male through the fortunate chance of a few feathers being left
unchanged, we can distinctly trace how simple spots with a little
fulvous shading on one side may have been developed by small steps into
the wonderful ball-and-socket ornaments; and it is probable that they
were actually thus developed.
Everyone who admits the principle of evolution, and yet feels great
difficulty in admitting that female mammals, birds, reptiles, and fish,
could have acquired the high taste implied by the beauty of the males,
and which generally coincides with our own standard, should reflect
that the nerve-cells of the brain in the highest as well as in the
lowest members of the Vertebrate series, are derived from those of the
common progenitor of this great Kingdom. For we can thus see how it has
come to pass that certain mental faculties, in various and widely
distinct groups of animals, have been developed in nearly the same
manner and to nearly the same degree.
The reader who has taken the trouble to go through the several chapters
devoted to sexual selection, will be able to judge how far the
conclusions at which I have arrived are supported by sufficient
evidence. If he accepts these conclusions he may, I think, safely
extend them to mankind; but it would be superfluous here to repeat what
I have so lately said on the manner in which sexual selection
apparently has acted on man, both on the male and female side, causing
the two sexes to differ in body and mind, and the several races to
differ from each other in various characters, as well as from their
ancient and lowly-organised progenitors.
He who admits the principle of sexual selection will be led to the
remarkable conclusion that the nervous system not only regulates most
of the existing functions of the body, but has indirectly influenced
the progressive development of various bodily structures and of certain
mental qualities. Courage, pugnacity, perseverance, strength and size
of body, weapons of all kinds, musical organs, both vocal and
instrumental, bright colours and ornamental appendages, have all been
indirectly gained by the one sex or the other, through the exertion of
choice, the influence of love and jealousy, and the appreciation of the
beautiful in sound, colour or form; and these powers of the mind
manifestly depend on the development of the brain.
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