Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 112, Issue 16, Pages 5093-5098Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1419823112
Keywords
macroevolution; adaptive evolution; evolutionary trends; Cope's rule; ancestral state reconstruction
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Funding
- Leverhulme Trust [RPG-2013-185]
- University of Reading PhD studentship
- Biotechnology and Biological Sciences Research Council (BBSRC) [BB/K004344/1]
- European Research Council
- BBSRC [BB/L018594/1, BB/K004344/1] Funding Source: UKRI
- Biotechnology and Biological Sciences Research Council [BB/L018594/1, BB/K004344/1] Funding Source: researchfish
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The notion that large body size confers some intrinsic advantage to biological species has been debated for centuries. Using a phylogenetic statistical approach that allows the rate of body size evolution to vary across a phylogeny, we find a long-term directional bias toward increasing size in the mammals. This pattern holds separately in 10 of 11 orders for which sufficient data are available and arises from a tendency for accelerated rates of evolution to produce increases, but not decreases, in size. On a branch-bybranch basis, increases in body size have been more than twice as likely as decreases, yielding what amounts to millions and millions of years of rapid and repeated increases in size away from the small ancestral mammal. These results are the first evidence, to our knowledge, from extant species that are compatible with Cope's rule: the pattern of body size increase through time observed in the mammalian fossil record. We show that this pattern is unlikely to be explained by several nonadaptive mechanisms for increasing size and most likely represents repeated responses to new selective circumstances. By demonstrating that it is possible to uncover ancient evolutionary trends from a combination of a phylogeny and appropriate statistical models, we illustrate how data from extant species can complement paleontological accounts of evolutionary history, opening up new avenues of investigation for both.
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