File:Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals (1907) (14750184726).jpg

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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en region is made up of the various species ofanimals living naturally within its borders. The flora of aregion is made up of the plants which grow naturally withinits limits. Of all these, animals and plants, the inhabitantsof most regions are apparently largely migrants from someother region. Some have entered the region in questionbefore acquiring their present specific characters; others comeafter having done so. Which of these conditions apply to anygiven case can sometimes be ascertained by the comparisonof the individuals along the supposed route of migration. Thus, Dr. C. Hart Merriam has undertaken to show theactual origin of nine species of Californian chipmunks (Eutamias)by an elaborate study of their distribution, adaptations, andtransformations. He finds them closely related to one another, 1 A paper published in Science, 1906, by the senior author, underthe title The Actual Origin of Species, has been freely quoted from inthis chapter. 9 117 118 EVOLUTION AND ANIMAL LIFE
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FIG. 71.—Some chipmunks of California, showing distinct species produced throughisolation. (From nature, by William Sackston Atkinson.) GEOGRAPHIC ISOLATION AND SPECIES-FORMING 119 but not derived from one another by direct lines of descent. Acloser study indicates that some of them came from closelyrelated forms in remote geographic areas, others from antece-dent forms now extinct, and not more than three or four fromspecies still inhabiting the region. The nature of any fauna bears an immediate relation tothe barriers, geographic, climatic, topographic, or bionomic,which may form its boundaries. By bionomic barriers wemean any condition of any sort which may check free inter-breeding, or which may tend to cause divergence within aspecies. A thickly peopled level area may be in this sense abarrier, because it prevents the animals on the one side of thearea from interbreeding with those on the opposite side. Ifthe two extremes have diverged to become different species,the individual

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