Why aren't the biggest animals also the fastest?

July 19, 2017, 1:41 p.m.
Cheetah running
Photo: photobar/Shutterstock

They're strong, no doubt, but the largest land animals — giraffes, elephants, hippos — are not the fastest runners. And in the water, the biggest marine animals — like whales — aren't the fastest swimmers. Their bodies are just too massive to move that quickly.

But being small isn't necessarily an advantage, either, because the muscles are too little to propel the creature at a faster pace. So what's the animal-speed sweet spot? A group of scientists recently figured it out and published their scalable model in the journal Nature Ecology & Evolution.

"Scientists have always struggled with the fact that, in running animals, the largest are not the fastest. In nature, the fastest running or swimming animals such as cheetahs or marlins are of intermediate size," the authors write. "There have been numerous attempts to describe this phenomenon."

Researchers at the German Centre for Integrative Biodiversity Research in Leipzig, Germany, developed an algorithm that finds the best size to create the fastest animals, and it holds true whether the creature travels on land, in the water or in the air. Basically, it shows that an animal's top speed is all about acceleration.

"Animals are limited in their time for maximum acceleration because of restrictions on the quickly available energy. Consequently, acceleration time becomes the critical factor determining the maximum speed of animals," the researchers write.

Cheetahs (pictured above) are fleetest on foot with speeds topping 60 miles per hour. Falcons and hawks are the fastest in the air, and marlin are the quickest swimmers, all with speeds topping 80 mph.

While humans do fall within the sweet spot, we have invested more in outsmarting other species than in chasing or outrunning them, according to scientists.