VSL:SCIENCE // Why cross-breeding makes sense

A mule is a biological hybrid, an offspring of a male donkey and a female horse. According to a new paper, all of this cross-breeding has real benefits: Mules are significantly smarter than either of their parents.

The experiments were like an IQ test for livestock: The animals were shown sets of two food buckets, each marked with a different abstract symbol. In order to gain access to the food, the animals had to correctly match the buckets. Sure enough, the mules were consistently able to identify and remember a greater number of symbols than either horses or donkeys. The scientists speculate that the intelligence of mules results from their genetic diversity. It’s long been recognized that such diversity can produce improved physical characteristics — mules are also stronger than their parents — but this study suggests that diversity also has cognitive benefits. Of course, there’s no reason to think that the hybrid principle is limited to horses and donkeys. In theory, the same logic should also apply to pets — mutts are smarter! — and even people.

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