The Making of Species 
the herd, it will not be to their advantage to 
follow the line it has taken. Moreover, being at 
the rear of the flock, it is not in a good position 
to take the lead, and its pursuer is likely to see 
the danger signal before its friends do. It would 
thus seem that ‘‘danger signals,” while possibly 
sometimes of service to their possessors, are on 
the whole ornaments which might profitably be 
dispensed with. Natural selection can scarcely 
be charged with the production of a character of 
such doubtful utility to the organism. 
Moreover, flourishing species of many 
gregarious animals do not possess any “signal 
flag of danger,” while, on the other hand, a great 
many solitary species display markings that 
render them very conspicuous when in motion. 
Take the case of the famous Indian Paddy Bird 
(Ardeola grayit). This, when at rest, is coloured 
so as to be very difficult to distinguish from its 
surroundings, but flight transforms it, for it then 
displays its milk-white pinions, which would 
make a perfect danger signal, if only it were not 
peculiarly solitary in its habits. Its gregarious 
brethren, the Cattle Egrets (Bubulcus coromandus), 
on the other hand, display no danger signal. 
That these recognition marks prevent the 
intercrossing of allied species and the production 
of infertile hybrids appears to be pure fiction. 
As we have already shown, hybrids between 
allied species are by no means always infertile. 
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