534 THE POPULAR SCIENCE MONTHLY 



extreme changes in the climate of tropical lowlands during the Glacial 

 Period on which Darwin founded his interpretation. The causes and 

 influence of the Glacial Epoch are discussed in an exposition of Croll's 

 theory. In this connection may be mentioned one of Wallace's original 

 geological contributions, in the article " Glacial Erosions of Lake 

 Basins," published in 1893, namely, his theory of glacial erosion as a 

 means of explaining the origin of valley lakes of glaciated countries. 



The original trend of Wallace's thought as to the ascent of man is 

 first shown in the three anthropological essays of 1864, 1869 and 1870, 

 which were subsequently collected in the volume " Contributions to the 

 Theory of Natural Selection." This work, published in 1871, includes 

 all his original essays from 1855' to 1869 on selection, on color and 

 human evolution, which foreshadow the later development of his specu- 

 lative philosophy. 



A suggestive anthropological contribution is the article entitled " The 

 Expressiveness of Speech or Mouth Gesture as a Factor in the Origin 

 of Language," in which is developed the theory of the origin of language 

 in connection with the motions of the lips, jaws and tongue. With Wal- 

 lace also arose the now widely accepted belief that the Australian 

 aborigines constitute a low and perhaps primitive type of the Caucasian 

 race. 



In the article of 1864, "The Development of Human Eaces under 

 the Law of Natural Selection," Wallace first advanced the hypothesis 

 which has since proved to be untenable that so soon as man learned to 

 use fire and make tools, to grow food, to domesticate animals, to use 

 clothing and build houses, the action of natural selection was diverted 

 from his body to his mind, and thenceforth his physical form remained 

 stable, while his mental faculties improved. His subsequent papers on 

 human evolution, " The Limits of Natural Selection as Applied to Man " 

 of 1869, " On Instinct in Man and Animals " of 1871, mark the gradual 

 divergence of his views from those of Darwin, for in his opinion natural 

 selection is believed to be inadequate to account for several of the phys- 

 ical as well as psychical characteristics of man, for example his soft, 

 sensitive skin, his speech, his color sense, his mathematical, musical and 

 moral attributes. He concluded : 



The inference I would draw from this class of phenomena is that a superior 

 intelligence has guided the development of man in a definite direction, and for a 

 special purpose, just as man guides the development of many animal and veg- 

 etable forms. 



It is also prophetic of his later indictments of the so-called civiliza- 

 tion of our times that we find at the end of the closing pages of " The 

 Malay Archipelago" the first statement of the feeling which so many 

 travellers have experienced from a comparison of the natural and so- 

 called civilized condition of man that " social evolution from barbarism 



