My favourite answer to this question comes from an ancient San Bushmen story:
Many generations ago, in the heart of Africa, a baboon sat guarding the one and only waterhole for many miles. He was a nasty baboon. A baboon that only allowed certain animals to come and drink water from this watering hole, which he claimed belonged to him. Being scorching hot, the animals of the savannah became very thirsty and would regularly come and try to drink some water. Often they would get chased away.
The baboon, being the cunning and intelligent chap that he is, knew that at night the temperatures in the Savannah can drop dramatically. To keep himself warm, he had made a fire that he kept burning through the day and night.
One day, the zebra came along to the baboon’s watering hole to have some water. In those days, zebra were a pure white colour. The baboon was particularly grumpy and tried to chase the zebra away. They had a huge fight, and zebra kicked baboon with all his might, sending him flying up onto a rocky outcrop. The baboon landed with such a thud that the skin on his backside was torn off completely. To this day, the baboon still has a bare, pink bottom!
In the fight, the zebra tripped over backwards and fell into the burning fire of the baboon. He sent logs flying into the air, some of which landed on him, burning black lines into his coat all over his body. The logs burnt so badly that the zebra yelped in terror and sprinted all the way into the open plains of the savannah to try cool off. To this day, the zebra and his family have black lines on their bodies and are found in the open plains of Africa.
Some people do not take this San story as the truth though, and have put forward some alternate theories…
The black and white stripes may serve to help zebra blend in with the long grass in their environment. This is not widely accepted as often zebra are found in open areas and can be seen (or smelt by predators) from a long distance. It is not necessarily incorrect though as if you look at a zebra on the edge of a thicket line in the evening (when as humans, we are using the light sensitive rod cells in our eyes and are seeing in grayscale) you will struggle to focus on an individual. This may be the same for predators who see predominantly in black and white.
2. Confusion Tactic
As a gregarious or herd species, zebra will stick together when fleeing from a threat. In doing so, the stripes of each individual cross over with the stripes of other individuals and it is difficult to distinguish one individual from the next. This is particularly true through the black and white view of a predator. Predators can be thrown off by this as they prefer to single out one animal to follow in a herd.
3. Thermoregulation (keeping cool)
Studies have shown that a temperature gradient is formed between the black and white stripes on a zebra’s body. Zebras in warm climates (central Africa) have more stripes than species in cooler climates (southern Africa). More heat is absorbed by the black stripes than the white ones, creating a tiny pressure gradient across the body, causing small eddies of wind to blow between the stripes. This could be an adaption for keeping cool in the harsh sun of the savannah. However, this still needs to be tested in the field!
4. Fly Deterrent
It has been shown that flies are more attracted to single colours rather than stripes. Zebras patterns may be in place to dissuade biting flies from their skin; an adaption to lesser parasite loads. This is particularly true for areas in central Africa where climates are more humid, year round, and the prevalence of biting and disease carrying flies (like tsetse flies) is higher than in southern Africa.
5. Individual Recognition
Each zebra has a unique stripe pattern, like our fingerprints. Although at first not that obvious to us humans, take a closer look next time and you will notice wonderful, unique patterns on zebras’ bodies. This may help in herd cohesion; mother-foal recognition and/or mate choice, as a few examples.
Whatever you may believe, the reality is that we actually don’t know why zebras really have stripes… It’s a pity we can’t ask their opinion. During a discussion on this topic with a guest recently, I found the closest solution yet:
“Pete, it’s simple! The reason zebra have stripes is this: imagine they had spots? How silly would that look!”