How the Striped Zebra Evolved

An old African Legend tells of a young zebra and baboon arguing about getting a drink at a waterhole. A baboon had declared this waterhole his property and guarded it fiercely. Sitting by his fire, the baboon forbade the zebra from drinking and combat ensued. With a mighty kick, the zebra sent the baboon flying. He landed on his seat, creating the bare patch on his rump seen in baboons today. The zebra fell back through the baboon’s fire which scorched him leaving black stripes across his white fur. In shock, he ran to the plains where, with their striped coats, zebras have lived ever since.

Although this is a charming explanation for zebra stripes, evolutionary biology tends to work in much more practical ways. Characteristics develop within a species or group because they provide a survival advantage. In the case of zebra stripes, a number of survival advantages seem to have played an evolutionary role:

1. Cooling mechanism – the alternating color pattern deflects up to 70 percent of the heat hitting the zebra
2. Identification in the herd – their unique stripes enable zebras to tell each other apart promoting their social behavior of herding
3. Camouflage – because they travel together in large herds, it is believed the mass of stripes creates the optical illusion of a single large blob intimidating predators. Lions and hyenas believe they are seeing one larger creature; thus, they are less likely to attack.
4. Reducing parasitism from horseflies – this is the most recent theory regarding the evolutionary pressure of stripe development in zebras.

• The plains of Africa are also home to many parasites including the blood-sucking horse fly. I have been bitten on our farm several times and can attest to the nasty bite resulting in a section of skin also missing.
• Horseflies also carry disease and distract the animals from their grazing activities and possibly from detecting predators. The blood-sucking female flies are attracted to linearly polarized light reflected from the hides of grazing animals.
• Gabor Horvath and his colleagues from Hungary and Sweden have determined that the narrow stripe pattern of zebras reduces light reflection from the zebras’ hides, reducing the number of nasty bites from blood-sucking insects; therefore, reducing disease and distraction from eating and noticing predators.

Ancient people have always tried to explain events and the world around them according to their level of comprehension at the time. In the last century, humankind's understanding of genetic processes within the cell and within communities of organisms has skyrocketed. Local myths and legends give us a glimpse into the kind of curiosity already present in humans which would gradually lead to all discoveries which would follow. Zebras did not get their stripes by an ancestor who fell into a fire, but humans were curious as to why they had stripes to begin with.

1. We now understand that environment and experience help to shape genetic expression. As is true of the zebra, a number of environmental influences can shape the expression of a characteristic.
2. For the zebra the following factors were important in the development of their stripes:

• the need to conceal themselves from predators,
• keeping themselves cool in the hot African plains,
• herd behaviour and
• reduction of parasitism.