Zebra stripes are a mystery. Scientists have speculated that they do everything from enabling the equids to evade predators by creating an optical illusion when a herd gallops away to regulating body heat to helping the animals avoid biting flies. But a new team of researchers argues that none of these hypotheses has addressed the marked regional variation in the pattern of striping seen on plains zebras (Equus quagga), which range from southern Ethiopia to eastern South Africa. In some areas, animals in this one species have bold black-and-white stripes over their entire bodies (as in the photo above), whereas elsewhere their marks are fainter and thinner, and some have little to no striping on their legs. Many species, including fruit flies and humans, have similar gradations in their pigmentation because they are adapted to their local environments, the scientists note. Thus, humans living where there is an abundance of ultraviolet light have darker skin, and fruit flies found at high altitude have darker exoskeletons. The researchers propose a similar adaptive reason for the zebras’ varying stripes today in Royal Society Open Science. The scientists quantified the characteristics of stripes on zebras at 16 sites across the animals’ range and examined 29 environmental factors, including temperature, predation, and biting flies, searching for an association. The strongest correlation was between temperature and striping, they report. In areas with the lowest seasonal temperatures, zebras have fewer and fainter stripes. The scientists don’t know why this correlation exists, but suggest that it may be tied to heat regulation or to disease-carrying parasites harbored by tsetse flies. They suspect that multiple biological processes are involved—and require further study.