There is continued debate over both the merits of individual hypotheses and the likelihood of stripes having arisen via a single driver vs. The hypotheses suggest various ways in which stripes may provide a social function (species or individual recognition or social cohesion 1, 4), a temperature-regulation benefit 5, 6, an anti-predator effect 7, 8, or an anti-parasite effect 9, 10. Scientists have proposed and investigated several possible explanations for the evolution of zebra stripes (reviewed in 3). So, striping presents an ideal evolutionary puzzle: a trait so refined it seems it must be “for” something, but one that confers no clear advantage upon its bearers and imposes apparent costs (conspicuousness) that cannot be explained in Zahavian terms. Stripes are clearly not aposematic warning signals, nor do they provide camouflage in either the woodland or savannah habitats common across zebra ranges 1, 2. Unlike many conspicuous visual traits, striped pelage is expressed with comparable intensity in both sexes and is thus unlikely to have arisen through sexual selection alone (although in plains zebras, Equus quagga, males have stripes closer to true black than females). However, the utility of a complete coat of densely packed, starkly contrasting black-and-white stripes is not immediately apparent. The trait is rare, conspicuous, and intensely expressed, and thus appears to beg an adaptationist explanation. The evolutionary origins of zebra stripes have been investigated-and debated-for centuries. Our findings confirm that zebra stripes repel biting flies under naturalistic conditions and do so at close range (suggesting that several of the mechanisms hypothesized to operate at a distance are unnecessary for the fly-repulsion effect) but indicate that interspecific variation in stripe width is associated with selection pressures other than biting flies. In paired-choice field experiments in a Kenyan savannah, we found that hungry Stomoxys flies released in an enclosure strongly preferred to land on uniform tan impala pelts over striped zebra pelts but exhibited no preference between the pelts of the zebra species with the widest stripes and the narrowest stripes. In addition, the complex visual features of real zebra pelage and the natural range of stripe widths have been largely left out of experimental designs. Myriad hypotheses have been suggested, but few experiments have helped narrow the field of possible explanations. While this effect is well-established, the mechanism behind it remains elusive. Former service personnel are eligible for reserves and in many cases can enlist at same grade held at time of discharge."įormat 1 photographic print :b&w 26 x 21 cm.The best-supported hypothesis for why zebras have stripes is that stripes repel biting flies. Kokensparger gained rating by enlisting in Air Reserve at Van Nuys Air Reserve Center. Please see the Ordering & Use page at for additional information.ĭescription Photograph caption dated Apreads, "Jesse James Kokensparger of Pacoima proudly holds set of staff sergeant stripes for Orlanda Munyon, Miss Panorama City, to see. Images available for reproduction and use. Made accessible through a grant from the John Randolph Haynes and Dora Haynes Foundation and Photo FriendsĬollection Los Angeles Public Library Photo Collection Institute of Museum and Library Services under the provisions of the Library Services and Technology Act, administered in California by the State Librarian Title Admires new stripes Alternative Title Valley Times Photo CollectionĬontributor This project was supported in whole or in part by the U.S.
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