The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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Directional selection is a type of natural selection that emphasizes one type of mutation that eventually phenotypically manifests itself within the population. The darkened wing color of the peppered moth (Biston betularia) located in industrial areas is an example of directional selection. The darker wings provided appropriate camouflage from predators as the moths dwelled on soot-covered trees.
Directional selection is commonly instigated by the human population on other species for a particular use. A plant breeder may only choose to grow seed from a plant with a particular characteristic or set of characteristics. Eventually, successive breeding of the plant will alter the population and the desired characteristic will become the common phenotype. Dog breeding is an example of directional selection applied by humans.