126 AFRICAN GAME ANIMALS 



past. Mr. Pycraft (unlike Professor Poulton, and especially 

 unlike Mr. Thayer) fully recognizes, and insists upon, the 

 fact that there is no warrant for believing that these pat- 

 terns are due to existing factors of selection or to the action 

 of selective forces now at work; he explicitly states that 

 they are due only to the action of these transforming factors 

 on the generations of a remote past — although we believe 

 he lays unwarranted stress upon their having survived only 

 to the degree that they still continue to be adaptatively 

 perfect and efficient, for we believe that they no longer 

 have survival value. As to whether they formerly were 

 survival factors, we are in doubt; for their elimination, even 

 where the environment seems substantially unchanged, cer- 

 tainly warrants such doubt. Spencer Trotter, in his studies 

 in the Auk and the Journal of the Academy of Natural 

 Sciences, of Philadelphia, dwells on the evanescent nature 

 of what we speak of as "faunas," pointing out that *'a 

 fauna" is merely an expression of the temporary adjust- 

 ment of any group of animals to given conditions of en- 

 vironment — vegetation, moisture, temperature, and many 

 other factors combining to determine or condition the en- 

 vironment — so that the species which embody a fauna are 

 mobile elements, not hard-and-fast fixtures in their en- 

 vironment, their present phase of distribution being a se- 

 quence to their past history. 



A glance at the animals of desert, or arid and semlarid 

 regions, is interesting from this standpoint. The general 

 color tone of the animals of arid regions is pallid and neu- 

 tral, just as the general color tone of arctic animals is white 

 and that of animals of temperate humid regions, such as 

 the neighborhood of Puget Sound, is dark. There are, of 



