PACHYDERM NAPS: Elephants and other large herbivores may sleep little because their low-quality diets demand constant foraging.© ISTOCK.COM/JFOLTYN
Humans typically sleep between six and eight hours per night. Some bats doze for a whopping 15 or 20 hours. Large animals, such as giraffes and elephants, snooze less than four hours a day. What explains such diversity in sleep times across mammals? Although a concrete answer is still lacking, ideas abound about how and why sleep patterns evolved.
One popular hypothesis is that, because larger animals have to eat so much to maintain their big bodies, they don’t have time to sleep a lot. “An elephant has to spend between 17 and 19 hours per day eating,” says Suzana Herculano-Houzel of Brazil’s Institute of Biomedical Sciences at the Federal University of Rio de Janeiro. “Because there’s only 24 hours in a day, elephants and ...
