The two very strongest cases he mentions are the
twenty-nine species of American trees which all differed in a
corresponding way from their nearest European allies; and the American
maize which became changed after three generations in Europe. But in the
case of the trees the differences alleged may be partly due to
correlation with constitutional peculiarities dependent on climate,
especially as regards the deeper tint of the fading leaves and the
smaller size of the buds and seeds in America than in Europe; while the
less deeply toothed or serrated leaves in the American species are, in
our present complete ignorance of the causes and uses of serration,
quite as likely to be due to some form of adaptation as to any direct
action of the climate. Again, we are not told how many of the allied
species do not vary in this particular manner, and this is certainly an
important factor in any conclusion we may form