A recent study fell short of explaining why zebras have their distinctive striped pattern. Is there really a good reason for zebras' stripes?
As we reported earlier, a recent study from scientists at the University of California, Davis examined the potential evolutionary reasons for the zebra’s distinctive striped pattern. The study suggested that a zebra’s stripes might not be as useful as once believed for camouflage purposes, but failed to offer a solid explanation for the pattern. Which leaves the question unanswered – why do zebras have stripes?
If the recent study found one thing, it’s that zebras probably don’t rely on their stripes to hide them from predators. By modeling the distances at which a number of predatory animals including lions, tigers, and spotted hyenas could see a zebra, researchers were able to infer that a predator would be able to hear and smell its prey before they could spot it in the night, rendering any camouflage effect useless.
“The results from this new study provide no support at all for the idea that the zebra’s stripes provide some type of anti-predator camouflaging effect,” said the lead author, Tim Caro, a professor of wildlife biology at UC Davis. “Instead, we reject this long-standing hypothesis that was debated by Charles Darwin and Alfred Russell Wallace.”
The study also ruled out social interaction as a potential reason for the zebra’s stripes. If stripes don’t help zebras hide from predators or recognize one another at a distance, then what is their purpose?
According to a BBC report, this isn’t the first time scientists have looked into the question. A study in 2012 from researchers at Lund University offers an interesting perspective. While the stripes on a zebra’s back are not believed to deter predators in a meaningful way, they could help keep pests at bay.
According to Susanne Akesson from Lund University, the team began by studying horses that had black, brown, or white coats. They found that light was horizontally polarized on the darker horses, making them a prime target for flies. Light bounced directly off of the white horses, however, resulting in unpolarized reflection. “Unpolarized light waves travel along any and every plane, and are much less attractive to flies. As a result, white-coated horses are much less troubled by horseflies than their dark-colored relatives.”
By setting up insect glue-covered boards with different patterns in a field, the researchers could determine which pattern attracted the most bugs. They found that a white-and-black striped pattern, similar to that of a zebra’s, attracted the least amount of flies by a large margin.
While the pest deterrent explanation may not be any better than the explanation by the recent UC Davis study, it brings to light just how complicated this seemingly simple question really is.
A press release from UC Davis describing the findings of the recent study can be accessed here.