There Were 18 Theories About Why Zebras Have Stripes

Saturday August 11, 2018 Written by Taz

Racing Stripes
Image: Greg Willis, Creative Commons licence CC BY-SA 2.0

It’s a riddle that nettled no less a mind than Charles Darwin: what evolutionary advantage does a black and white striped coat wield on the African savannah? Camouflage? Powers of seduction? Thermoregulation? Protection against bugs?

In their endeavours to ascertain the truth of the matter, scientists have been split pretty evenly across these four camps (each with their own subdivisions, taking the total number of theories to 18). A few years back, researchers at the University of California thought they’d proven the bug-protection hypothesis when they found that horseflies preferred landing on non-striped hides over striped ones. That theory could hold even more weight now that scientists at Hungary’s Eötvös Loránd University think they’ve disproven the thermoregulation model.

To test the theory, the researchers filled six metal barrels with water and covering them with the pelts of a black cow, a white cow, a grey cow, a grey horse, a fake zebra and a real zebra, then left them out in the open air for four months and monitored their core temperatures. As their research paper boldly asserts, “We found that there were no significant core temperature differences between the striped and grey barrels, even on many hot days, independent of the air temperature and wind speed”. By way of conclusion? You may now consider the hypothesis that zebra stripes play a thermoregulatory role debunked.

To clarify the magnitude of what’s been repudiated here, proponents of the thermoregulation theory held that zebra stripes cooled the animal’s body by producing convective air eddies that arose from the alternating temperature gradients of the differently shaded stripes. “This hypothesis seems reasonable”, granted the paper, “because in sunshine the black zebra stripes are warmer due to their stronger absorption of sunlight compared to the cooler white stripes of higher reflectance.” So everyone’s basically still friends.