Clever Hans: The Genius Horse

In the late nineteenth century, society had a heightened interested in animal intelligence spurred on by Charles Darwin’s then recent writings. A German man by the name of William Von Osten took particular interest. Von Osten subscribed to the school of thought that the human race greatly underestimated the inherent intelligence of animals.

To test his hypothesis, Von Osten conducted experiments on a bear, several cats, and finally a horse. After receiving nothing to show but cuts and scratches from the bear and cats, Von Osten had a breakthrough with his horse. Encouraged by his early success Von Osten went on to create a strict regimen of tutoring with his horse, affectionately known as Hans. Eventually Hans was able to answer questions written on a blackboard and spoken by Von Osten with amazing accuracy.

After much practice, Hans the horse went on tour around Germany in 1891 and became known as Clever Hans. Von Osten entered Hans in fairs and provided free exhibitions to astonished audiences. Von Osten would even field unscripted questions from skeptical onlookers, which Clever Hans could answer without effort. Under close observation Clever Hans actually answered questions correctly about 89% of the time. Pretty impressive for a horse.

Hans eventually went on to find answers to simple fractions and square roots. To answer questions not involving numbers Hans would tap once for “A”, twice for “B”, up to 26 for “Z”. Hans would even spell out audience names using this method.

A horse that could answer arithmetic questions on the level of an average 14 year old certainly drew its skeptics. Von Osten was happy to provide Hans for testing, as he had nothing to hide. The German Department of Education put together a commission known appropriately as the Hans Commission. The group consisted of a zoologist, a veterinarian, a psychologist, and several teachers. Regardless of the questions the commission presented Clever Hans, Hans was able to correctly answer. The commission went on to conclude, as far as they were concerned, Hans’ talents were genuine and no trickery was involved as first suspected.

Not satisfied with this conclusion, skeptic psychologist Oskar Pfungst had some innovative ideas to further test Hans. Pfungst started by removing as much stimuli as possible, by putting the horse indoors in a controlled environment. After that yielded no change in the horse’s apparent intellect, Pfungst tried moving Von Osten and the other scientists out of Hans’ line of sight. Interestingly enough, Hans seemed to lose his talents immediately. They also left Von Osten in the horse’s view, but hid the question from Von Osten. Again, Hans fell short. Pfungst had another test to perform. For this one, Pfungst put a scientist in view of the horse, but not Von Osten himself. Strangely enough, Hans had no problem answering questions now. But when the scientist wasn’t aware of the question being posed, Hans was not so clever anymore.

Pfungst now had a hunch and switched from observing the behavior of Hans, to observing the behavior of Hans and whomever Hans could see. Pfungst eventually noticed that Hans could seemingly read hidden body cues and detect what the appropriate answer was. Upon further investigation, it was found that whoever was around Hans would inadvertently tense up as Hans neared the correct amount of taps. Once the correct amounts of taps were made, the observer would relax and Hans would know to stop tapping.

Pfungst went on to discover that Hans could read faces for these subtle clues of tension, along with sensing a change in the observer’s heartbeat. Even when the observers were aware of this discovery, they could not hide it from Hans. After further study Pfungst concluded that although Hans was no mathematical genius, and in reality knew no math, Hans had another talent.

The conclusion prompted further study into the interaction of animals and humans, and made significant changes to the way studies involving animals were done. It was discovered that many species of animals have the ability to read these subtle body cues like Clever Hans. As a result, the term “Clever Hans Effect” is used during research to refer to this phenomenon. It is taken into account to help researchers obtain more accurate results from research using animals and even human subjects.

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