CLIMATE AND CLIMATIC SPECIES AND VARIETIES. Although a half century ago it was generally held that changes of climate have not profoundly affected organisms, yet the recent detail study of variation has shown that climate MYsitocal influences have been th*-canses of origin of probably a very large number of the species contained in our museums and described in biological literature. Among insects, birds and mammals it has been estimated that from a third to a half of the known species are climatic or local species or varieties, or local races. As is well known, Americans born of foreign parentage are larger than their ancestors, whether English, Irish, Germans or French; and Boroditch has shown that the children of Americans of both sexes born in the United States are larger than those of foreign races. Certain modifica tions in the cephalic index have also been ob served. This is generally attributable to dif ference in the climate of the Old and New Worlds, our American climate being drier, more changeable and stimulating than that of Europe. It appears that the introduced English sparrow has undergone a gradual modification since its introduction into this country about 40 years ago. Bumpus has critically examined over 1,700 eggs of this bird, one-half from England and the other half from Providence, R. I. It was found that the eggs of the Amer ican race or breed vary more than the European, that they are smaller and of a strikingly different shape, being more round.ed and with a much greater amount of color varia tion. This is attributed by the author to a suspension of natural selection. However this may be, it belongs with the class of facts which show that the modification is primarily due to the change from one climate to another. Cock erel] has found that a common European snail (Helix nemoralis), introduced into this coun try soon begins to present variations not known to exist in England, while of the introduced butterfly (Pieris napi), 12 American varieties, and of P. rapa, four varieties have appeared on American soil within the few years which have elapsed since their appearance and spread on this continent. Where different mammals
are transported from temperate to tropical countries the wool tends to become replaced by hair, and other changes occur. The turkey does not vary in temperate regions, but .when accli mated in India it degenerates in size, is inca pable of rising on the wing, becomes black and the long pendulous appendages over the beak develop enormously. Cold has naturally the inverse effect; mammals transported to the north from the tropics become more or less woolly. As the result of the severe winters and the elevation of Angora in Asia Minor, the cats, shepherd dogs, goats and hares are clothed with a long fleece-like wool.
Islands present different climatic features from the mainland, being damper, etc., and hence the birds, reptiles and other animals present slight but constant differences from their allies and probable ancestors on the near est continents. Not only that each group, as in the case of the Galapagos Islands, but even each island is tenanted by a distinct local variety of birds. This has also been noticed by Wallace in the East Indian Archipelago. The swallow-tail butterflies of islands tend to have shorter tails, and the outlines of the wings differ. Thus the local races become incipient species, and by being isolated are prevented from crossing with the original stock or species, and in this way geographical varieties or repre sentative species are produced. When great changes have taken place in the topography, portions of land cut off from the continent, or continents become divided, species have arisen. Thus in the late Tertiary, Asia and Ainerica were continuous, but when Bering Strait was formed, the bison of this country and that of Europe (aurochs) became specialized, becom ing different species. In this way multitudes of species have probably arisen over all parts of the world. See DISTRIBUTION OF LIVING MAM MALS ; PLANT GEOGRAPHY.