New research reveals key factors behind the changing sizes of certain animals over time, challenging traditional evolutionary theories with its findings on species ’ size variations.

The mystery behind why Alaskan horses, cryptodiran turtles, and island lizards shrunk over time may have been solved in a new study.

The new theoretical research proposes 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.