NATTJBAL SELECTION. 145 



service was effected by the English naturalist, Charles Darwin, 

 who employed a mass of scientific material to found a theory of the 

 origin and mutation of species. This theory, which is closely con- 

 nected with the views of Lamark and Geoffroy and in harmony with 

 Lyell's doctrines, has received an almost universal recognition, not 

 only on account of the simplicity of its principle, but also because of 

 the objective and convincing way in which his genius expounded it. 



Darwin * starts from the principle of heredity, according to 

 which the characteristics of parents are transmitted to their off- 

 spring. But side by side with this, there is an adaptation determined 

 by the peculiar conditions of nourishment, a limited variability of 

 form, without which individuals of like descent would be identical. 

 While heredity tends to reproduce identical characteristics, individual 

 variations appear in the descendants of the same species, and in this 

 way modifications arise, which in their turn are submitted to the 

 law of heredity. Cultivated plants and domestic animals, the 

 individual forms of which vary far more than do those living in a 

 state of nature, are especially disposed to alteration ; and capability 

 of domestication is in reality nothing else than the capability of an 

 organism to siibordinate and adapt itself to altered conditions of 

 nourishment and way of life. 



The so-called artificial breeding, by which man succeeds by judicious 

 choice in cultivating in plants and animals definite properties cor- 

 responding to his requirements, depends on the interaction of heredity 

 and individual variation ; and it is probable that the numerous races 

 of domestic animals were in this way bred unconsciously by man, just 

 as in our own days large numbers of new varieties are bred by judi- 

 cious choice of the male and female parents. Similar processes are 

 also at work in natural life, calling into existence new alterations 

 and varieties. Here also we find a selection which is occasioned by 

 the struggle of organisms for existence, and may be called a natural 

 selection. All plants and animals are engaged, as Decandolle and 

 Lyell had asserted ten years previously, in a mutual struggle for 

 existence among themselves and with external conditions. 



A plant has to fight against circumstances of climate, season, and 

 soil ; and has also to compete for existence with other plants which, 

 by their superabundant increase, endanger the possibility of it> 

 preservation. Plants serve as food for animals, which themselves 

 are engaged in a mutual struggle with each other ; the carnivorous 



* Ch. Darwin. ' ; On the Origin of Species by means of Natural Selection." 

 London, 1859. 



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