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      Early bursts of body size and shape evolution are rare in comparative data.

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          Abstract

          George Gaylord Simpson famously postulated that much of life's diversity originated as adaptive radiations-more or less simultaneous divergences of numerous lines from a single ancestral adaptive type. However, identifying adaptive radiations has proven difficult due to a lack of broad-scale comparative datasets. Here, we use phylogenetic comparative data on body size and shape in a diversity of animal clades to test a key model of adaptive radiation, in which initially rapid morphological evolution is followed by relative stasis. We compared the fit of this model to both single selective peak and random walk models. We found little support for the early-burst model of adaptive radiation, whereas both other models, particularly that of selective peaks, were commonly supported. In addition, we found that the net rate of morphological evolution varied inversely with clade age. The youngest clades appear to evolve most rapidly because long-term change typically does not attain the amount of divergence predicted from rates measured over short time scales. Across our entire analysis, the dominant pattern was one of constraints shaping evolution continually through time rather than rapid evolution followed by stasis. We suggest that the classical model of adaptive radiation, where morphological evolution is initially rapid and slows through time, may be rare in comparative data.

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          Author and article information

          Journal
          Evolution
          Evolution; international journal of organic evolution
          Wiley
          1558-5646
          0014-3820
          Aug 2010
          : 64
          : 8
          Affiliations
          [1 ] Department of Biological Sciences, University of Idaho, Moscow, Idaho 83844, USA. lukeh@uidaho.edu
          Article
          EVO1025
          10.1111/j.1558-5646.2010.01025.x
          20455932
          7d58a2cd-eafa-4fd9-b718-e730c49ff6b2
          History

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