Before we proceed to describe the va rieties of the human race, it is necessary to consider, what constitutes a species in zoology; and how varieties arise out of species.
We should answer, in the abstract, to the first question; that all animals belong to the same species, which differ in such points only, as might arise in the natural course of degeneration, while those dif ferences, which could not be explain ed on this supposition would lead us to class the animals which exhibit them in different species. But the great dif ficulty arises, in distinguishing in actual practice mere varieties from specific dif ferences.
Ray, and after him Buffon, referred those animals to the same species which copulate together, and produce a fertile offspring. But this criterion has pro duced very little benefit ; and we proba bly must be contented to derive our no tions of species in zoology from analogy and probability. The molar teeth of tie Asiatic and African elephants differ very widely in their conformation ; and, as we know no instance of such a dif ference produced by mere degeneration, we ascribe those animals to species ori ginally different. The white ferret on the contrary we regard as a variety, be cause we know that the colour of the hair and pupil experiences a similar va riation in other instances where it is a mere variety.
In considering the causes by the ope ration of which species degenerate into varieties, we shall be contented with stating the facts which prove the influ ence of such causes ; without attempting to explain how they produce their ef fects. As there is very little of a satis factory nature ascertained respecting this matter, we should be afraid of dis gusting the sensible reader by substitut ing speculation in the place of more solid information.
A very slight consideration will shew that there is no point of difference be tween the several races of mankind, which has not been found to arise, in at least an equal degree, among other ani mals, as a mere variety, from the usual causes of degeneration. The instances of this kind are derived chiefly from do mesticated animals, as they are exposed to all those causes which can produce such effects ; by living with man they lead an artificial and unnatural kind of life, and are taken with him into climates and situations, and exposed to various other circumstances altogether different from their original destination ; hence they run into numerous varieties of co lour, form, size, &c. which, when they
are established as permanent breeds, would be considered by a person unin formed on these subjects, to be origi nally different species. Wild animals on the contrary remaining constantly in the state for which they were originally framed, retain permanently their first character. Man, the inhabitant of every climate and soil, partaking of every kind of food, and of every variety in mode of life, must be exposed still more than any animal to the causes of degene ration.
Climate is one of the causes which seems to exercise a powerful influence on the animal economy, and the forma tion of the body. To this we must ascribe the white colour of several animals in the northern regions, which possess other colours in more temperate countries, viz. the fox, hare, falcon, crow, blackbird, &c. That this whiteness must be ascrib ed to the cold of the climate is rendered probable by the analogy of those animals which change their colour in the same country at the winter season to white or grey : as the ermine and weasel, hare, squirrel, reindeer, &c. &c. The com mon bear is very differently coloured in different countries. The remarkable silky and white covering of various ani mals in that district of Asia Minor called Angora must be explained in the same way, rather than from any difference of food ; because it . occurs in instances where very different kinds of food are used, as in the cat and goat. Hence also we account for the peculiar blackness of the fowls and dogs on the coast of Gui nea, and for the change of the woolly co vering of the sheep into hair in the same situation.