DEFINITION OF SPECIES AND VARIETIES. 407 



origin. Varieties owe their origin to soil, exposure, and other causes, 

 and have a constant tendency to return to their original type. They 

 are rarely propagated by seed, but can be perpetuated by cuttings and 

 grafts. By cultivation, as well as by natural causes, permanent varie- 

 ties or races are produced, the seeds of which give rise to individuals, 

 varying much from the original specific type. Such races are kept up 

 entirely by the art of the gardener, and may be illustrated in the case 

 of the Cereal grains, and of culinary vegetables, such as Cabbages, 

 Cauliflower, Brocoli, Turnips, Eadishes, Peas. It is only after a series 

 of years that these permanent varieties have been established, and 

 there is still a tendency in their seeds, when sown in poor soil and 

 neglected, to produce the original wild form. Permanent varieties in 

 the animal kingdom may be illustrated by the different races of 

 mankind. 



Such are the definitions of species, varieties, and races, which 

 were generally adopted by all naturalists. But of late years theories 

 have been propounded in regard to the origin of species which are not 

 in accordance with those views, and which have given rise to new 

 definitions, founded on the supposed derivation of species from others 

 previously existing. 



The tendency to variation which exists among the descendants of 

 the same original is not considered as being restrained within fixed 

 limits, but, after the lapse of long periods of time, and under the in- 

 fluence of varying external conditions, the descendants from a common 

 stock may exhibit the differences which characterise distinct species. 

 At the present time aggregates of individuals are seen, forming species. 

 These are supposed by some to have originated from pre-existing spe- 

 cies by derivation, and these again from others, and so on, till at last 

 we come to a very few primordial forms (perhaps only one). On this 

 supposition it is necessary to account for the various modifications 

 which these primordial forms have undergone in the production of the 

 present species of the globe. According to Darwin, these primordial 

 forms had a tendency to variations in structure, some of which were 

 favourable, and others unfavourable, for 'the continuance and develop- 

 ment of the species. There would then be a struggle for eJxistence, 

 and, by a method which he calls natural selection, the fittest would 

 be preserved, while the weakest would be destroyed. He therefore 

 does not look upon species as fixed and unchangeable, but as trans- 

 ition forms. Species would thus from time to time be formed, fitted 

 for the circumstances in which they were placed. This hypothesis 

 proposes to explain the various phenomena connected with the evolution 

 of species. It does not look upon each species as a direct individual 

 creation, but as produced from previous forms by a law of selection. 

 This law, however, must indicate the acting of a Creator who knows 

 the end from the beginning, and overrules all things for his own 



