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Science 22 July 1983:
Vol. 221. no. 4608, pp. 387 - 389
DOI: 10.1126/science.221.4608.387
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Articles

Macroevolutionary Trends: New Perspectives on the Roles of Adaptation and Incidental Effect

ELISABETH S. VRBA 1

1 Transvaal Museum, Pretoria 0001, South Africa

Trends, long-term directional tendencies in evolution, are traditionally interpreted as selected for and adaptive. Alternatively, trends may be unselected effects of characters and processes within species: the effect hypothesis. Thus adaptations of organisms, varying among species, were selected for immediate fitness, but they may also incidentally determine different speciation and extinction rates and trends.

Submitted on July 30, 1982
Accepted on March 16, 1983


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