New research suggests that fish can recognize human faces, putting to bed a previous theory that only animals with large brains, like primates, can accomplish such a complex task.
The research, published in the journal Scientific Reports, was led by Canadian scientist Dr. Cait Newport, who is a Marie Curie Research Fellow in the Department of Zoology at the University of Oxford in England.
Humans have an entire part of the brain dedicated to recognizing faces, called the neocortex. Newport wanted to find out whether animals without a neocortex can also recognize faces.
This is something that humans do all the time, but it's more complex than it seems; we all have two eyes, one nose and a mouth.
"You have to be paying attention to subtle differences in the features or the spatial relationship of them, and it's quite a difficult task," said Newport, who spoke to CBC's Bob McDonald on Quirks & Quarks.
The fish she studied were able to spot the same face with 86 per cent accuracy. She said that, contrary to previous thinking, this suggests that animals don't need special brain structures to distinguish faces.
"What we think is, instead, that maybe humans have actually just applied a visual system that was already capable of complex pattern recognition," she said.
The fact that the fish can also recognize complex patterns suggests they also have this visual system, even without the extra brain power that humans have.
"So it's probably evolved early on, this ability," Newport said.
Study used 'really cool' spitting archerfish
She studied archerfish, a species of tropical fish from Australia. These fish are "really cool little guys," said Newport.
"They swim at the top of the water column. And when they see an insect above in overhanging branches or flying above, they're able to spit a jet of water out of their mouth and knock it down and swim to where the insect landed to eat it," she said.
And the fish, unlike dogs, horses or pigeons that have undergone similar studies, are not domesticated or accustomed to humans.
Newport and her team trained the fish, which "naturally want to spit at everything in the room around them," to spit at computer monitors placed over their tanks.
"Every time they spit at something on the computer monitor, we would give them a piece of food," explained Newport.
The team started by moving a cursor around on the screen, then moved on to shapes and eventually to faces. The faces were selected from a database created by the Max Planck Institute.
The video below, from the University of Oxford, shows the fish completing the task.
Newport said they chose faces that were relatively similar — they were all of German women who had similar bone structure and skin colour.
Newport put two images of faces up on the monitor for the fish to spit at — but only spitting at one of the faces would get the fish their food.
"When the fish first started, they totally were just choosing at random. So they were getting it about 50 per cent correct," she said. "And then, as they got used to it and they were trained and they realized food was associated with only one face, then they would start only choosing the one face."
The big test was to see whether the fish could remember even very similar faces. Newport started introducing new faces to see if they were still able to select the one they had learned would get them food.
But this time, the faces all had similar shapes, and they were all in black and white, making it even more difficult for the archerfish.
And still, the fish prevailed.
"They were very accurate," said Newport, with the fish able to choose the correct face about 86 per cent of the time.