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The question of why zebras have stripes is not, so to speak, black and white.

In the online journal Royal Society Open Science, University of California, Davis, professor Tim Caro and Cal State Long Beach assistant professor Theodore Stankowich find both agreement and disagreement with another zebra study.

“Our short paper brings together different ideas about the reasons that zebras have black and white stripes,” Caro said. 

The biologists compared their own previous findings to those of a team led by Brenda Larison of UCLA that appeared in a January 2015 Royal Society Open Science article, “How the zebra got its stripes: a problem with too many solutions.”

Larison’s team studied one zebra species — the plains zebra — and concluded that the amount and intensity of striping was associated with warmer temperatures and high precipitation.

In an earlier April 1, 2014, study called “The function of zebra stripes” in the journal Nature Communication, Caro, Stankowich and co-authors studied all seven species of equids (zebras and horses), and found that avoiding biting flies, including horseflies and tsetse flies, is the evolutionary driver for zebra stripes.

“Here we want to stress that these two studies agree on a number of points that move detective work on the mystery of zebra stripes forward considerably,” the authors write in the new commentary.

 The studies both:

• Agree that aspects of striping are associated with warm, humid conditions, and both indirectly point to avoiding biting flies as a driver of striping.
• Dismiss hypotheses that say stripes evolved to confuse predators, such as lions, or to serve as camouflage in wooded habitats.
• Question or dismiss the idea that stripes can generate cooling eddies on the zebra’s body.
• Are hampered by not knowing the extent to which temperature and humidity predict fly annoyance.

They differ in their interpretation of why striping is associated with warm, humid conditions. Larison’s group suggests that zebra stripes serve as a means to cool off the animal because they had found more intense striping in environments with higher temperatures. They focused on temperature as the most powerful of their findings, while Caro’s team found environments favored by biting flies to be the greater driver.

“We think there’s a clear mechanism for how stripes can deter biting flies and thereby prevent the spread of diseases,” Stankowich said. “But we have yet to see a clear mechanism for how striping can influence body temperature.”

One thing on which both studies can agree: More research is needed to understand fully why zebras have black and white stripes.