4 
INTRODUCTION 
very potent factor in Evolution. Whether Natural Selection—even 
with such limited aid as it may have received from Sexual Selection 
and the little understood direct Influence of the Environment 1 —has 
been the sole cause at work throughout past ages in the production 
of the almost infinite variety of animals and plants, living and 
extinct—whether we can adequately explain by Natural Selection 
the first steps in the evolution of the eye, the ear, the organs of flight, 
or even of so-called Mimicry—these are questions far too large for 
discussion in these pages. 
As regards Mimicry there is just one point that should be empha¬ 
sized. Even although it may be demonstrated that some creature or 
creatures readily feed upon a certain insect, it may nevertheless be 
quite allowable to describe that insect as relatively unpalatable, if it 
can be shown that other insectivorous animals habitually, or even 
frequently, reject it. Similarly to demonstrate that butterfly A 
really is protected by its resemblance to butterfly B, it is by no 
means necessary to prove that A deceives all its enemies, or even 
always deceives one enemy in particular. The protection to the 
species may be very real if its enemies (or any of them) are occasion¬ 
ally deceived by the resemblance. 
1 The reality of the influence of the environment in the production of colour has 
been clearly proved by Prof. E. B. Poulton, F.R.S., but he explains his results as 
brought about through the nervous system, and not by the direct action of light on 
the skin—the susceptible nervous system being itself a product of natural selection. 
See Colours of Animals , Chapters viii, ix. Also Trans. Ent. Soc. Lond. 1908, p. 811 
et seq. Also Essays on Evolution, pp. 152-4. 
