Did ancient poison arrows make zebras so skittish?

Thousands and thousands of years of knowing humans to be predators might explain why zebras cannot be domesticated. (Credit: iStockphoto)

Unlike their horse cousins, zebras have never been domesticated—and for good reason: They can be aggressive, panicky, and unpredictable, making them difficult to train.

They also have powerful legs that can carry them at speeds up to 35 mph, and have a kick that can break the jaw of a predator. Those Chuck Norris-like skills are useful when you have lions, cheetahs, and hyenas chasing you down for lunch.

But a new study, published in the Journal of Comparative Psychology, suggests that fear of four-legged carnivores may not be the only explanation for their enduring wildness: they also have a long history of being wary of another kind of predator: people.

For a new study, researchers compared the flight behavior of plains zebras in Africa with that of feral horses in Nevada and California when a human approaches on foot.

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In areas frequented by people, feral horses will allow a researcher to approach much closer than did zebras—waiting until they got about 54 yards away before going into alert mode and an average 18 yards before running away, compared with the zebras’ 68 yards alert distance and 40 yards before fleeing.

Zebras’ wariness may be an evolutionary adaptation that allowed the species to survive hundreds of thousands of years of hunting by humans in Africa. Their 40-yard no-human zone is just outside the effective range of poisoned arrows used by African hunters for at least 24,000 years.

In Central Asia, early horses were hunted initially by archaic humans. Even then, Ice Age weather conditions provided long periods where horses, better adapted to cold climates, saw few human hunters. However, modern humans who replaced them after migrating to Asia from Africa 40,000 to 50,000 years ago were capable hunters of horses. That timeframe was not long enough to evolve an instinctual fear of humans.

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Researchers were surprised to find that in remote areas where people are rarely seen, modern feral horses exhibited as much or more wariness as zebras. Horses showed alert behavior (raising their heads, stopping grazing), on average, when a person got within 218 yards and then moved away when the human was 160 yards away. For the zebras in unpopulated areas, the average distances were 167 yards for an alert response and 115 yards for flight.

“This finding indicates that despite domestication, horses have not lost their keen awareness that an upright, approaching shape viewed from a distance could constitute a predatory threat,” says Richard Coss, professor of psychology at the University of California, Davis.

Source: UC Davis