WHAT IS EVOLUTION? 43 



stantly in a narrow circle, and constantly use such 

 formulae as we may well suppose, instead of argu 

 ment 



We may take as an example from Wallace the 

 history of the evolution of the water-ouzel or dipper. 

 It may serve as an example of the questions which 

 are raised by the Darwinian evolution, and which, if 

 they have no other advantage, tend to promote the 

 minute observation of nature, of which Wallace s book 

 shows many interesting examples. It serves, at the 

 same time, to illustrate that peculiar style of reasoning 

 in a circle which is characteristic of this school of 

 thought. I have chosen this special illustration from 

 Wallace because it is one in which the idea of adapta 

 tion to fill a vacant space an idea as much Lamarckian 

 as Darwinian is introduced. 



An excellent example of how a limited group of species 

 has been able to maintain itself by adaptation to one of 

 these vacant places in nature is afforded by the curious 

 little birds called dippers or water-ouzels, forming the genus 

 Cinclus of the family Cindidcz of naturalists. These birds are 

 something like small thrushes, with very short wings and 

 tail and very dense plumage. They frequent, exclusively, 

 mountain torrents in the northern hemisphere, and obtain 

 their food entirely in the water, consisting, as it does, of 

 water-beetles, caddis-worms, and other insect larvae, as well 

 as numerous small fresh-water shells. These birds, although 

 not far removed in structure from thrushes and wrens, have 

 the extraordinary power of flying under water ; for such, 

 according to the best observers, is their process of diving 

 in search of their prey, their dense and somewhat fibrous 



