1909] The Ottawa Naturalist. 89 



Isidore St. Hilaire, (1805-1861) son of Geoflfroy St. Hilaire, 

 advanced the theory that species were limited in their mutabiHty. 

 He claimed that new characters may be produced as a result of 

 two forces: 



(1) The modifying influence of new surroundings, 



(2) The conserving influences of heredity. 



Dr. W. C. Wells in 1813 was the first to apply the principle 

 of "The survival of the fittest." He based his theory on the 

 observation that no two individvials are alike and that those 

 which are best fitted to withstand the exigencies of a particular 

 country or locality are most likely to survive. In 1831 Patrick 

 Matthews applied a similar view in a book on naval timber. 



THE darwinian THEORY. 



It remained with Chas. Darwin (1809-1882), to bring 

 out a well rounded theory attempting to explain the origin 

 of species and varieties. His great work under this name was 

 inspired by an essay by Malthus on "Population" written in 

 1798. After many years of most thorough work in which he 

 collected an immense amount of evidence he crystallized his 

 views on the subject into a theory known as the "Theory of 

 Natural Selection." In a word this theory implies that favorable 

 variations are preserved while the injurious or inferior variations 

 are rejected. That is to say that in the struggle for existence 

 onlv the strongest individuals survive while the weaker succumb 

 to the various active forces of nature. This principle assumes that 

 constant variation is going on within the race and that by the 

 gradual accumulation of slight favorable variations new species 

 are formed. Darwin based his theory of natural selection largely 

 upon the results realized by man in artificially selecting from his 

 flocks and herds. He recognized that variation might be induced 

 as follows: (1) By environment. (2) By the use or disuse of 

 parts. (3) By certain inherent forces causing definite variation. 

 (4) By the tendency of variations to become co-related. (5) By re- 

 version. (6) By telegony. Two main classes of variation were 

 recognized, viz. : fluctuating variation and discontinuous varia- 

 tion. Darwin believed that fluctuating variations had been 

 utilized most bv the breeder although it is difficult to distinguish 

 between the two. According to Quetelet, Galton and others, 

 these fluctuating variations are grouped around a "mean" in 

 such a way that approximately half are below the mean and half 

 above. 



Wagner claims that variation, isolation or selection, and 

 heredity constitute the tripod of organic evolution. In other 

 words, plants are constantly changing in character, and, since 

 like tends to beget like" in plants just as in animals, the isolation 



