REVIEWS—ON THE ORIGIN OF SPECIES. 393 
tions. The truest notion of a species may perhaps be that of a group of 
developmental tendencies, fixed in the nature of things and only liable 
to modification by external causes within certain limits. Since those 
differences of plan or degree of development which mark genera, 
tribes and sub-kingdoms are without doubt at least as constant as 
those which distinguish species, it follows that these larger groups are 
natural and real associations of objects as much as species themselves, 
and that in determining them we find out, and invent names to express, 
something existing, and it is a great mistake to represent classification 
as a mere human contrivance of which there may be many varieties 
equally well founded. A classification which may serve some purposes 
may be founded upon any observed resemblances and differences 
amongst objects; but a true natural classification is the interpretation 
of the great plan of the Creator, expressing real affinities amongst 
organised beings, and pointing out their natural relationships whether 
direct or analogical, that is, whether consisting in conformity to a 
common type, or in a correspondent position as to mode of develop- 
ment and plan of life in respect to different types. 
The believers in the transmutation of species will naturally enough 
regard the case of different organisms, resembling each other in many 
important particulars, and approaching each other more or less nearly; 
as favouring their notion of a common origin of all organic structures, 
and as illustrating different stages of progress or the influence of dif- 
ferent circumstances, but the facts are equally accounted for by ad- 
mitting a certain plan of creation. They are in truth much better 
accounted for, since the regularity with which we may generally 
observe each type to display an equal number of analogous variations, 
affords proof of a great plan running throughout nature, and excludes 
the idea of the differences of species depending on such influences as 
incidental special’ development in one of the offspring of a creature, 
giving that one advantages in the struggle for existence which are 
transmitted to its descendants. 
We deduce from these considerations that it is not the business of 
the philosophical inquirer to form some theory respecting the origin 
of the various species of organised beings, unless he has first observed 
in them such signs of fluctuation and of being modified by causes, of 
which he can estimate the operation, as to turn his thoughts in that 
direction. So long as species are regarded by him as fixed and con- 
stant forms, he is not as a naturalist concerned with their origin, but 
Vou. VIII. 2D 
