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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1977 Nov;74(11):5083–5087. doi: 10.1073/pnas.74.11.5083

Is evolution gradual or rectangular? Evidence from living fishes.

J C Avise
PMCID: PMC432103  PMID: 270743

Abstract

The traditional view that most evolutionary change is gradual and cumulative within lineages (phyletic gradualism) has recently been challenged by the proposition that the majority of evolutionary change is concentrated within speciation events (rectangular evolution). The logical implications of these competing hypotheses for the means and variances of genetic distance among living members of rapidly and slowly speciating phylads are examined. An example of a critical test of gradual versus rectangular evolution is provided by electrophoretic analyses of genic composition in 69 species of North American Cyprinidae (minnows), and 19 species of Centrarchidae (sunfish). Rate of protein evolution appears somewhat decelerated, if anything, in the rapidly speciating minnows. Results are inconsistent with predictions of rectangular evolution, but are not demonstrably incongruent with predictions of phyletic gradualism.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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