Cope's rule proposes that animal lineages evolve toward larger body size over time. To test this hypothesis across all marine animals, we compiled a data set of body sizes for 17,208 genera of marine animals spanning the past 542 million years. Mean biovolume across genera has increased by a factor of 150 since the Cambrian, whereas minimum biovolume has decreased by less than a factor of 10, and maximum biovolume has increased by more than a factor of 100,000. Neutral drift from a small initial value cannot explain this pattern. Instead, most of the size increase reflects differential diversification across classes, indicating that the pattern does not reflect a simple scaling-up of widespread and persistent selection for larger size within populations.
CITATION STYLE
Heim, N. A., Knope, M. L., Schaal, E. K., Wang, S. C., & Payne, J. L. (2015). Cope’s rule in the evolution of marine animals. Science, 347(6224), 867–870. https://doi.org/10.1126/science.1260065
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