Millions are mourning a gorilla, and that’s a good sign for humanity. Koko, a western lowland gorilla, died in her sleep at age 46 this week.

Koko started learning a version of American Sign Language adapted for apes when she was a year old, and 45 years later she could comprehend 2,000 words and “speak” 1,000. As the subject of news article after news article and numerous documentaries, she had cemented her place in the zoological zeitgeist. Koko, in short, was a superstar.

Celebrities everywhere court controversy whether they intend to or not, and Koko was no exception. Sceptical scientists questioned how much of Koko’s communication actually came from her, and how much came from our own preconceptions and projections.

Researchers have argued in the past that apes do not possess the same complex language-processing abilities that humans do. They have also said that humans communicate extemporaneously about the things around us, conversing for conversation’s sake alone. Apes, on the other hand, prefer functional language. They use their words when they want something concrete.

That gap points to emotional differences between us and our simian ancestors that researchers who spend years raising apes almost as their children are eager to disprove or overcome. And in Koko’s case, there were certainly obstacles.

Sometimes, in response to a prompt, Koko would make the wrong sign, or say the word “nipple” with apparently randomness, and her caretaker would call her “silly” before trying again. Other times, the caretaker’s questions seemed designed to elicit responses that made it seem as if Koko understood more, or more deeply, than she really did.

Sure, Koko could pair an impressive number of words to objects and phenomena, but when she signed “happy” or “love”, did she really feel those things the way we do? We may all have been complicit, critics contend, in interpreting Koko’s gestures and signs in way that told us what we yearned to hear.

But, boy, did we want to believe.

When Koko watched a sad movie, her eyes watered.

When Koko’s kitten, All Ball, was killed by a car, Koko reacted, her researchers said, with unambiguous anguish — and the footage they released suggested they weren’t exaggerating. “Bad, sad, bad,” she signed, shoulders hunched. “Frown, cry, frown.”

She really did seem to be frowning, and she really did seem to be crying. The world was rapt.

When Koko met Robin Williams, she smiled and they tickled each other. Years later, when he died by suicide, she spent the afternoon sitting sombre in her enclosure. Whether Koko actually matched Williams’s name to their encounter is far from certain — she may as well have been reacting to the distress of her caretakers — but that did not deter observers, who shared en masse evidence of Koko’s grief.

Maybe most important, those who met Koko, from reporters to actors to the late Mister Rogers, almost all say they felt something.

How much apes really do resemble us in their emotional range and mental capacity will probably remain a mystery for longer than many of us will live. But when it comes to Koko, that may not really matter. Our response to a creature at once so like us and so different was to seek out the similarities — to experience empathy and to trust that Koko experienced it, too. It didn’t matter that she didn’t speak English the way we did, or even that she wasn’t human the way we were. What mattered was that somewhere in Koko’s eyes, we saw ourselves.

•Molly Roberts is an editor, writer and producer for The Washington Post’s Opinions section