WHY THE ZEBRA GOT ITS STRIPES

 Photo By Tim Allen

For decades, both adults and children alike have mused over the striking pattern of the zebra’s stripes. Recent research published in the Journal of Experimental Biology has now added further fuel to the debate by revealing an alternative hypothesis to this evolutionary marvel.

Previous attempts to explain the zebra’s unusual pattern are numerous. Some argue that it is used for temperature regulation and for camouflage whilst others say that a large herd moving together confuses predators and makes it harder for them to target individuals. It has also has been suggested that a zebra’s stripes are the equivalent to the human fingerprint and so helps the animals to identify each other. However, the recent research published in Experimental biology has investigated a rather novel trait by examining how differences in skin tone affect the attractiveness of animals to blood sucking horseflies.   

The study was led by Gabor Horvath of Eotvos University, Budapest, and began by studying horses with black, brown or white coats. Horseflies are attracted by ‘flat waves of light’ and Dr Susanne Akesson explains how they found that in the black and brown horses, horizontally polarised light was reflected, making the dark-coloured horses very attractive to flies. Conversely, unpolarised light was found to be reflected from horses with white coats making them less attractive to flies and resulting in less overall disturbance to their demeanour. Once these effects had been established, the scientists then turned their attention to zebras as they were keen to discern whether their stripes elicited a similar behaviour in the flies. Several mocked up models mimicking various black and white patters were produced and the number of flies visiting each model was then counted. The results showed that the pattern that most resembled a zebra attracted the least amount of flies by quite some way, and even attracted less than a plain white model!

Theses experimental findings have opened up a whole new avenue of investigation into why the zebra got its stripes. However, Prof Matthew Cobb concludes that even though the experiment was ‘rigorous and fascinating’, it does not exclude the other hypotheses concerning the origin of zebras' stripes.  More likely, it is down to a combination of evolutionary traits and environmental pressures.

By Tim Allen