A Stanford study has found that animals generally become larger as they evolve over time, providing convincing evidence for Cope’s rule, a theory named for American paleontologist Edward Cope, who stated that population lineages tend to experience larger body sizes due to evolution.

While Cope’s rule has long been confirmed in some animal groups, such as mammals and dinosaurs, the question of whether or not this was a universal trend remained contested.

To confirm the trend, a team of Stanford researchers, including associate professor of geological and environmental sciences Jonathan Payne, a paleobiologist at the Stanford School of Earth, Energy and Environmental Sciences, initiated one of the most comprehensive studies of evolution and body size ever conducted.

The research included 75 percent of all of the marine genera known in the fossil record as well as 60 percent of all animal genera known. The study was published in the Feb. 20 issue of “Science” and demonstrated that over the previous 542 million years the average size of marine animals has increased 150 fold.

Researchers believe that the extensive database created for this study will assist scientists in future research relating to evolutionary trends based on different traits or conditions.

Contact Zachary Samuel Brown at zbrown ‘at’ stanford.edu.