Horses, donkeys, onagers and zebras

An explanation

The species described as a "wild ass" in the bible should correctly be called an onager, an Asian species intermediate between donkeys and true horses [3].
Domestic donkeys are descended from African wild asses, which have larger ears than onagers, and possess a dark stripe across the shoulders and along the spine. These markings are like a highly simplified version of the stripes of zebras. Darwin observed that horses (and onagers) occasionally had a spinal stripe, one or more shoulder bars, and or stripes on the legs. The markings are often seen in foals, disappearing with age. He also noted donkeys lacking shoulder bars. In his own words:" For myself, I venture confidently to look back thousands on thousands of generations, and see an animal striped like a zebra, but otherwise very differently constructed, the common parent of our domestic horse,.....of the ass, the hemionus [onager], quagga, and zebra. [7]
Stephen Jay Gould has developed this idea further, suggesting that the three surviving species of zebra may be more closely related to asses and horses than to each other [8]. I think that it is significant that the shoulder stripe is a variable genetic trait. An onager foal might be born with a shoulder stripe, even though its parents lacked this pattern (onagers were occasionally domesticated in the past [3]), likewise, a donkey might be born unstriped, or lose its cross later in life. Such phenomena could give rise to the legend that the cross markings are a sign of divine goodwill. Topsell[14] seems to recognise that wild asses are a distinct species from true asses, but confuses them with zebras, unicorns, oryx and rhino. Oryx, onager and rhino may all have played a part in the unicorn legend (see the White Goddess page for more on this)[back]

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