Lefevre — The Advance of Zoology in the Nineteenth Century. 91 



the beginning on the side of Darwin, and for some years a 

 fierce battle was waged between the advocates and opponents 

 of Natural Selection. Darwin took little part in these con- 

 troversies himself, and it was largely due to the spirited efforts 

 of a handful of loyal supporters, notably of Huxley in En- 

 gland and Haeckel in Germany, that the brilliant victory for 

 the descent-theory was won. Although ideas of organic evo- 

 lution had been expressed at intervals from the time of the 

 Greeks, and in a few instances a cause of the transmutation 

 had been offered, as in Lamarck's system, Darwin was the 

 first to propose a reasonable explanation of the origin of 

 species based upon observed fact. No scientific work of the 

 century has attracted so much attention, not only in the 

 zoological, but in the entire educated world; and at the 

 present time our whole scientific thought is so thoroughly 

 permeated with the idea of the descent-theory, that there is 

 no department of knowledge which has not felt its far-reaching 

 influence. 



So familiar is the theory of Natural Selection to every one 

 that the briefest outline will suffice. The over-production of 

 individuals leads to a fierce struggle for existence among all 

 living things, a struggle which is both active and passive, 

 occurring not only between organisms but between the organ- 

 ism and its environment, a struggle which is to result either 

 in the destruction of the individual or its survival. Those 

 individuals survive which can, and it is the fittest, or those 

 which are best suited to withstand the ceaseless life- struggle, 

 that will constitute the favored. Upon Darwin's theory the 

 origin of species is accounted for by the hereditary transmis- 

 sion of "fortuitous" congenital variations which are useful 

 to the organism by giving it an advantage in the struggle for 

 existence and thus determining whether the organism is to 

 survive to produce offspring or to perish without leaving off- 

 spring. In order that the character should be selected, it 

 must be useful, must be at some time a life-preserving char- 

 acter, and the fundamental principle underlying the process 

 of Natural Selection is that of utility. It is a matter of com- 

 mon observation that no two individual animals or plants of 

 the same species, even those derived from the same parents, 



