It turns out that zebras are not referees at the horse games as many children may think. In fact, the patterns of the black and white stripes on a zebra are an evolutionary adaptation that has benefits for the animals. Several different and plausible hypotheses have been proposed for the reason behind the stripes ever since Charles Darwin first came on the scene. Even he puzzled over the significance of the stripes. Over the years, different scientists have suggested the stripes could either be to help camouflage the zebras or confuse predators. Other ideas were to lower body temperature, repel insects, or to help them socialize with one another.
The Evolutionary Advantage of Stripes
A study, done by Tim Caro and his team from the University of California, Davis, pitted all of these hypotheses against each other and studied the statistics and data gathered. Remarkably, the statistical analysis showed over and over again that the most likely explanation for the stripes was to keep flies from biting the zebras. Although the statistical research is sound, many scientists are careful about declaring that hypothesis the winner until more specific research can be done.
So why would stripes be able to keep the flies from biting the zebras? The pattern of the stripes seems to be a deterrent to the flies possibly due to the make up of the flies' eyes. Flies have a set of compound eyes, just like humans do, but the way they see out of them is much different.
Most species of flies can detect motion, shapes, and even color. However, they do not use cones and rods in their eyes. Instead, they evolved small individual visual receptors called ommatidia. Each compound eye of the fly has thousands of these ommatidia that create a very broad field of vision for the fly.
Another difference between human and fly eyes is that our eyes are attached to muscles that can move our eyes. That allows us to be able to focus as we look around. A fly's eye is stationary and cannot move. Instead, each ommatidium collects and processes information from different directions. This means the fly is seeing in several different directions at once and its brain is processing all of this information at the same time.
The striped pattern of a zebra's coat is a sort of optical illusion to the fly's eye because of its inability to focus and see the pattern. It is hypothesized that the fly either misinterprets the stripes as different individuals, or it is a sort of depth perception issue where the flies simply just miss the zebra as they try to feast on it.
With the new information from the team at the University of California, Davis, it may be possible for other researchers in the field to experiment and get more information about this very advantageous adaptation for zebras and why it works to keep the flies at bay. As stated above, however, many scientists in the field are hesitant to back this research. There are many other hypotheses as to why zebras have stripes, and there may be several contributing factors as to why zebras have stripes. Just like several human traits are controlled by multiple genes, zebra stripes may be the equivalent for the zebra species. There may just be more than one reason as to why the zebras evolved stripes and not having flies biting them may just be one of them (or a pleasant side effect of the real reason).