A little blue-and-black fish swims up to a mirror. It maneuvers its body vertically to reflect its belly, along with a brown mark that researchers have placed on its throat. The fish then pivots and dives to strike its throat against the sandy bottom of its tank with a glancing blow. Then it returns to the mirror. Depending on which scientists you ask, this moment represents either a revolution or a red herring.
Alex Jordan, an evolutionary biologist at the Max Planck Institute for Ornithology in Germany, thinks that this fish—a cleaner wrasse—has just passed a classic test of self-recognition. Scientists have long thought that being able to recognize oneself in a mirror reveals some sort of self-awareness, and perhaps an awareness of others’ perspectives, too. For almost 50 years, they have been using mirrors to test animals for that capacity. After letting an animal get familiar with a mirror, they put a mark someplace on the animal’s body that it can see only in its reflection. If the animal looks in the mirror and then touches or examines the mark on its body, it passes the test.
Humans don’t usually reach this milestone until we’re toddlers. Very few other species ever pass the test; those that do are mostly or entirely big-brained mammals such as chimpanzees. And yet as reported in a study that appeared on biorxiv.org earlier this year and is due for imminent publication in PLOS Biology, Jordan and his co-authors observed this seemingly self-aware behavior in a tiny fish.
Jordan’s findings have consequently inspired strong feelings in the field. “There are researchers who, it seems, do not want fish to be included in this secret club,” he said. “Because then that means that the [primates] are not so special anymore.”
If a fish passes the mirror test, Jordan said, “either you have to accept that the fish is self-aware, or you have to accept that maybe this test is not testing for that.” The correct explanation may be a little of both. Some animals’ mental skills may be more impressive than we imagined, while the mirror test may say less than we thought. Moving forward in our understanding of animal minds might mean shattering old ideas about the mirror test and designing new experiments that take into account each species’ unique perspective on the world.
The evolutionary psychologist Gordon Gallup thought up his field-defining experiment while shaving in a mirror one day as a graduate student. When Gallup took a position at Tulane University a little later, he had access to animals at the Delta Regional Primate Research Center that he could test his idea on.
Gallup started by showing a mirror to four chimpanzees, each alone in a cage. At first, the chimps reacted as if they were seeing a stranger. But after a few days, they stopped threatening and vocalizing at the reflections. They started using the mirrors to look at themselves: They cleaned food from their teeth, picked their nose, and examined their genitals. To prove that the chimps understood what they were seeing, researchers anesthetized the animals and dabbed red dye onto their eyebrows and ears. Then they returned the chimps to the mirrors. Looking at their reflections, the animals touched their fingers to the paint on their faces.
What surprised Gallup more than the chimpanzees’ success at recognizing themselves was the failure of macaques he tested at the same time. When the paper came out in Science in 1970, “it was bigger than I thought it would be,” Gallup said. “People were quite taken with the finding.”
We were speaking in his cramped office on the campus of the State University of New York at Albany, where Gallup has worked since 1975. Every surface and drawer overflowed with stacks of paper. A phone teetered atop a paper heap that covered the entire desk. Here and there, obsolete technologies peeked through the clutter: a dusty vintage computer scattered with floppy disks, VHS tapes on a rolling TV cart, a slide projector. Gallup sat on a rolling desk chair that had worn a circular hole through the carpet to the industrial floor below.