This, too, had a further advantage
in that, after discussing variations and the effects of artificial
selection, it was possible at once to explain how Natural Selection
acts.
The subjects treated with novelty and interest in their important
bearings on the theory of Natural Selection were: (1) A proof that all
_specific_ characters are (or once have been) either useful in
themselves or correlated with useful characters (Chap. VI.); (2) a proof
that Natural Selection can, in certain cases, increase the sterility of
crosses (Chap. VII.); (3) a fuller discussion of the colour relations of
animals, with additional facts and arguments on the origin of sexual
differences of colour (Chaps. VIII.-X.); (4) an attempted solution of
the difficulty presented by the occurrence of both very simple and
complex modes of securing the cross-fertilisation of plants (Chap. XI.);
(5) some fresh facts and arguments on the wind-carriage of seeds, and
its bearing on the wide dispersal of many arctic and alpine plants
(Chap. XII.); (6) some new illustrations of the non-heredity of acquired
characters, and a proof that the effects of use and disuse, even if
inherited, must be overpowered by Natural Selection (Chap. XIV.); and
(7) a new argument as to the nature and origin of the moral and
intellectual faculties of man (Chap. XV.).
"Although I maintain, and even enforce," wrote Wallace, "my differences
from some of Darwin's views, my whole work tends forcibly to illustrate
the overwhelming importance of Natural Selection over all other agencies
in the production of new species.
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