Why do zebras have stripes? Biologists say they finally have the answer

Five explanations have been suggested in the past, but scientists say a new study looking at the geographical distribution of stripes holds the answer

Scientists say that they have finally solved one of the most intriguing mysteries of the animal kingdom: how the zebra got its stripes.

Ever since Charles Darwin debated the topic with fellow 19th century biologist Alfred Russel Wallace, biologists have been suggesting possible evolutionary drivers that led to the development of these bold black and white markings.

Now, a team from the University of California say that they have analysed the competing theories and concluded that the zebra’s stripes evolved over time to protect the animals from the unwanted attentions of disease-carrying flies.

“No one knew why zebras have such striking coloration,” said lead author Tim Caro, a professor of wildlife biology. “But solving evolutionary conundrums increases our knowledge of the natural world and may spark greater commitment to conserving it.”

Caro and his team looked at five different hypotheses, including the possibility that the stripes were a form of camouflage, that they confused predators or helped moderate body temperature, or even that they were key to zebras’ social interaction.

The team concluded that the stripes were a defence against eco-parasites after looking at variations in striping patterns across the seven living species of the equid group (the family of animals that includes horses, donkeys and zebras) and their 20 subspecies – most of which have striping on their body to various degrees.

They then mapped the intensity if these stripes against the various environmental factors that might have influenced the evolution of these markings, including the distribution of forests, predators and biting flies.

The results, published 1 April in the journal Nature Communications, show that the strongest statistical correlation is between species of distinct stripes and areas where parasites are most active.

“I was amazed by our results,” Caro said. "Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.”

“I was delighted to see the results were so strong in one direction.”

However, even this explanation does not quite close the case on zebra stripes. Although biologists are now fairly sure that the markings are there to keep biting flies away, the question remains: why do these insects avoid striped surfaces in the first place?