The science of life : fully illustrated in tone and line and including many diagrams

BOOK 3

southern individuals. This particular case does not present a very puzzling problem to the systematist. ‘There is no question of dividing the European wolf into two or more species, for the extreme types are connected together by a grading series of intermediate forms, all breeding freely together. They are simply variations within the limits of a single species.

But when we take into consideration all the wolves in the world, the problem of variation becomes more serious. ‘The true wolf ranges over the whole of the northern hemisphere from the Arctic Circle to south temperate latitudes, and apart from such “ sports” as complete blackness, which may turn up anywhere, the characters of wolves vary in accordance with the climate of the particular region they inhabit. Northern wolves, for example, are on the average larger than the southern and have a thicker and whiter coat, and in temperate zones the wolves inhabiting comparatively dry country are on the whole paler in tint than those from districts where the rainfall is heavy. And there are variations in build and proportion. Now, sometimes these differences are considerable enough to make it doubtful whether the forms should be grouped in the same species or not. There are, for example, the American timberwolf, the pale wolves of North-Western India, the small, short-legged Japanese wolf, the little red wolf of ‘Texas—these and many others, all fairly distinct from the common wolf of Europe, but just similar enough to leave us in doubt whether they should be separated or left together. Confronted with this problem, the experts differ among themselves. Some prefer to distinguish these various kinds as separate species; some include them all within the species Canis lupus and distinguish them as local races or sub-species. Moreover, this variation is not a canine peculiarity ; the foxes show it, ‘too, and, indeed, nearly every wide-ranging kind of animal or plant has its local varieties and therefore its problems for the systematist.

This sort of difficulty is not confined to the first step in classification. It attends also the formation of groups of higher grades. It is often very hard to tell whether species are sufficiently like each other to be put in the same genus, or whether genera are sufficiently like each other to be put in the same family.

Tt will make the point clearer if we take another example, not this time from the dogs but from their cousins the cats. As is well known, the lion, tiger, leopard, lynx, and the rest are all plainly related to the smaller cats, and until recently they have

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always been called different species of one genus; the lion, for example, was Felis leo, the tiger Felis tigris, the leopard Felis pardus, the tame cat Felis catus, and so on. But, as a matter of fact, the group is divisible into two subdivisions, on the one hand the lion, tiger, leopard, and jaguar, and on the other the puma, lynx, and all of the smaller cats ; their most striking distinction is that while only the former group can roar, only the latter can purr (limitations which have an anatomical basis). Here arises the first difference of opinion: Some authorities call the two groups sub-genera, while others call them genera with the names Panthera and Felis respectively. Now each of the commonly accepted species shows considerable variation, and here the second difference arises. The tiger, for instance, is big and long-haired at the northern end of its range, smaller and short-haired in India, very small indeed in Sumatra, unusually closely striped in Turkestan. Some authorities regard the various forms as local varieties or subspecies of the species tiger and denote them by adding a third name, the sub-species name, to the already elaborate titles—thus the Manchurian tiger is Panthera tigris longipilis, the Sumatran tiger is Panthera tigris sondaica, and so on. Others, however, consider that they are distinct enough to be called so many species, in which case the old tiger species is made a genus, the different kinds becoming Tigris longipilis, Tigris Sondaica, and so on.

These differences of opinion, be it noted, are not signs of incompetence on the part of the systematists; they result from the nature of the facts, which do not admit of categorical classification. It is written that Noah collected ‘‘ every beast after its kind, and all the cattle after their kind, and every creeping thing that creepeth upon the earth after its kind, and every fowl after its kind, every bird of every sort,’ and even nowadays most people share the delusion implicit in this passage—that if we could assemble together every individual beast and creeping thing and fowl that live in the world to-day, and if we could examine and compare them all, it would be possible to group them with neatness and precision into definite kinds, or species. But thatisa myth. What has been said of dogs and cats is true of other animals —and of plants and microscopic creatures as well. There exists every conceivable grade of difference between organisms. There are animals which are very much alike, so much alike that they are obviously members of the same species. ‘There are animals which are