Susanne Åkesson, a biologist at Lund University in Sweden, refutes the theory that zebras have striped fur to stay cool in the hot sun. That hypothesis is wrong, she and her colleagues show in a study recently published in Scientific Reports.
There has been an ongoing discussion among researchers, dating back to Darwin, on why zebras have their signature black and white stripes.
One of several theories is that it keeps them cool in the sunshine. The black stripes get warmer than the white areas, and the theory states that this creates small vortexes when the hotter air above the dark fur meets the cooler air above the white fur. According to the theory these vortexes works as a fan to cool the body.
To test this theory, the researchers filled big metal barrels with water and covered them with skin imitations in different colours: black and white stripes, black, white, brown and grey. They then placed the barrels in the sun and later measured the temperature in each barrel. Not surprisingly, the black one was the hottest and the white one the coolest. The striped and grey barrels were similar, and in these the temperature did not go down.
“The stripes didn’t lower the temperature. It turns out stripes don’t actually cool zebras,” says Susanne Åkesson. Paper. (open access) – Gábor Horváth, Ádám Pereszlényi, Dénes Száz, András Barta, Imre M. Jánosi, Balázs Gerics, Susanne Åkesson. Experimental evidence that stripes do not cool zebras. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-27637-1 More.
This experiment probably won’t settle the matter but it does point up a curious fact about Darwinian thinking: the assumption that a striking trait evolved as a result of conferring a survival benefit. If that is not the case, Darwinian thinking is getting in the way. It’s the same problem as when a Darwinian explanation is sought for the low immune resistance in in some migratory birds: Maybe it isn’t a benefit to the birds but they are stuck with it. Haven’t tens of thousands of species that we know about gone extinct? Extinctions don’t usually happen right away; it may take a very long time before the fact that something isn’t really a benefit becomes a problem. Meanwhile, we may be confusing the matter by telling just-so stories about the benefit.
And, as for zebras, see also: Study: Zebra stripes neither hide nor flaunt
Stripes offer no advantage to zebra?
How the zebra got its stripes, this time really
How the zebra got its stripes, maybe
How the zebra did NOT get its stripes?