The Mirror Test Is Broken

Alex Jordan had just surfaced from a dive off the coast of Corsica when he called me back last summer. “We’ve put mirrors in the wild,” he said. “It’s always a bit of a nightmare.” With the help of his students, he’d set them in the sinuous green seagrass of an underwater meadow, where a diverse community of fishes live and breed. Shier species, he told me, tend to avoid their own reflections, but more aggressive ones lunge toward what they take to be a rival in the mirror. At times, their headbutts crack the glass.

Jordan’s mirrors were meant specifically for wrasses, one of the largest families of marine fish. His favorite Mediterranean species, the rainbow wrasse, certainly would have reason to admire its own ribbon-candy body with green and orange stripes. But when Jordan and his students started the experiment, a small and drab species called the black-tailed wrasse exhibited the most curious behavior. These fish relaxed their fins and spun repeatedly around their central axis before the mirror. “It looks like they’re doing a backflip, which is the most bizarre thing for them to do,” he said.

Jordan, an evolutionary biologist at the Max Planck Institute of Animal Behavior, has done extensive underwater fieldwork in Central Africa’s Lake Tanganyika and the Great Barrier Reef. Still, never once in his decade-long career had he observed a wild fish moving like the black-tailed wrasses. From the first time one of his students had shown him a video of the behavior, in 2019, Jordan had suspected that the fish were checking whether the movements of the mirror image matched their own activity. Perhaps they even recognized themselves.

Jordan would need to collect data for many months before drawing any firm conclusions. If indeed the black-tailed wrasses were showing signs of self-recognition—and not just in a laboratory tank, but while swimming freely in their habitat—then the study of animal minds would be headed for an unexpected turn.

Self-awareness is supposed to be one of the rarest mental faculties in nature, and one of the hardest to detect. To become the object of one’s own attention allows firsthand experience to be transformed into inferences about others, plans for the future, and maybe even the anticipation of death. But how can we look into the mind of an animal, to determine whether it has a sense of its own existence?

In 1970, a psychologist named Gordon G. Gallup Jr. unveiled a simple test: He placed mirrors in the cages of captive chimpanzees, and watched how they reacted. At first the chimps made threatening gestures and vocalizations, as if they were seeing social peers. After a few days, some started using the mirrors to examine parts of their bodies they could not normally see, like their anuses and teeth.