Why do zebras have stripes?

The zebra is the most conspicuously dressed large mammal on Earth, a grazing animal on open plains wearing high-contrast stripes visible from a distance. Darwin and Wallace disagreed about the point of it in the 1870s, and the disagreement never really closed; it just accumulated better experiments. The stripes are clearly doing something, since evolution rarely maintains anything this loud for free. The something is still being pinned down.

Why it matters

This entry is small on purpose, and it earns its shelf. The zebra is a clean test of whether evolutionary biology can deliver verdicts about function, because the hypotheses make different predictions and most are testable. It is also a caution about obvious answers. Camouflage, the schoolbook explanation, has fared badly: lions and hyenas cannot resolve the stripes at hunting distances in the light conditions that matter, so the pattern likely is not hiding zebras from anything that eats them.

What has been tried

The candidate functions have been raced against each other. Predator confusion, the idea that stripes dazzle a charging lion or make one zebra hard to isolate from the herd, has little direct support and some evidence against it. Thermoregulation, stripes as self-cooling stripes of differential airflow, has been tested with instrumented hides and drone surveys with mixed and mostly negative results. Social functions, stripes as identity badges, explain neither the pattern’s cost nor its geography. The fly hypothesis has pulled ahead on evidence. Comparative studies across equid species and populations found striping strongest exactly where biting flies, which carry diseases lethal to horses, are worst. Experiments with striped and plain coats on real horses show the flies approach both equally but fail to land properly on stripes, aborting or crashing their final approach. Painted stripe patterns measurably cut landings.

Where the edge is

Why flies cannot land on stripes is unknown; something about the pattern disrupts their visual control of approach, and the mechanism is untested at the level of fly neuroscience. Nor is it settled why zebras evolved this defense while antelope grazing the same fly-ridden plains did not, whether thinner-skinned or shorter-haired animals needed it more, or whether the stripes carry secondary benefits once evolved. The leading hypothesis, in other words, has opened a fresh set of questions underneath itself.

What would count as an answer

The fly-vision mechanism demonstrated directly, plus a comparative account explaining who gets stripes and who does not. The question will retire in stages, and this entry will track each one.