Zebras’ wariness of humans may have been an evolutionary adaptation to keep them beyond the range of poisonous arrows used by African hunters for at least 24,000 years, researchers suggest.
They suggest this caution may have allowed the species to survive hundreds of thousands of years of hunting by humans in Africa.
Unlike their horse cousins, zebras have never been domesticated. 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 35mph, and have a kick that can break the jaw of a predator.
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 people.
Researchers compared the flight behavior of plains zebras in Africa with that of feral horses in Nevada and California when approach by a human on foot.
In areas frequented by people, feral horses will allow a researcher to approach much closer than did zebras.
Wild horses waited until the researcher got about 54 yards away before going into alert mode and an average of 18 yards before running away.
Zebras, on the other hand, were on alert at 68 yards fled at 40 yards, which is just outside the effective range of poisoned arrows used by African hunters.
In Central Asia, early horses were hunted initially by ancient humans. Even then, Ice Age weather conditions provided long periods where horses, better adapted to cold climates, saw few human hunters.
However, the modern humans who replaced them after migrating to Asia from Africa 40,000 to 50,000 years ago were capable hunters of horses. However, that time-frame was not long enough to evolve an instinctual fear of humans.
Researchers were surprised to find that in remote areas where people were rarely seen, modern feral horses showed as much, or even more, wariness than zebras.
Horses showed alert behavior – raising their heads and stopping grazing – when a person got within 218 yards, on average, and then moved away when the human was 160 yards away. For 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.
Evolutionary Constraints on Equid Domestication: Comparison of Flight Initiation Distances of Wild Horses (Equus caballus ferus) and Plains Zebras (Equus quagga).
Brubaker, Alexali S.; Coss, Richard G.
Journal of Comparative Psychology, Sep 7 , 2015.
The abstract can be read here.
Original press material was published under a Creative Commons License.