Vertebrates, Invertebrates and Plants

A second study which argued in support of Cope’s rule was that done by Kingsolver and Pfennig (2004) and covered a much wider range of organisms including vertebrates, invertebrates and plants. The main purpose of the paper was to determine whether individual-level selection could be viewed as a mechanism for Cope’s rule (Kingsolver and Pfennig, 2004). This study was very extensive and gathered data from many previously performed studies. The authors had three main criteria for data inclusion. These were:

Cretaceous leaf from Woodbine Sandstone, Texas
that there was natural variation in the quantitative traits in the study population, that fitness had been measured in natural field conditions, and that selection was measured in a standardized fashion so that studies could be compared equally (Kingsolver and Pfennig, 2004).