Why Males and Females Differ in Size: Unpacking the Evolution of Body Size in Tetrapods

Why are male lions larger than females, while in some frog species, females significantly outweigh their male counterparts? This phenomenon—known as sexual size dimorphism (SSD)—is common across the animal kingdom. A new global study published in Nature Ecology & Evolution sheds light on the evolutionary origins of SSD by analyzing body size changes in over 11,000 tetrapod species, including mammals, birds, amphibians, and reptiles.