Organic Evolution. 203 



colours are suggestive of a nasty taste. The insect-eating 

 birds associate nastiness especially with certain markings 

 and coloration " the tawny Danais, the barred Heliconias, 

 the blue-black JSuplceas, and the fibrous Acr&as;" and 

 this is proved by the fact that sweet insects mimicking 

 these particular forms are thereby protected. 



So, too, with recognition-marks. If the bird or the 

 mammal have not sufficient perceptive powers to distinguish 

 between the often not very different recognition-marks, of 

 what service can they be ? 



Keeognition-marks and mimicry seem, therefore, to show 

 that in the former case many animals, and in the latter 

 the insect-eating birds, mammals, lizards, and other 

 animals concerned, have considerable powers of perception 

 and association. 



Among other associations are those which are at the 

 base of what I have termed preferential mating. We must 

 remember how deeply ingrained in the animal nature is 

 the mating instinct. We may find it difficult to distinguish 

 closely allied species. But the individuals of that species 

 are led to mate together by an impelling instinct that is so 

 well known as to elicit no surprise. Instinct though it be, 

 however, the mating individuals must recognize each other 

 in some way. The impulse that draws them together must 

 act through perceptual agency. It is not surprising, there- 

 fore, to find, when we come to the higher animals, that, 

 built upon this basis, there are well-marked mating pre- 

 ferences. And this, as we have before pointed out, follow- 

 ing Wallace, is an efficient factor in segregation. Let us, 

 however, hear Mr. Wallace himself in the matter. 



There is, he says,* " a very powerful cause of isolation 

 in the mental nature the likes and dislikes of animals ; 

 and to this is probably due the fact of the rarity of hybrids 

 in a state of nature. The differently coloured herds of 

 cattle in the Falkland Islands, each of which keeps 

 separate, have been already mentioned. Similar facts 

 occur, however, among our domestic animals, and are 



* " Darwinism," p. 172. 



