Why zebras have black and white stripes is a question that has intrigued scientists and spectators for centuries. A research team led by UC Davis, has now examined this riddle (in a very systematic way).
Many hypotheses for zebra stripes have been proposed since Alfred Russel Wallace and Charles Darwin debated the problem 120 years ago. These include:
- A form of camouflage
- Disrupting predatory attack by visually confusing carnivores
- A mechanism of heat management
- Having a social function
- Avoiding ectoparasite attack, such as from biting flies
After analyzing the five hypotheses, the scientists ruled out all but one: avoiding blood-sucking flies. The scientists found that biting flies (such as horseflies and tsetse flies) are the evolutionary driver for zebra stripes.
Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies.
Yet in science, one solved riddle begets another: Why do biting flies avoid striped surfaces?