We’ve always believed that language is what sets humans apart from every other creature on Earth. But then came Koko — a gorilla who proved otherwise. She learned more than 1,000 signs and used them to ask for kittens, crack jokes, and even tell little lies. She could show love, sadness, and joy in ways no one thought possible. But Koko’s most shocking words weren’t about food or play. They were about humans — and what she said about us was so unsettling, it may change the way you see yourself forever.
In October 1978, National Geographic published an arresting cover: a female lowland gorilla, camera in hand, studying her own reflection. Her name was Koko, and she wasn’t posing.
The image came from photographer Ronald H. Cohn, who had spent years documenting Koko’s progress at Stanford University. It showed something quietly revolutionary — an animal observing herself.
That photograph introduced the world to a gorilla who could use more than a thousand signs. But long before the fame came the fragile beginning of her story.
Koko was born on July 4, 1971, at the San Francisco Zoo. Her Japanese name, Hanabiko, meant “Fireworks Child.” It matched both her birth date and her spirited temperament.
At six months old, she developed viral pneumonia — a severe respiratory infection that nearly killed her. Weak and separated from her mother, she was transferred to the zoo nursery for round-the-clock care.
There, surrounded by human voices instead of gorilla calls, Koko recovered slowly. Her exposure to people during that isolation would later make her uniquely receptive to language.
Francine “Penny” Patterson was a Stanford graduate student studying developmental psychology. In 1972, she met Koko while volunteering at the zoo and saw what others hadn’t: alertness, curiosity, focus.
Patterson proposed using American Sign Language (ASL) to communicate with her. The idea was radical — no gorilla had ever been part of a human language study before.
Her proposal became Project Koko. The experiment would move from the zoo to Stanford’s Psychology Department. One student and one young gorilla were about to redefine intelligence.
Training began in July 1972. For 10–20 hours a week, Koko worked with Patterson and fluent ASL users. They used molding — shaping her hands — and imitation to teach basic words.
Within months, Koko learned her first independent sign: eat. Next came drink, then more. Each gesture was recorded, witnessed, and reviewed before being accepted as genuine communication.
By her third birthday, Koko had mastered about 100 signs. For a gorilla with no precedent, that was extraordinary progress, and scientists were only beginning to understand what it meant.
However, before Koko, Patterson learned about Washoe, a female chimpanzee born in 1965 and raised in Nevada by researchers Allen and Beatrix Gardner. Washoe became the first non-human to learn American Sign Language.
By 1969, she had acquired over 130 signs, including words like more, open, and you me go out. Unlike imitation experiments before her, Washoe used signs spontaneously, even combining them.
Her success proved that apes could associate symbols with meaning. But what stunned scientists wasn’t her vocabulary — it was her ability to express emotion. That would change everything for Koko’s future.
Washoe’s team noticed that her signs weren’t mechanical. When happy, she laughed; when corrected, she sulked. Her expressions mirrored human emotion in tone and timing.
In 1982, a volunteer named Kat Beach told Washoe she had miscarried. Washoe paused, then traced a line down her cheek — the sign for cry. Then, before Kat left, she signed “Please person hug.” It seemed like she didn’t want Kat to leave without being comforted.
Chimpanzees don’t cry tears, but Washoe understood the gesture’s meaning. It was empathy made visible, and it raised a question no scientist could comfortably ignore: what if language wasn’t uniquely human?
Penny Patterson followed Washoe’s work closely while preparing her own study. Washoe proved that apes could use symbols; Patterson wanted to see if gorillas could attach those symbols to emotion.
Her hypothesis was straightforward but risky: if Koko could learn sign language, it might reveal a shared foundation between human and animal thought. The challenge was finding a method rigorous enough to convince skeptics.
With Washoe’s data as a model, Patterson established strict criteria for every word Koko learned — documentation, repetition, and appropriate use. The scientific burden would be heavy, but Koko was an exceptional student.
Koko’s training schedule resembled that of a full-time student. For up to 20 hours a week, she practiced signs for familiar objects: ball, flower, toy, drink.
The teaching relied on two methods. In “molding,” instructors shaped Koko’s hands into the correct ASL form. In “imitation,” they demonstrated signs repeatedly until Koko copied them herself.
Rewards were small — fruit, candy, affection — but the breakthrough moments were enormous. When she first signed eat without prompting, the team realized she wasn’t just imitating. She was really communicating! But the scientific method needs certainty.
To guard against bias, Patterson imposed verification rules rarely used in animal-language studies. Each sign had to meet three criteria before being accepted into Koko’s recognized vocabulary.
First, it had to be witnessed by two independent observers. Second, it had to appear spontaneously on at least half the days in a given month. Third, it had to be used contextually correct.
The protocol was tedious, but necessary. Language research had been plagued by claims of mimicry and suggestion. But Patterson was determined that Koko’s intelligence would stand up to scrutiny.
By 1974, after just two years of training, Koko knew more than 100 verified signs and used several hundred others informally. She signed food, drink, love, and me Koko.
Her progress was charted like a child’s developmental record — one that sometimes outpaced early human benchmarks. By age three and a half, her comprehension resembled that of a two-year-old child.
For researchers, the implications were staggering. If a gorilla could reach toddler-level cognition through sign language, where exactly did human uniqueness begin — and end?
As her skills grew, Koko began altering certain ASL signs to fit her anatomy. Gorillas have shorter thumbs and broader palms, making some handshapes physically impossible.
To adapt, she created her own modifications. Her name sign, for instance, became a soft pat on the shoulder — easier than forming the ASL letter “K.”
Over time, these adaptations evolved into a dialect Patterson called Gorilla Sign Language. Koko wasn’t just learning a language; she was reshaping it for her species. And it gets even better!
By the age of five, Koko used roughly 500–600 signs regularly and understood more than a thousand spoken English words. Her IQ, tested through adapted human scales, was estimated at around 85.
Not only can she label objects, but she can also form sentences, request items, and express preferences. When asked what she wanted for her birthday, she signed cat.
That request would change her public image forever. But first, a new presence was about to enter her world — one who would challenge and deepen her understanding of language.
In 1976, a young male gorilla named Michael joined Koko’s household. Like her, he had been taken from his mother as an infant and raised in captivity.
At first, the arrangement didn’t go smoothly. Koko resisted sharing attention with another gorilla. Their play often turned into wrestling — displays of dominance more than affection.
But months later, something shifted. Surprisingly, the two began to mimic each other’s signs! Soon, researchers discovered something remarkable out of their shared understanding.
Penny Patterson began teaching Michael American Sign Language the same way she had taught Koko. Within a year, he had mastered about twenty signs, including food, love, and play.
What surprised Patterson wasn’t his speed, but his collaboration. When Michael struggled with a sign, Koko often demonstrated it first! For the first time, a rare sight, one ape was teaching another.
Their shared learning sessions revealed that language could spread socially among gorillas. If one could learn to sign, perhaps others could too — a revelation no lab had ever recorded before.
By 1978, Koko and Michael could exchange simple dialogues: signs for good morning, food now, or play chase. They even invented nicknames for their caretakers.
When Michael signed “Ingrid” and “Karen” — the names of two researchers — he had learned them from Koko, not humans. It was linguistic transfer, a critical indicator of comprehension.
But like any other language, Gorilla signs were not flawless. They sometimes overgeneralized, using one sign for multiple meanings. When Koko signed straw, she might mean a pen, a cigarette, or even a car antenna. And things like these fueled critics to ask more questions.
Despite the breakthroughs, critics demanded harder evidence. How could anyone know the gorillas truly understood their signs and weren’t simply imitating human cues for rewards?
The debate echoed an older controversy in animal psychology — one involving a horse named Clever Hans. Like Koko, his story fascinated the public and frustrated scientists.
To prove Koko’s intelligence was genuine, Patterson would need an experiment that eliminated all human influence — even her own.
At the turn of the 20th century, a horse in Germany named Clever Hans captivated crowds by seemingly solving arithmetic problems. His trainer, Wilhelm von Osten, claimed Hans could count.
When asked, “What’s six plus fifteen?” Hans would tap his hoof twenty-one times, stopping precisely at the right number — and earning sugar cubes in return.
But scientists discovered that Hans wasn’t doing math at all. He was reading tiny facial cues from humans, stopping when they looked satisfied. His intelligence was real, but well… misunderstood.
To avoid the “Clever Hans effect,” Koko’s team designed double-blind experiments. In one, a researcher placed an object in a box visible only to Koko, not to another tester.
The second tester then asked Koko, “What is in the box?” Without visual cues or prior knowledge, the only correct answers could come from Koko herself.
Out of fifty trials, she identified thirty-one correctly — a 62% success rate! Perfection wasn’t the goal of the test, but the result was far better than chance. The evidence was building. And her errors? It revealed something far more important.
Koko sometimes confused similar categories — calling candy cracker or signing key box when impatient. However, the mistakes exhibited patterns consistent with genuine cognitive processing.
She didn’t always cooperate. Some days, she ignored questions and changed subjects entirely, signing ‘key open’ or ‘play me’. Her refusals looked familiar to anyone who’s ever taught a toddler.
The results confirmed it: Koko wasn’t simply guessing. She knew what to choose. Her signs carried intention, not performance, and that distinction would later reveal a shocking truth about Koko’s observation of humans.
By now, language had become part of daily life for both Koko and Michael. Their vocabulary included not only nouns and verbs, but also emotions — love, sad, cry, angry.
When asked how she felt, Koko often signed fine, good, or sometimes sleepy. The gestures came easily, as if emotion and communication were naturally linked.
But emotions in captivity could also be heavy. Michael, in particular, carried a memory that would haunt his signing for years.
When researchers once asked Michael about his mother, he signed trouble, cry, bad, and then mimed a shooting motion. The meaning was unmistakable.
Michael had been captured in Cameroon, where poachers killed adult gorillas for bushmeat and sold their infants to collectors. He had likely witnessed his mother’s horrifying death.
The memory explained his volatility and deep attachment to Koko. For the scientists watching, it was a devastating confirmation that trauma is not only for humans. Animals experience it, too. But aside from communicating painful memories, Koko developed a skill that was more inherent to humans.
Koko’s emotional intelligence surfaced in unexpected ways. During a 1985 interview with National Geographic writer Cynthia Gorney, Koko abruptly called her a “toilet” using sign language.
Gorney was stunned! Patterson tried to steer the conversation back to calmer territory, but Koko seemed amused by her own joke. Humor, it turned out, was also part of her repertoire.
The exchange suggested that Koko understood context. A joke requires timing, tone, and awareness. All of them were present. But that wasn’t enough for Koko; she pushed beyond her limits. Then, she learned how to ask for a gift.
In 1983, when asked what she wanted for her birthday, Koko signed cat. At first, she was given a stuffed toy. She looked at it, then signed sad.
Later that year, researchers brought her a real kitten — a tailless gray one she named All Ball. The name came from how the kitten looked curled up in her hands.
Their bond was immediate. Koko cradled All Ball gently, groomed him, and even signed love cat. The photos soon made the cover of National Geographic once again. But just when Koko found a furry friend, things quickly went sour.
A few months later, All Ball escaped from the enclosure and was struck by a car. Patterson dreaded telling Koko. When she finally did, Koko signed bad, sad, cry, frown.
For days, she refused food and sat motionless in her enclosure. Researchers documented her gestures of mourning — the first recorded signs of grief in a gorilla.
That tragedy altered the project’s perception. Language for Koko extends beyond getting food or toys. She was using it to process loss — an act as human as it was heartbreaking, and that brought Penny to a heartwarming conclusion.
The only real difference that seems to separate Koko from humans is that they can’t articulate their feelings through words.
For hours, Koko sat facing the wall, silent. Penny Patterson described the scene as “the most human moment I’ve ever witnessed from a gorilla.”
But Koko’s love of cats didn’t die with All Ball. She soon found new friends in several other kittens and was just as gentle and nurturing with them. And with her emotional progress, they didn’t know Koko had been a keen observer for a very long time; that she was preparing herself for the ultimate mic drop.
When National Geographic released the images of Koko holding All Ball, public fascination surged again. Letters flooded the Gorilla Foundation from around the world.
Readers described her as “a mirror for humanity.” Donations poured in. Koko had become a global figure, bridging empathy between humans and apes in a way no research paper ever could. But her fame came with scrutiny.
Linguists accused Patterson of reading too much into Koko’s signs. She rejected that criticism, insisting that Koko’s emotions were genuine — “You can see it in her eyes.” But the debate didn’t seem to stop, and Koko’s story earned some serious media attention.
In the following years, Koko’s renown attracted celebrities, scientists, and journalists. Most came expecting novelty and left disarmed by her gentleness and intelligence.
Television crews filmed her joking and requesting snacks. Schoolchildren sent her drawings. She received fan mail in multiple languages — all addressed simply to “Koko the Gorilla.”
But one visitor in 2001 stood out from the rest — a comedian who would share a connection with Koko that transcended species and words.
When Robin Williams met Koko in 2001, she was 30 years old. The comedian entered the enclosure quietly, hands open. Koko approached, then suddenly hugged him.
Within minutes, they were playing. She tried on his glasses, rifled through his pockets, and tickled him. Williams laughed uncontrollably — a sound Koko mimicked with a breathy, rhythmic huff.
Later, when shown a VHS box of one of his movies, Koko pointed to his face and signed funny. And yet, when Koko found her one true friend that wasn’t one of the researchers, she had to experience the hardships of grief once again.
13 years later, in August 2014, the Gorilla Foundation staff informed Koko that Robin Williams had died. She listened silently, then signed woman and cry after seeing a tearful caretaker.
Her demeanor changed instantly. She sat down, lowered her head, her lips trembling, and remained still for nearly ten minutes. It was the same posture she had shown after losing All Ball!
Grief, it seemed, was a language all its own, and you don’t have to be a human to feel it. But despite her deep connection to people, Koko was still, fundamentally, a gorilla. She became strongly drawn to her own kind.
By the early 1980s, Koko had begun showing maternal behavior. She cradled dolls, gently moved their hands into signing positions, and rocked them the way mothers rock infants.
When shown photos of gorilla mothers, she signed me and that. She also requested a baby of her own, though attempts to introduce males for breeding were unsuccessful.
Despite one miscarriage, she remained nurturing toward her toys and kittens. To her caretakers, the longing was clear: Koko wanted to pass on what she had learned. But there were moments when Koko wasn’t even nurturing.
Yes, she wasn’t always saintly. At age three, after breaking a toy cat, she blamed her caretaker, signing Kate, cat. The incident became one of the first recorded examples of deception in an ape.
But another event definitely caught Koko red-handed! She climbed onto the kitchen counter, but it couldn’t take the weight of a five-year-old, almost 300-pound gorilla, so the top caved in! When Patterson asked what happened, Koko signed, “Kate there bad.”
Patterson laughed at the pattern. Lying requires awareness of what another individual knows — a small but significant marker of higher intelligence. And she wasn’t the only cutie trickster in the house.
When Michael ripped a volunteer’s jacket, he immediately signed Koko. When challenged again, he signed Penny, then finally Mike.
It was a small comic moment, but a telling one. The gorillas understood blame, and they eventually learned to shift it.
For Patterson’s team, these moments of mischief were gold. But Koko and Michael’s relationship with the English language also went beyond sign language.
By the late 1980s, researchers noticed Koko and Michael responding correctly to verbal prompts even when signs weren’t used! Tests confirmed they could recognize over 1,000 spoken English words.
This defied the motor theory of speech perception, which held that language comprehension depended on the ability to vocalize sounds. They understood words they physically couldn’t pronounce.
In one session, Patterson told Koko, “One more, then you turn it off.” Koko complied immediately and turned off the faucet! Spoken language, it seemed, had become part of her silent world. And the older Koko got, the more complex questions she could follow.
During a filmed experiment, Koko was offered four future companions. When asked verbally which she preferred, she selected the card representing “two female gorillas and one male.”
Her choice matched a natural gorilla troop structure — a detail she could not have guessed by chance. That moment convinced even some skeptics.
Understanding grammar was one thing. Understanding social structure was another. Koko appeared to grasp both. Not only that, she also used the sounds of some words to come up with her own signs!
Koko’s creativity extended beyond comprehension. One day, Koko was craving some “browse.” It’s a kind of leafy green vegetable mix that she was given between her meals.
While she’d had it almost every day and heard its name many times, it had never been given a specific sign. Showing just how clever she was, she began touching her brow repeatedly.
At first, it confused her keepers, but then they realized Koko knew that “brows” and “browse” sounded similar, and by making the connection, she was able to communicate just that. Then, her words got even more detailed.
She learned to combine known words to describe new objects. Eye and hat meant “mask.” Finger and bracelet meant “ring.” Each combination showed flexible understanding of parts and wholes.
This kind of symbolic thinking — joining two ideas to represent a third — had previously been considered uniquely human.
When tested, she applied these inventions consistently across weeks. Her handlers realized she was building a dictionary of her own. But that wasn’t all; Koko and Michael had even more creative talents hidden up their huge furry sleeves.
Both Koko and Michael were introduced to painting in the late 1970s. Using brushes and non-toxic paints, they produced abstract works that researchers believed reflected emotional states.
Michael’s piece, Apple Chase, used black and white, inspired by his dog Apple with black and white fur. Koko preferred bright colors, often choosing pinks and oranges when painting about love and affection.
One might assume she’d use yellow to symbolize her love of bananas, but instead, Koko chose the colors humans also associate with warm feelings. But as her artistic experiments drew attention, Koko used her voice to communicate an important topic threatening us all.
By the 1990s, Koko’s fame was global. The Gorilla Foundation relocated to Woodside, California, where she lived with her companion, Ndume, in a sprawling enclosure built for comfort and research.
She appeared in documentaries, news specials, and educational programs. Her face became a symbol for animal intelligence — and, to some, human lies.
Then years later, in 2015, the French conservation group NOE collaborated with the Gorilla Foundation to record a message from Koko for the United Nations Climate Change Conference in Paris. And that message would soon shock audiences.
The handlers informed Koko about what was at stake with the upcoming United Nations Climate Change conference and asked for her thoughts.
After being briefed, Koko signed: I am flowers, animals. I am nature. Man Koko love. Earth Koko love. But Man stupid. Stupid!
She then proceeded to sign “fix earth,” and nature sees all of us. Critics pointed out that the video was edited for clarity, but the sentiment — whether it was guided or not — echoed the lifelong warnings of another voice from the wild.
A decade after Koko’s viral plea, her message resurfaced in a different form. In 2025, at the Forbes Sustainability Leaders Summit, the late Dr. Jane Goodall delivered her most vulnerable reminder.
In one interview, she reflected, “We humans are the most intellectual species to walk the planet, but we’re not intelligent. If you’re intelligent, you don’t destroy your only home.”
Goodall’s words framed Koko’s message in a broader truth: both women — one human, one gorilla — were urging us to protect the world we share. And as Goodall spoke, many thought back to the gentle gorilla who’d signed her final message years before.
On June 19, 2018, Koko passed away in her sleep at the age of 46. Staff members found her lying peacefully, a cat toy beside her.
The Gorilla Foundation released a statement calling her “a symbol of interspecies connection and compassion.” Tributes came from scientists, artists, and children who had grown up watching her story.
Penny Patterson, then 71, wrote: “Koko taught us that love and understanding can cross any boundary.” In the stillness of that day, the project that began with a single sign ended with something far greater — proof that communication, in any language, begins with empathy.
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