Evolutionary constraints on equid domestication: Comparison of flight initiation distances of wild horses (Equus caballus ferus) and plains zebras (Equus quagga).

This research article investigates why horses were successfully domesticated, while zebras were not by comparing flight distances of wild horses and zebras in relation to human proximity. The findings suggest that the less pronounced habituation of zebras to humans, possibly influenced by historical hunting, could partly explain their non-domestication.

Introduction and Hypotheses

• The study presents two hypotheses. The ‘human hunting hypothesis’ argues that animals like zebras were hunted by ancestral humans for a long period, leading to a deep-rooted fear of humans, while horses were hunted for a shorter period and hence a less persistent fear.
• The alternative ‘habituation to humans hypothesis’ suggests that zebras can become used to non-threatening humans, if exposed enough. If this is true, there must be other factors contributing to their non-domestication.

Research Method

• The researchers compared the flight initiation distances (FIDs) – the distance at which an animal starts to flee when a human approaches – of wild horses in the United States and plains zebras in Africa (a total of 87 individuals).
• They observed and compared the flight behaviour of both species in areas with low and high human activity, denoted as mean humans/acre as 0.004 and 0.209 respectively.

Findings

• The analysis revealed a significant link between the species and their level of human exposure.
• The average FIDs of horses and zebras in areas of low human exposure were longer compared to areas with high human exposure, but did not differ significantly from each other.
• In high human exposure areas, the FIDs of horses and zebras varied significantly, with zebras maintaining a longer distance.
• The significantly lower FID of horses compared to zebras in high human exposure areas indicates that horses are more tolerant to human proximity than zebras.

Conclusions

• The study concluded that plains zebras are less habituated to humans than horses, possibly explaining their resistance to domestication.
• This lesser degree of habituation toward humans, as suggested by the study, could be an adaptive response of zebras due to their historical hunting by humans.