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The Science of Strips
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Text & Photographs by Tim Jackson
First published by Africa Geographic www.africageographic.com
Do you know why zebras are striped? Considering that it’s a conundrum that dates
back to when they were first described to science, you might think that we would
have figured it out by now. But, despite a plethora of explanations (Charles Darwin
and Alfred Russel Wallace clashed over the subject as long ago as 1891), no-one
knows the answer for sure. You be the judge – check out some of the ideas that people have put forward and remember that none of them has been shown definitively to be right or wrong,
no matter how fanciful they seem.
We do know at least that zebras are white with black stripes, and that the stripe patterns of
no two animals are alike. One idea suggests that these differences could work as a sort of bar
code that helps individuals, like this plains zebra (LEFT), to identify one another. In bright daylight, a zebra’s stripes are very striking (BELOW LEFT). But as the light fades, at dawn or dusk, they help to break up the animals’ outlines, giving them a ghostly appearance. A second idea is that they act as camouflage at times of the day when predators such as lions and hyaenas are likely
to be prowling. Alternatively stripes could help to hide an animal like a zebra in tall grass – an
explanation often criticised given that the species prefers open grasslands.
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These Grevy’s zebras (ABOVE RIGHT) might be using their stripes for climate control. At least that’s what one theory suggests – the black and white stripes could be creating a series of rotary breezes, or convection currents, through differential cooling. On another tangent, one hypothesis argues that the stripes may afford zebras protection against tsetse flies and the diseases they carry. Indeed these flies do prefer other species when it comes to feeding, and experiments using models of black, white and striped animals showed that the striped models attracted the fewest flies. Cryptic defence against tsetses, rather than lions, is a strong contender.
Stripes could make individuals, such as this Hartmann’s mountain zebra (LEFT), look bigger than they actually are. This optical illusion could cause a predator to misjudge the distance from its prey during a hunt, giving the zebra a better chance of escape.
Running zebras like these Hartmann’s mountain zebras (BELOW LEFT) could use their stripes to dazzle a predator – the confusion of stripes as a herd runs away may make it difficult to single out a specific individual.
Or, stripes could be used as a marker for grooming. Unlike this Cape zebra (BELOW RIGHT), which is grooming itself, the idea is that bold visual markings might direct others to groom specific areas of the body such as the mane and withers. Unlikely though it may sound, this theory argues that once grooming cues led to striping in these areas, their effectiveness could be increased if stripes were to spread over the entire body!
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And, finally, a group bonding theory points to the predisposition of zebras towards social interactions with other striped individuals. In other words, the more stripey you are, the more attention you’ll get – which makes for a well-groomed plains zebra foal (BELOW).
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Did you know?
The quagga, which went extinct 100 years ago, is a subspecies of the plains zebra from South Africa. In fact plains zebras from South Africa are more closely related to the quagga than to plains zebras from elsewhere in Africa. This means that the quagga is no longer treated as a separate species and the correct species name for the plains zebra is in fact Equus quagga and not Equus burchelli. The quagga’s markings were unusual in that it had stripes on its forequarters, while the hindquarters were almost solid brown. There are two other zebra species in Africa. Grevy’s zebra, which lives in arid areas of northern Kenya and Ethiopia, and the mountain zebra (for which two subspecies are recognised, the Cape mountain zebra from South Africa and Hartmann’s mountain zebra found in Namibia, Angola and South Africa).