Zebras are famous for their contrasting black and white stripes – but until very recently no one really knew why they sport their unusual striped pattern. It’s a question that’s been discussed as far back as 150 years ago by great Victorian biologists like Charles Darwin and Alfred Russel Wallace. Since then many ideas have…
Zebras are famous for their contrasting black and white stripes – but until very recently no one really knew why they sport their unusual striped pattern. It’s a question that’s been discussed as far back as 150 years ago by great Victorian biologists like Charles Darwin and Alfred Russel Wallace.
Since then many ideas have been put on the table but only in the last few years have there been serious attempts to test them. These ideas fall into four main categories: Zebras are striped to evade capture by predators, zebras are striped for social reasons, zebras are striped to keep cool, or they have stripes to avoid attack by biting flies.
Only the last one stands up to scrutiny. And our latest research helps fill in more of the details on why.
Could stripes help zebras avoid becoming a predator’s meal? There are many problems with this idea. Field experiments show that zebras stand out to the human eye when they’re among trees or in grassland even when illumination is poor – they appear far from camouflaged. And when fleeing from danger, zebras do not behave in ways to maximize any confusion possibly caused by striping, making hypothetical ideas about dazzling predators untenable.
Worse still for this idea, the eyesight of lions and spotted hyenas is much weaker than ours; these predators can only resolve stripes when zebras are very close up, at a distance when they can likely hear or smell the prey anyway. So stripes are unlikely to be of much use in anti-predator defense.
Most damaging, zebras are a preferred prey item for lions – in study after study across Africa, lions kill them more than might be expected from their numerical abundance. So stripes cannot be a very effective anti-predator defense against this important carnivore. So much for the evading-predators hypothesis.
What about the idea that stripes help zebras engage with members of their own species? Every zebra has a unique pattern of striping. Could it be useful in individual recognition? This possibility seems highly unlikely given that uniformly colored domestic horses can recognize other individuals by sight and sound. Striped members of the horse family do not groom each other – a form of social bonding – more than unstriped equid species either.
