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NATURAL
SELECTION AND TROPICAL NATURE ESSAYS ON DESCRIPTIVE AND THEORETICAL BIOLOGY BY ALFRED RUSSEL WALLACE IX. THE LIMITS OF NATURAL SELECTION AS APPLIED TO MAN THROUGHOUT this volume I have
endeavoured to show that the known laws of variation, multiplication, and heredity,
resulting in a "struggle for existence" and the "survival of the
fittest," have probably sufficed to produce all the varieties of structure,
all the wonderful adaptations, all the beauty of form and of colour, that we see
in the animal and vegetable kingdoms. To the best of my ability I have answered
the most obvious and the most often repeated objections, to this theory, and have,
I hope, added to its general strength, by showing how color--one of the strongholds
of the advocates of special creation--may be, in almost all its modifications,
accounted for by the combined influence of sexual selection and the need of protection.1
I have also endeavored to show how the same power which has modified animals has
acted on man; and have, I believe, proved that, as soon as the human intellect
became developed above a certain low stage, man's body would cease to be materially
affected by natural selection, because the development of his mental faculties
would render important modifications of its form and structure unnecessary. It
will, therefore, probably excite some surprise among my readers to find that
I do not consider that all nature can be explained on the principles of which
I am so ardent an advocate; and that I am now myself going to state objections,
and to place limits, to the power of natural selection. I believe, however, that
there are such
limits; and that just as surely as we can trace the action of natural laws in the development of organic forms, and can clearly conceive that fuller knowledge would enable us to follow step by step the whole process of that development, so surely can we trace the action of some unknown higher law, beyond and independent of all those laws of which we have any knowledge. We can trace this action more or less distinctly in many phenomena, the two most important of which are--the origin of sensation or consciousness, and the development, of man from the lower animals. I shall first consider the latter difficulty as more immediately connected with the subjects discussed in this volume. What Natural Selection can Not do In considering the question of the development of man by known natural laws, we must ever bear in mind the first principle of natural selection, no less than of the general theory of evolution, that all changes of form or structure, all increase in the size of an organ or in its complexity, all greater specialisation or physiological division of labour, can only be brought about; in as much as it is for the good of the being so modified. Mr. Darwin himself has taken care to impress upon us that natural selection has no power to produce absolute perfection, but only relative perfection,--no power to advance any being much beyond his fellow beings, but only just so much beyond them as to enable it to survive them in the struggle for existence. Still less has it any power to produce modifications which are in any degree injurious to its possessor, and Mr. Darwin frequently uses the strong expression, that a single case of this kind would be fatal to his theory. If, therefore, we find in man any characters, which all the evidence we can obtain goes to show would have been actually injurious to him on their first appearance, they could not possibly have been produced by natural selection. Neither could any specially developed organ have been so produced if it had been merely useless to him, or if its use were not proportionate to its degree of development. Such cases as these would prove that some other law, or some other power, than natural selection had been at work. But if, further, we could see that these very modifications, though hurtful or |
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