*edit: This post was initially written for a website which a few months ago became defunct and was shut down; the post was then published on Medium. I Am publishing here on my site was a few edits to bring it up to date in 2019.
There are two animals that are probably the most recognizable to individuals regardless of where they’re from, the first is the Giraffe (that long neck!), the second is the Zebra and their stripes. If you consider that Zebra is the only animals that has stripes (well, there are others but we’ll get to that shortly) it’s no big surprise that one of the first questions I get asked on one of our Durban safari tours is; why do Zebra have stripes?
Proposed Reasons Why Zebra Have Stripes
There are a number of theories about why the Zebra has stripes, the most popular reasons are (in no particular order);
- Camouflage — helps to avoid be a meal.
- Identification — striped are unique so may help Zebra identify one another.
- Temperature regulation — the striped assist with keeping the animal cool.
- Ectoparasite — the strips confuse biting fly parasites like tsetse fly.
The fact is that even today, we do not know why a Zebra has stripes — though I have a very strong opinion that has to do with temperature regulation (well it’s on the list but my idea differs to the established idea). I’m going to take each argument in it’s turn and explain why I don’t think they are correct — if you want to skip all that (hopefully you’ll fascinated with my arguments and wont skip) and just read up on why I think my idea’s the right, then simply scroll to the end.
A Brief History of Zebra
Before we get to the arguments, I thought I’d just go over the history of Zebra. Turns out that Zebra belong to a class of species called Equus which includes Horses and Donkeys; they all share a common dog-sized ancestor living in North America some 50 million years ago. Over time the species crossed over a land bridge into Europe and continued to happily evolve into a wide range of different species.
About 5,5 million years (give or take) the majority of sub-species disappeared leaving just the sub-species that we are familiar with grazing peacefully — the Horse, Donkey and Zebra. Finally, some 4,5 million years ago, one of those sub-species meandered south into the African continent where they took on a peculiar appearance, the stripes that are so distinct in the African veld.
So why would that be? What caused the Zebra to alter it’s appearance so dramatically? A single event like reacting to a new homeland or was it a combination of events? We simply don’t know, but here are the suggested possibilities and my arguments against.
Camouflage is usually everyone’s first go-to when trying to understand why the Zebra has stripes. It’s not the correct answer to our question, but I can understand why people think it is. The alternating stripes do assist in breaking up the Zebra’s silhouette which means a predator scanning the veld for a meal could simply overlook the Zebra.
The thing is though, and this is a question that is going to be asked over and over again; if the stripes are effective as a camouflage pattern, why do we not see this pattern repeated in other animal species? The closest that I can think of that has a striping is the Blue Wilderbeest and it’s very subtle.
Contrary to popular belief that predators see only in black and white, predators do see in color, but their color range is very limited compared to humans, for predators it’s all about movement, which means camouflage is not going to help that much.
Anyone has has every watched Zebra for any amount of time will notice a peculiarity of Zebra — their tails never stop swishing from side to side — seems a bit pointless then to have effective camouflage yet give the game away by constant movement. Zebra are also constantly moving about in general, they don’t have the stillness like Nyala do.
The other thing to consider is that predators generally speaking have excellent night vision — does having black and white stripes offer any advantage in terms of camouflage at night? It seems unlikely that this would be effective though a study may prove me wrong. I should also point out they predators don’t rely on eye sight alone, they all generally have fantastic hearing and sense of smell.
Some authors have put forward an argument that a herd of Zebra standing together can appear as one large animal thanks to the striping effect. When Zebra do run from predators they flee as a group, mares in calves in front and the stallion in the rear — this again could confuse a predator, making the Zebra’s appear to be one large animal.
I don’t believe it’s a strong argument that the Zebra stripes is about camouflage. I believe that the resultant advantage of the stripes helping to break the Zebras silhouette and confusing predators is nothing more than a happy coincidence.
Identification is the next reason given for Zebra having stripes. It has been established that the stripes of a Zebra are as unique to the animal as finger prints are to humans. If we go back in time a few hundred years, we would have seen a great many more animals inhabiting Africa than we do today — authors of diaries and journals from the 1800’s speak of huge herds of antelope (and Zebra) grazing the veld as far as the eye can see.
In this instance one could suppose that with so many of the same species together, Zebra calves would need a way to identify mothers. Zebra do have fantastic eyesight, but this is not the only sense they rely on, their sense of smell is also very keen so it seems unlikely that they would rely only on sight to recognize one another.
Another question to ask is if there is even a need for Zebra to recognize one another. A calf would most likely recognize it’s mother through both visual clues and smell — this hardly seems a good enough reasons to see an entire sub-species develop the black and white striping. Think about horses, they don’t need such extreme visual clues in spite of the fact that 1000’s of years ago great herds roamed.
It seems to me that it’s far to great a leap for an animal species to develop such an extreme patterning like the Zebra just in order to recognize one another, after all, Buffalo, Impala and other antelope species that are just as numerous don’t need stripes for identification.
3. Temperature Regulation
This idea, that the Zebra developed stripes to regulate it’s temperature, I believe is partly correct. The idea is that during the day, the white and black stripes heat at different rates and to different temperatures — kinda like wearing a black t-shirts gets you a lot hotter standing in the sun than a white t-shirt does.
This temperature differentiation causes high pressures and low pressures over the Zebra’s body which causes a breeze to flow about. At first glance is not an unreasonable idea, but if you sit down and start thinking about it, it does kinda fall apart (in my humble opinion).
One of the issues is that any breeze created over the body by the black and white stripes would be interrupted the second the animal started to move. And chances are, the slightest breeze would probably give more relief than the tiny breeze created by the stripes.
On a recent study conducted by Prof. Akesson and others, (read the study here) it was proven that the Zebra stripes had no real effect in temperature regulation. The study did prove that the temperature of the Zebra was moderate in compared to all black or all white skins.
I do believe that the Zebra stripes have been developed as a response to temperature — but not temperature regulation but rather, temperature moderation. My thoughts at the end though.
Right now, the most accepted theory as to why the Zebra has stripes is to do with Ectoparasites, in particular certain species of biting fly. This is not entirely far fetched, the fact is certain biting flies such as the Tsetse fly have caused not only animals deaths but human deaths as well, leading to governments taking extreme measures of carpet bombing land with chemicals such as DDT.
Turns out that because of the structure of the fly eye, they cannot see stripes of a certain width stripes — but this is not true of all biting flies. On top of the that, most biting flies seem to attack the legs where the skin is thinnest and therefore you would expect the legs to have the stripes and not necessarily the rest of the animal.
My argument is the same bug-bear of before, if the biting fly were such a problem a few million years ago, why did only one species of animal combat it by developing stripes?
One argument that may hold weight is that the area in Africa that most biting flies (like the Tsetse fly) are found is central Africa which happens to coincide with the Zebra that have the most distinctive patterning — the stripes are both darker and whiter and more clearly defined.
Personally I found it a weak argument, biting flies do bite Zebra, though perhaps to not the degree they do other animals, but that may be better explained by Zebra population numbers rather than the stripes.
This argument needs to far more comprehensively tested before it can be confirmed or ruled out.
Africa is Pretty Hot
So finally, it’s time for me to put my views forward. And I do stress, they are only my views based on observation as a wildlife guide — I have conducted no studies (wouldn’t even know where to begin) and though I do plan to reach out to some experts to discuss the idea, it’s all an untested hypothesis.
So, my theory is that the Zebra entered into North America from Europe some 6 million years ago. The Zebra stripes we know today, are white on black, that is a white stripe on black skin. It stands to reason that initially then, all Zebra looked similar to horses (as much as they do today) including skin color, which was dark (black or as close to black as is possible).
North America where the species stems from, and Europe where the species spread out to, has a far cooler climate than Africa does. For this reason a darker skin makes sense because you want to absorb as much heat from the day as possible.
As the Zebra moved into the south, the temperature starts to increase which means a dark skin or coat all of a sudden becomes a liability. In order to avoid over-heating during the hot midday sun, Zebra would have to spend their time in the shade and so only graze early morning, late afternoon or even at night — during the periods that predators are most active! Not a practical solution.
Unlike antelope like the Impala, Wildebeest and others, Zebra are not ruminants (they don’t chew the cud) and so they generally spend a great deal more time grazing they do Impala, Nyala or others. This simply means that Zebra don’t get to rest up in the midday shade to chew the cud like ruminants.
Zebra graze all day long, out in the open veld regardless of temperature, they have too in order to get enough fodder to survive. It also makes sense (in a roundabout way) to eat during the heat of the day when predators are least active — a lot harder to keep a watch for predators when your head is down and you are focused on grazing.
So how then do you avoid over-heating thanks to a dark skin during the day? I believe in the KISS principle (keep it simple stupid). So my idea is based on that.
If the Zebra had a dark skin that was preventing it from operating efficiently, then it needs to change. So over time, the Zebra started to develop white stripes in order to deal with Africa’s hot climate.
A study was carried out in 2015 by a group of scientists that showed Zebra in the central to northern sections of Africa had far darker and wider black strips and as you examine the Zebra moving southwards, the stripes become less broad and less distinctive, making the Zebra look far paler, almost (but not quite) white.
This suggests that the Zebra has adapted to the hot climate by having fewer (and less distinctive) black stripes.
For me, this is about temperature moderation. I also believe that in another 5 million years, Zebra in Africa will have lost the stripes and will be mostly white as they adapt to current hot temperatures and of course, future rising temperatures.
I find the subject of animal behavior fascinating but I also think very often us humans tend to over complicate what I think are usual simply reasons for the behavior of animals. But I would love to get your feed back… do you think I’m right? We’re constantly learning about the animals kingdom and this is what makes my work as a wildlife guide so interesting and worthwhile.
My name is Shelldon and I’m the owner of Country and Coastal Touring, based in Durban, South Africa. Wildlife conservation has been as passion of mine since I can remember my Dad and Mom taking us kids on excursions to the Hluhluwe Imfolozi Game Reserve and Kruger National Park all those years ago.
The need to keep people interested and passionate in all things wild has never been more important than right now as pressures from governments and corporations continue to threaten wildlife reserves. Hopefully, through my writings, I’ll be able to contribute to that passion, even if it’s just a little bit.