Evolution in Art: As Illustrated by the Life-histories of Designs

by Alfred C. Haddon

II. The Geographical Distribution of Animals and of Designs.

No part of the study of Biology is more fascinating than that which deals with the geographical distribution of organisms, especially when treated by such a master as Alfred Russel Wallace. The geographical distribution of art is as yet uninvestigated, but with careful and capable handling we may expect it to yield results not less interesting than those of the distribution of animals. It is needless to point out that the subject is peculiarly difficult, but as John Ray said two hundred years ago concerning the study of Natural History, “much might be done did we but endeavour, and nothing is insuperable to pains and patience.”

It will not be superfluous to here indicate the general lines upon which such an inquiry may be profitably made, taking the experience of zoologists as our guide in this matter.

It is a matter of general experience that animals are not uniformly scattered over the globe. The absence of all land mammals and of snakes from New Zealand; the occurrence of the monotremes only in Australia and New Guinea; that the American opossums are the only marsupials found out of Australia and a few adjacent islands; the absence of bears in Africa and of lemurs in America, are a few of the myriad cases in point.

By tabulating the denizens of different countries, the latter can be grouped according to their animals, and in this way zoologists have formed zoological regions, which may be further subdivided into sub-regions or provinces. All such divisions are characterised (1) by their characteristic animals, (2) by their peculiar animals, and (3) by the absence of certain groups of animals. The negative character in this case being perhaps the most valuable one.

Organisms may in a rough manner be distributed into zones corresponding with climate, which may be horizontal and largely dependent upon latitude, or vertical and directly dependent upon altitude, which varies, however, according to latitude. Such a kind of distribution is much more manifest in plants than in animals.

Further, there is a phenomenon known as “discontinuous distribution,” which is one of great importance. For example, the tapirs are only found in Central America and in the Malay Archipelago, the camel group in South America and the deserts of Asia, the ostrich group in South America, Africa, Australia, New Guinea, and New Zealand. It is needless to multiply examples. The explanation is simple enough. The tapirs are representatives of old generalised ungulates of early tertiary times that formerly lived in the northern hemisphere, but which have since become exterminated in the region of their origin and abundance, and have survived at only two extreme points of their old habitat. Ancestral camels are common in the tertiary beds of North America; the one group wandered southwards, and finding competition less keen on the plateaux of South America, were enabled to develop into llamas, alpacas, and so forth. The other group was modified so as to exist in the deserts of Asia, the less specialised forms in the intermediate countries having died out. The same general argument applies to the ostrich group, and in the rhea of South America, the ostrich of Africa, the cassowary of New Guinea, the emu of Australia, the diminutive apteryx and the gigantic extinct moas of New Zealand we have outliers, so to speak, of an extremely ancient group of birds, the other members of which have become exterminated in the intermediate districts.

Then again, there may be what are termed “local types and species,” forms which differ but slightly from the characteristic or “central” type of the species, and which are restricted to special regions. For example, in an island off a mainland there are often what are termed “insular varieties,” and in an archipelago it is of frequent occurrence that each island is characterised by possessing its peculiar varieties and even peculiar species. Isolated geographical features, such as commanding and separated mountains, may have what may equally be termed “insular faunas,” or again, the various valleys of a mountain chain may have appreciable faunistic differences.

The reason for this is not far to seek. These varieties differ from others merely by being intensified by local conditions and by isolation. Variation is more widespread than is generally supposed, but granting freedom of intercourse over a wide area and a stability of environment, the extreme variations are less liable to occur, and, furthermore, it is the average organism which is the most stable. Thus a fairly constant mean level is maintained. The isolation of portion of such a uniform population introduces new factors, and the isolated individuals tend to arrive at a condition of stable equilibrium which must of necessity be different from that of the parent stem.