London, Aug 1: When it comes to being smart, mules are far ahead of their parent species in the ‘intelligent’ race, says a new research by scientists at the University of Sussex in Brighton.

Leanne Proops at the University of Sussex in Brighton, UK, tested the learning skills of horses, donkeys and mules in a bid to assess their cognitive abilities.

Six of each animal were shown sets of two food buckets, each marked with a different symbol. In order to gain access to the food, the animals had to pick the correct bucket.

The mules learned to discriminate between more pairs of symbols than the horses or donkeys, and did so more consistently.

According to Proops, the increased intelligence in the mule is a result of hybrid vigour, where the best genes of the parent species "mix and match" to produce hybrids with superior traits, reports New Scientist.

While this mechanism gives mules greater height and endurance than either parent, this is the first study to show that hybrid vigour is able to improve cognitive function, too.

Although mules are physically robust and smart, they are also sterile, notes Ben Fitzpatrick of the University of Tennessee at Knoxville.

So unfortunately, in evolutionary terms, this increased intelligence is a gift that cannot be passed on. (ANI)