concept

Heat-dissipation limit

The hypothesis that an animal's sustained metabolic output is capped not by how fast its gut can process food or how much its muscles can stand, but by how fast its body can get rid of waste heat. Put forward by John Speakman and Elżbieta Król, it inverts a long-standing argument in animal energetics: top speed is set by the legs, but how long a pace can be held is set by the radiators. An African elephant routes up to a fifth of its cardiac output through its ears for exactly this reason. In near-saturated air, where evaporation is nearly useless, the limit bites harder still.