What is the function of a Zebra's strips? The five leading contenders are: camouflage animals in woods; dazzle big predators into misjudging prey movement; discouraging tabanid and tsetse flies; setting up small convection currents that cool the animal; and, facilitate social interaction. Researchers looked at 20 species or subspecies in the Equus genus: the vividly stripped Zebras, three wild asses with stripped legs; and, eight asses and a wild horse with unstriped coats. The researchers quantified stripiness, or lack thereof, for each of these, using a variety of measures (e.g., number of bars on the neck; intensity of color of leg stripes).
The researchers did not find much of a link between woodsiness and stripe measures, negating the thesis that the stripes help Zebras blend into the light and dark patches in thickets of branches. The stripes were not determined to assist with setting up convection currents, nor disrupting attacks by large predators by motion dazzle. Studies of diets amongst intensely monitored lions also disclaimed the motion dazzle thesis since lions catch an abundance of Zebras. The size of social groups should little relationship with stripes, which cast doubt upon the social interaction thesis.
However, stripes did correlate with geographic regions that had months of weather that favored dense fly populations. Other experiments had shown that flies prefer to land on solid colors instead of stripes, and flies carry four diseases lethal to Equus. Thus, this was deemed the most likely explanation.
But, this explains what function the stripes now serve, not what drove their evolution in ancient climates and ecosystems.
The report can be found at: http://www.nature.com/ncomms/2014/140401/ncomms4535/full/ncomms4535.html.