12 THE CLASSIFICATION OF BIRDS 



many unexplained, and we are driven to the unsatisfactory method 

 of argument by analogy. We are forced to assume that it is 

 merely our ignorance that prevents us from recognising the satis- 

 factory nature of the explanation. It may be that many birds 

 have changed their environment, possibly several times ; that in 

 many cases the environments themselves have changed, either 

 temporarily or permanently; and that each change has left its 

 mark upon the species, until the characters have been so entangled 

 together that the attempt to unravel the mystery of their genea- 

 logy is almost hopeless. 



When Darwin had convinced the scientific world that the 

 theory of Evolution was a reasonable hypothesis, and not the wild 

 dream that nearly all learned men at that time supposed it to be, 

 it was assumed that a natural classification of animals and plants 

 was a problem of comparatively easy solution. It was taken for 

 granted that the key had at length been discovered which was to 

 unlock the mysteries of affinity and analogy. All that was neces- 

 sary to produce a natural classification was to arrange animals and 

 plants according to their genetic affinities. It was supposed that 

 an examination of fossil animals and plants would throw a flood 

 of light upon the relationship of recent organisms, and that the 

 descent of important characters could be easily .traced back to 

 their origin from common ancestors. So far as Ornithology is 

 concerned, the result has been very disappointing. The geological 

 record has been found to be extremely imperfect; Very few 

 species have been found in a fossil state. In very few cases have 

 any but osteological characters been preserved, and even these are 

 for the most part very fragmentary. It is of course obvious that 

 if all birds have descended from common ancestors, and if we had 

 access to examples of all the intermediate forms which have con- 

 nected existing birds with their common ancestors, no classification 

 would be possible, for every species would be connected with every 

 other species by an unbroken series of intermediate forms gradu- 

 ally and insensibly leading from one to the other. It is of course 

 a subject of profound scientific interest to discover any trace in 

 the geological past of the missing links that fill up the gaps 

 between the various families of existing birds, but so far the 

 fragments of knowledge that have been acquired. by a study of 

 Paleontology have thrown little or no light upon the vexed ques- 

 tion of the classification of Birds ; and for the present at least it 

 seems to be impossible to include fossil birds, except those of very 



