New Evolutionary Theory Explains Why Some Animals Shrink Over Time

Research Challenges 'Cope's Rule', Identifies Key Ecological Factors Influencing Animal Size

New theoretical research suggests that animal size over time depends on two key ecological factors: the intensity of direct competition for resources between species, and the risk of extinction from the environment.
The research challenges the traditional 'Cope's Rule', which suggests that animal groups tend to evolve larger body sizes over thousands and millions of years.
Using computer models simulating evolution, the study identified three distinct patterns of body-size change emerging under different conditions: gradual size increase over time, size increase followed by extinctions, and gradual size decrease over time.
The findings help explain why some species, such as Alaskan horses, cryptodiran turtles, and island lizards, have shrunk over time.
The research team, led by Dr. Shovonlal Roy, an ecosystem modeler from the University of Reading, hopes to see future research take on the recurrent inverse Cope’s Rule and assess its validity in the fossil record.