The Descent of Man

stage in the process of modification, all the individuals
which were in any way better fitted
for their conditions of life, though in different
degrees, would have survived in greater numbers
than the less well-fitted. The process
would have been like that followed by man,
when he does not intentionally select particular
individuals, but breeds from all the superior
individuals, and neglects the inferior. He thus
slowly but surely modifies his stock, and unconsciously
forms a new strain. So with respect
to modifications acquired independently of
selection, and due to variations arising from the
nature of the organism and the action of the
surrounding conditions, or from changed
habits of life, no single pair will have been modified
much more than the other pairs inhabiting
the same country, for all will have been
continually blended through free intercrossing.
By considering the embryological structure of
man,—the homologies which he presents with