118 THE PRESIDENTS ADDRESS. 
Species,”’ illustrated by highly ingenious analogies, and not only sug- 
gesting clearer definitions, but also supplying some very compre- 
hensive bases of thought. The problem, however, is not one of easy 
solution. After various oscillations in the phases of expressed opin- 
ion, Professor Baden Powell, has boldly taken up the enquiry in the 
whole comprehensive bearings of “ The Philosophy of Creation,” and 
in this work, among other profound questions, he gives special im- 
portance to that of the immutability or transmutation of species, as 
one of the most significant in relation to all the final deductions on 
which the disclosures of geology, and the scientific foundations of 
cosmo-theology, compel us to render our verdict anew. 
Still more, recently an eminent English Naturalist: Charles 
Darwin, has in his elaborate introductory treatise: “On the origin 
of species by means of natural selection,” carried to undisguised con- 
clusions, and with systematic details of evidence and results, some of 
those opinions which Professor Powell has only left to be surmised. 
According to Mr. Darwin, the essential differences of genera are only 
the product of the same powers of nature through a greatly protracted 
epoch, which within a less prolonged period had sufficed to produce 
species ; and under our own limited observation are seen to give rise 
to permanent varieties in animals and plants. From observation of 
phenomena occurring within our own cognizance he has arrived at the. 
conclusion that there is in reality no essential distinction between 
individual differences, varieties, and species. The well-marked variety 
is an incipient species ; and by the operation of various simple physi- 
cal causes, and comparatively slight organic changes, producing a 
tendency towards increase in one direction of variation, and arrest- 
ment, and ultimate extinction in another, that law of natural selection, 
as Darwin terms it, results, which leads to his “ preservation of fa- 
voured races in the struggle for life.’ He thus establishes, as he 
conceives, a principle in nature, akin to that which man consciously 
sets in operation, when he effects changes on domesticated animals 
and on plants, by altered conditions of life, and then perpetuates such 
as he selects by preference for his ownuse. The element of time— 
so limited in man’s operations,—is for practical purposes unlimited 
in relation to the operation of natural causes on the development of 
variations in organic being in diverse directions; and as the great 
physical changes to which geology bears witness, supply all the means 
requisite for producing individual variations on a scale immensely ex- 
