ALFRED RUSSEL WALLACE 533 



We find, then, that neither the general influence of solar light and heat, nor 

 the special action of variously tinted rays, are adequate causes for the wonderful 

 variety, intensity and complexity of the colors that everywhere meet us in the 

 animal and vegetable worlds. Let us, therefore, take a wider view of these colors, 

 grouping them into classes determined by what we know of their actual uses or 

 special relations to the habits of their possessors. This, which may be termed 

 the functional and biological classification of the colors of living organisms, seems 

 to be best expressed by a division into five groups, as follows : 

 f 1. Protective colors. 



! 2 Warning colors i a ' 0f creatures specially protected. 

 Animals. ^ & \ o. Of defenceless creatures, mimicking a. 



j 3. Sexual colors. 



[_ 4. Typical colors. 



Plants. 5. Attractive colors. 



Twelve years later he devoted four chapters of his " Darwinism " to 

 the colors of animals and plants, still maintaining the hypotheses of 

 utilit} r , of spontaneous variation and of selection. 



The study of geographic distribution of animals also sprang from the 

 inspiration of the Malayan journey and from the suggestiveness of the 

 eleventh and twelfth chapters of "The Origin of Species" which Wal- 

 lace determined to work out in an exhaustive manner. Following the 

 preliminary treatises of Buffon, of Cuvier and Forbes, and the early 

 regional classification of Sclater, Wallace takes rank as the founder of 

 the science of zoogeography in his two great works, " The Geographical 

 Distribution of Animals" of 1876, and "Island Life" of 1881, the 

 latter volume following the first as the result of four years of additional 

 thought and research. His early observations on insular distribution 

 were sketched out in his article of 1860, " The Zoological Geography of 

 the Malayan Archipelago." 



Here is his discovery of the Bali-Lombok boundary line between the 

 Indian and the Australian zoological regions which has since been 

 generally known by his name. 



In these fundamental geologic and geographic works Wallace ap- 

 pears as a disciple of Lyell in uniformitarianism, and a follower of Dana 

 as regards the stabilit} r and permanence of continental and oceanic areas, 

 for which doctrine he advances much original evidence. He taxes his 

 ingenuity to discover every possible means of dispersal of animals and 

 plants other than those which would be afforded by hypothetical land 

 connections; he considers every possible cause of extinction other than 

 those which are sudden or cataclysmal. 



The "Island Life" is in itself a great contribution to zoology and 

 zoogeography, the starting point of all modern discussion of insular 

 faunas and floras. His conservative theory of dispersal is applied in an 

 original way to explain the arctic element in the mountain regions of the 

 tropics, as opposed to the low-temperature theory of tropical lowlands 

 during the Glacial Period; his explanation is founded on known facts 

 as to the dispersal and distribution of plants, and does not require the 



