DARWINISM 
CHAP. 
animals and plants which live together in any one country, 
and to give some rational account of the phenomena presented 
by their distribution in different parts of the world. And, 
lastly, we may expect it to explain many difficulties and to 
harmonise many incongruities in the excessively complex 
affinities and relations of living things. All this the Darwinian 
theory undoubtedly does. It shows us how, by means of 
some of the most universal and ever-acting laws in nature, 
new species are necessarily produced, while the old species 
become extinct; and it enables us to understand how the 
continuous action of these laws during the long periods with 
which geology makes us acquainted is calculated to bring 
about those greater differences presented by the distinct 
genera, families, and orders into which all living things are 
classified by naturalists. The differences which these present 
are all of the same nature as those presented by the species of 
many large genera, but much greater in amount; and they can 
all be explained by the action of the same general laws and 
by the extinction of a larger or smaller number of intermediate 
species. Whether the distinctions between the higher groups 
termed Classes and Sub-kingdoms may be accounted for in 
the same way is a much more difficult question. The differ¬ 
ences which separate the mammals, birds, reptiles, and fishes 
from each other, though vast, yet seem of the same nature as 
those which distinguish a mouse from an elephant or a 
swallow from a goose. But the vertebrate animals, the 
mollusca, and the insects, are so radically distinct in their 
whole organisation and in the very plan of their structure, 
that objectors may not unreasonably doubt whether they can 
all have been derived from a common ancestor by means of 
the very same laws as have sufficed for the differentiation 
of the various species of birds or of reptiles. 
The Change of Opinion effected by Darwin. 
The point I wish especially to urge is this. Before 
Darwin’s work appeared, the great majority of naturalists, and 
almost without exception the whole literary and scientific 
world, held firmly to the belief that species were realities, and 
had not been derived from other species by any process 
accessible to us ; the different species of crow and of violet 
