Identifier: evolutionanimall00jord (find matches)
Title: Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals
Year: 1907 (1900s)
Authors: Jordan, David Starr, 1851-1931 Kellogg, Vernon L. (Vernon Lyman), 1867-1937
Subjects: Evolution
Publisher: New York, D. Appleton and Company
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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turtle. The waterfall which limits the ascent of the fishis the chosen home of the ouzel. The mountain barrier whichthe bobolink or the prairie dog does not cross may be the centerof distribution of the little chief hare or the Arctic bluebird. The term fauna is applied to the animals of any regionconsidered collectively. Thus the fauna of Illinois comprisesthe entire list of animals found naturally in that State. Itincludes the aboriginal man, the black bear, the fox, and all itsanimal life down to the Amceba and the microbe of malaria.The relation of the fauna of one region to that of another de-pends on the ease with which barriers may be crossed. Thusthe fauna of Illinois differs little from that of Indiana or Iowa,because the State contains no barriers that animals may not GEOGRAPHICAL DISTRIBUTION 317 readily pass. On the other hand, the fauna of California orColorado differs materially from that of the adjoining regions,because the mountainous country is full of barriers which
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obstruct the diffusion of life. Distinctness is in direct propor-tion to isolation. What is true in this regard of the fauna ofany region is likewise true of its individual species. The degree 318 EVOLUTION AND ANIMAL LIFE of resemolance among individuals is in strict proportion to thefreedom of their movements. Variation within the limits ofa species is again proportionate to the barriers which preventequal and free diffusion. The various divisions or realms into which the land surfaceof the earth may be divided, on the basis of the character of theanimal life, have their boundary in the obstacles offered to thespread of the average animal. In spite of great inequalitiesin this regard, we may yet roughly divide the land of the globeinto seven principal realms or areas of distribution, each limitedby barriers, of which the chief are the presence of the sea andthe occurrence of frost. There are the Arctic, North Tem-perate, South American, Indo-African, Patagonian, Lemurian,and Austral

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