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How Counting Horses and Reading Dogs Convinced Us Animals Could Think

Before the fin de siècle fad for ‘wonder animals,’ most people assumed creatures were mindless.

Hans selecting answers with his nose. (Photo: Public Domain)

Inky the octopus, who made a crafty escape from his tank in New Zealand a few months ago, joined a continuous stream of headline-grabbing creatures whose antics, especially when captured on video and shared online, tap into a popular fascination with animal minds.

Although metro-riding beavers, militarized dolphins, and their canny ilk seem to pop up almost weekly now, it wasn’t until the early 20th century that psychologists and the general public began seriously considering whether animals had consciousness, emotions, and intelligence. This was due in part to the fin de siècle fad for “wonder animals,” domesticated critters that solved math problems, answered riddles, and discoursed on philosophy, often using a code to communicate with their handlers.

The catalyst for this wonder animal fad was Clever Hans, a mathematically-inclined German horse who gained notoriety in the early 1900s. He could apparently solve math problems–he even did square roots–and carry on simple conversations by tapping his hooves. When Hans started performing for an amazed German public, he amplified a growing interest in animal intelligence that had the potential to transform science and society. Perhaps animals, long regarded as mindless automata, actually had the capacity for reason and language–which meant they might even possess consciousness and something like a soul.

A German crowd gathers to witness Hans’ performance in 1904. (Photo: Public Domain)

Clever Hans was not the first “wonder animal” to astound crowds with apparently human abilities. Magicians and traveling showmen had long trained horses, dogs, and more exotic creatures to perform feats like reading and arithmetic–a “learned English dog” discoursed on ancient Greek poetry in the 1750s, while the French lecturer Perrin employed a “little savant dog” for physics demonstrations a few decades a later. The original sense of “wonder” referred to something that didn’t fit within the divine order of creation–perhaps miraculous, perhaps diabolical. On the stage, wonder animals straddled a line between freak and fraud, but were seldom taken seriously as a scientific phenomenon.

Wilhelm von Osten, a retired high school math instructor in 19th-century Berlin, held a different view. He felt that some animals possessed real intelligence and capacity for abstract thought–not just a love of tasty rewards. Asserting that animal minds were similar to those of human children, he used classroom methods to “teach” rather than “train” his Arabian stallion Hans.

Within a few years, Hans learned to count and then perform basic arithmetic using a system of hoof-taps. In 1904, the New York Times declared that he could “do almost everything but talk,” including telling the time and discriminating between gold and silver coins.

Charles Darwin. (Photo: Library of Congress/LC-DIG-ggbain-03485)

Rather than a wonder or curiosity, von Osten saw this as proof that animals think, learn, and reason, and he intended to make his case to the scientific establishment. The time was ripe for such a radical assertion. Charles Darwin’s theory of evolution was still rippling through the Western world, breaking down the categorical distinction between humans and animals. In 1872, Darwin proposed that emotions like surprise, grief, and pain were part of a shared evolutionary inheritance. This paved the way for the emerging discipline of comparative psychology, and threatened humans’ special status as the only earthly creatures with thoughts and feelings.

Another factor that primed audiences for a serious encounter with the animal minds was the rise of pet ownership. People had long used animals for food and labor, but only the elite had the luxury of keeping pets as companions. This began to change in the 18th and 19th centuries, when pets became a middle-class trend. As people formed emotional attachments to their furry friends, they observed qualities like loyalty, love, and intelligence in dogs and, to a lesser extent, cats.

Stories about remarkable pets proliferated in the press. The “incredible journey” tale, in which devoted pets travel vast distances to reunite with their masters, originated around this time. Its heroes included Victor Hugo’s poodle, who supposedly trekked from Moscow back to Paris.

Hans and his original trainer, Wilhelm von Osten, pictured with the chalkboard that von Osten used to spell out math problems for Hans to solve. (Photo: Public Domain)

Pet owners like Paula Moekel of Mannheim, Germany, invited scientists to confirm their ambitious claims. Moekel believed that her terrier Rolf could discourse on philosophy in multiple languages. However, when investigators arrived they had an unsatisfactory experience–Rolf suffered from seizures, and was unable to show off for his guests. This cycle repeated in numerous cases: wonder animals, much like human psychic mediums, could rarely perform under the scrutiny of a skeptical audience.

Clever Hans, however, was not just any coddled pet. Von Osten insisted on the scientific importance of the phenomenon, and invited psychologists and physiologists to examine his equine pupil under controlled conditions. A committee of experts from Berlin scrutinized Hans in 1904 and concluded that his accomplishments were genuine–they ruled out the use of secret signals by von Osten. One of these experts, however, was not entirely satisfied, and persisted in a solo investigation. 

Psychologist Oscar Pfungst’s investigation of Clever Hans charted the horse’s hoof-taps and correlated them precisely with the unconscious physical cues of his questioners. (Photo: Public Domain)

The dissenter, a young psychologist named Oscar Pfungst, came out with a devastating critique of Hans and von Osten in 1907. He found that Hans could not produce correct answers if he couldn’t see his human questioner or an audience member. Suspecting that the horse relied on physical gestures, Pfungst experimented with shrugging his shoulders or changing his posture during tests–and his subtle movements ruined Hans’ performance.

Like so many other wonder animals, the horse merely “read” human cues. Previous investigators had refused to believe that they could send such cues unintentionally, but Pfungst made a firm case, carefully correlating Hans’ hoof taps with the twitches and fidgeting of his handlers.

The legacy of Hans and Pfungst lives on today in psychology textbooks. The “Clever Hans effect” is when an experimenter elicits correct answers from an animal subject by giving the subject unconscious cues, creating a persuasive illusion of intelligent thought. This is where the story traditionally stops, with the debunking of Clever Hans and the moral that psychologists must rule out unconscious experimenter bias in their studies.

Munito, a “chien savant” of early-19th-century Paris, gained a reputation as the “Newton of the canine race,” but his performance was widely attributed to trickery. (Photo: Public Domain)

This was certainly not the end of the line for discussions of animal intelligence, however. Despite scientists’ best efforts to curtail it, popular interest in thinking animals remained vigorous throughout the 20th century. The Hans phenomenon inspired countless imitators, including “Lady Wonder,” a mare purported to have telepathic powers. During World War II, Nazi scientists tried training dogs to read and speak in code, hoping to find military applications for these talents. Even within professional psychology there were supporters of animal intelligence (among them Margaret Floy Washburn, the first American woman to receive a doctorate in psychology), but their work was often minimized or dismissed.

Over the past thirty years, though, the old guard of psychology–which saw human mental faculties as distinct from those of animals–has given way to outspoken researchers like primatologist Frans de Waal, who place humans and animals on a mental continuum. Modern celebrity animals like John W. Pilley’s dog Chaser and Irene Pepperberg’s parrot Alex, who both appear to understand thousands of words and basic grammatical structures, may be the heirs of Clever Hans, but their handlers’ scientific respectability makes them harder to dismiss.

Hans’ next owner, German merchant Karl Krall, with two later horses, Zarif and Muhamed, who surpassed Hans in their educational attainments. (Photo: Public Domain)

Indeed, Hans himself was never as marginal as many textbooks made him seem. Von Osten, who died in 1909 a disappointed man, might be pleased to see that animal intelligence has made a comeback in psychology–scientists are even returning to calculating horses, this time to study how animals make decisions that aid their survival, rather than whether they understand math.

The fate of Clever Hans raises questions about how we define and value intelligence. What, after all, makes figuring square roots more important than reading body language with incredible acuity? Recent work in human psychology is revealing how unconscious cues and impulses actually determine most people’s everyday decision-making.

In the past, we’ve called animals “clever” when they conform to our ideal of rational, calculating intellect–even when we can’t uphold that ideal ourselves. Perhaps neither humans nor horses are as clever as we might like to believe.