Animals of this kind will not usually receive a
stranger into their midst. While they keep together they are generally
safe from attack, but a solitary straggler becomes an easy prey to the
enemy; it is, therefore, of the highest importance that, in such a case,
the wanderer should have every facility for discovering its companions
with certainty at any distance within the range of vision.
Some means of easy recognition must be of vital importance to the young
and inexperienced of each flock, and it also enables the sexes to
recognise their kind and thus avoid the evils of infertile crosses; and
I am inclined to believe that its necessity has had a more widespread
influence in determining the diversities of animal coloration than any
other cause whatever. To it may probably be imputed the singular fact
that, whereas bilateral symmetry of coloration is very frequently lost
among domesticated animals, it almost universally prevails in a state of
nature; for if the two sides of an animal were unlike, and the diversity
of coloration among domestic animals occurred in a wild state, easy
recognition would be impossible among numerous closely allied forms.
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