Psychologist Gordon Gallup Jr. came up with a way, over a century later. In 1970, he got four captive chimps accustomed to a mirror, and anesthetized them. While they were out, he dabbed red dye on their eyebrows. When they came to and caught sight of their reflections, they did exactly what humans would do—they stared at their faces and touched their own eyebrows. Monkeys, by contrast, made no moves to examine their own red-marked faces. They couldn’t recognize themselves in the mirror, Gallup concluded. But chimps could. [...]
Gallup wasn’t convinced. He argued that even when monkeys fail the mark tests, they can use mirrors to locate hidden objects. They understand reflections, even if they can’t recognize themselves. So given that they had an implant stuck to their heads, they may just have been trying to examine the strange heavy thing that they could feel but not see. As ever, interpreting the mirror test isn’t easy. [...]
Among these failures from the intelligentsia of the animal kingdom, perhaps none have been more surprising than humans. Many psychologists had assumed that the vast majority of children pass the mirror test between 18 and 24 months of age. But as with most such studies, people had only worked in Western countries. When Tanya Broesch from Simon Fraser University went further afield, she found that only 2 out of 82 Kenyan children passed the mirror test. Mirrors aren’t as omnipresent a feature in Kenyan homes as they are in American ones, but they still exist, and they’re used regularly. And yet, most of the children—even some as old as 6—just stared “at their image in the mirror, without any attempt at either touching or removing the mark on their forehead.” [...]
The binary nature of the mirror test—you pass or fail—is also a problem, because it “presupposes self-recognition exists in entirety or not at all,” wrote Debbie Kelly. It’s possible for a species to sort-of-pass. Take Clark’s nutcrackers—a kind of small, black-and-white corvid. In the wild, these birds bury nuts, but they’ll restrain themselves if they know they’re watched by another nutcracker. That’s what happened last year, when Kelly placed them in front of a clear mirror: they treated the reflection as an onlooker and potential thief, and refrained from burying.
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