RECOGNITION-MARKS 159 



to be noticed was, that these bands were only seen during 

 flight, the white markings being quite invisible when the 

 birds were at rest The importance of this fact I did not 

 see till many years later, when, in connection with other 

 similar facts, it gave a clue to their meaning and purpose. 



Now that we have learnt how rapid are the powers of 

 increase of all animals, and the extreme severity of the 

 process by which the population is kept down to a nearly 

 fixed amount by the annual destruction of all the less adapted ; 

 and further, when we know how all the higher animals roam 

 about in search of their daily food, we are able to understand 

 how vitally important it is for all such animals to be able 

 to recognise their own species from all others without fail 

 and at considerable distances. This is essential for several 

 reasons. The young and half-grown, if they have strayed 

 away from the flock or herd, need to rejoin them as soon as 

 possible ; the two sexes of the same species require to know 

 each other in the same way by unfailing marks whether they 

 are approaching from behind or from the front ; while the 

 separate portions of flocks divided by the sudden attack of 

 some enemy need to come together again as soon as possible. 

 But there is a still more important use of these distinctive 

 markings, since they are almost if not quite essential to the 

 production of new species by adaptation to change of condi- 

 tions, as will be shown later on. 



I first gave a somewhat full account of this class of 

 markings, with several characteristic illustrations, in my 

 Darwinism, in 1889; but I had briefly treated the subject 

 in my lecture on the Colours of Animals given at many 

 places in the United States and Canada in 1886-87, and in 

 England in 1888. No doubt some of the facts had been 

 noted by other writers, but I think I was the first to claim 

 for it a high place among the factors concerned in animal 

 svolution. The clearest and most picturesque illustration of 

 the subject I have seen is in a very short article by 

 Mr. E. Seton Thompson in the American periodical The 

 Auk for October 1897, from which I will quote the most 

 mportant passage : — 



" The common jack-rabbit x when squatting under a sage-bush 



1 This appears to be the common grey hare (Lepus americanus). 



