ORIGIN OF ORGANIC FORMS 301 



of the common origin of organic beings (and therefore, 

 as we have already seen, of the wider problem still, of 

 the cause of their perfection) is bound up with the 

 problem of the variability, or, speaking more generally, 

 of the origin of species. That is how Darwin's book, 

 which caused a revolution in science, came to bear such 

 a dry and technical title. 



Is it really true, as was steadily affirmed by a majority 

 of naturalists, that species are variable ? In the first 

 place we know that no two exactly similar forms exist in 

 nature : plants grown from seeds of one and the same fruit 

 vary one from another. Hence entire similarity is out 

 of the question, and, as a matter of fact, no one has ever 

 suggested it. Moreover, we know perfectly well that 

 even within the limits of a species there may be narrower 

 groups of beings still more closely resembling one another. 

 Thus the species, serving as a unit for groups of a higher 

 order, in its turn breaks up into units of a lower order. 

 Everybody knows how different are the races of dogs, 

 how diverse the kinds of wheat, how numerous the 

 variety of flowers appearing year by year in gardeners' 

 catalogues. Where is the famous immutability of 

 species ? The exponents of this theory have a ready 

 answer. They say : ' Within the limits of species 

 variation may certainly occur, but the range of these 

 variations is limited ; the degree of difference between 

 the varieties can never be as great as that between 

 species ' : in other words, new species cannot be formed 

 in the same way as new varieties. Therefore the 

 question as to the immutability of species resolves 

 itself into the question of limitation in variation, or 

 rather into the significance of variations. After such a 

 categorical affirmation of the difference between a 

 species and a variety, those who uphold the immutability 

 of species might be expected to give an exact defini- 

 tion of both terms, and to provide a criterion whereby 

 we may know when we are dealing with two varieties 



