VIII 
ORIGIN AND USES OF COLOUR IN ANIMALS 
217 
by some change in the colour of the eggs, or in the structure 
or position of the nest, or by the increased care which the 
parents bestow upon the eggs. In this way the various 
divergences which now so often puzzle us may have arisen. 
Colour as a Means of Recognition. 
If avc consider the habits and life histories of those animals 
which are more or less gregarious, comprising a large pro¬ 
portion of the herbivora, some carnivora, and a considerable 
number of all orders of birds, Ave shall see that a means of 
ready recognition of its own kind, at a distance or during 
rapid motion, in the dusk of twilight or in partial cover, 
must be of the greatest advantage and often lead to the pre¬ 
servation of life. Animals of this kind Avill not usually 
receive a stranger into their midst. AYhile 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 Avith cer¬ 
tainty at any distance Avithin the range of vision. 
Some means of easy recognition must be of vital im¬ 
portance 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 deter¬ 
mining the diversities of animal coloration than any other 
cause Avhatever. To it may probably be imputed the singular 
fact that, whereas bilateral symmetry of coloration is very 
frequently lost among domesticated animals, it almost uni¬ 
versally prevails in a state of nature; for if the tAvo sides of 
an animal Avere unlike, and the diversity of coloration among 
domestic animals occurred in a Avild state, easy recognition 
Avould be impossible among numerous closely allied forms . 1 
1 Professor Wm. H. Brewer of Yale College has shown that the white 
marks or the spots of domesticated animals are rarely symmetrical, but have 
a tendency to appear more frequently on the left side. This is the case with 
horses, cattle, dogs, and swine. Among wild animals the skunk varies con¬ 
siderably in the amount of white on the body, and this too was found to be 
usually greatest on the left side. A close examination of numerous striped or 
spotted species, as tigers, leopards, jaguars, zebras, etc., showed that the 
bilateral symmetry was not exact, although the general effect of the two sides 
