The San of the Kalahari know how the zebra got its stripes. Long ago, a stripeless zebra got into an argument with a baboon, who was tending a fire. The zebra got so cross that he kicked the baboon, who landed on his behind — giving him a raw red bottom. But then the zebra stumbled, fell in the fire, and the burning sticks left stripe marks.
These days, evolutionary biologists are pretty sure that the San got it wrong. But they aren’t doing much better at providing an alternative explanation. Despite numerous theories, they can’t agree on the actual answer: how did the zebra get its stripes?
“We go to the moon. We do all sorts of incredible things,” Hamish Ireland, from the University of Edinburgh, said. “But we still don’t know why zebras are striped. It’s so intriguing.”
A study in 2019 dressed horses in zebra stripes to find if it conferred an advantage to deter biting flies
ALAMY
This isn’t for want of trying. Whenever people see a zebra, it seems they want to know why it is stripey. In only the past decade, some scientists have confidently argued that it is to do with thermoregulation. Black stripes get hotter, and so when layered with white it promotes airflow.
This, argues Ireland in the journal Biological Reviews, falls down in a few areas. The spacing and distribution of stripes is wrong. The swishing of the tail counteracts it. Having a black stripe that gets warm so you can get cool is also a pretty idiosyncratic approach to thermoregulation.
Maybe the answer is flies? Others have dressed horses in zebra coats, and shown that biting insects seem to get confused — and not just because it’s a horse in fancy dress. Stripes, they maintain, are for deterring insects.
This may be an advantage, Ireland concedes, in his review of the state of stripiness science. But is it enough of an advantage to justify walking about in the savannah in front of lions with “massive great big stripes on you”? “Most of the animals choose to be inconspicuous. If there are lions about, you don’t get worried about being bitten by a fly.”
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Ah, but what about the others who argue this is missing the point: massive great big stripes are actually an advantage here too. The sharp angular lines are “dazzle camouflage”, confusing lions who apparently get so bemused that the zebra just hops away. Evidence for this, though, is scant.
This theory also falls down on an argument that also undermines all the others. If stripes are so good, for whatever reason, why aren’t they everywhere? “Why are all the other animals that live in the same environment next to them not striped?” Ireland said. What we need is a theory that explains why stripiness is good for zebras, but not equally so for other animals.
One idea that Ireland is interested in, is that of signalling. Zebra are different from other animals in that they do not chew the cud — so have less dietary overlap with them. This means they can form mixed herds with, for instance, wildebeest. Close up, stripes are conspicuous, allowing zebras and these other grazers to spot them and get together in safer herds. From a distance they blur, still allowing some camouflage.
Maybe that is indeed part of the story. But the truth is, says Ireland, we just don’t have a compelling answer and that is itself fascinating. “There’s many things in nature that we don’t know. But this isn’t some deep biochemical thing where you need a big lab. You don’t need atomic physics or advanced mathematics. It’s just there in front of you. You can see it.”