Fish have been shown to learn, recognise and distinguish human faces for the first time. Through a series of experiments, archerfish were able to choose one learned face from 44 new faces with a high degree of accuracy, suggesting a complex brain is not required to recognise human faces.

Researchers from the University of Oxford and the University of Queensland were looking to see if complex brains are required to recognise faces. Previously, it had been thought only primates could achieve this because of the difficulty level of the task. However, there is increasing evidence to show non-primates can also discriminate between different human faces – whether this ablility is learned, or the result of having a larger, more complex brain, is unknown.

Cait Newport, first author of the study published in Scientific Reports, said distinguishing between human faces is difficult because they all share the same basic features – two eyes, a nose and a mouth. "To tell people apart we must be able to identify subtle differences in their features. If you consider the similarities in appearance between some family members, this task can be very difficult indeed," she said.

"The fact that the human brain has a specialized region used for recognizing human faces suggests that there may be something special about faces themselves. To test this idea, we wanted to determine if another animal with a smaller and simpler brain, and with no evolutionary need to recognise human faces, was still able to do so."

archerfish spit at faces
Archerfish spat at faces they recognised Cait Newport

Archerfish is a species of tropical fish that spits jets of water to knock down flying prey. In the experiment, the fish were presented with two computer images of human faces and trained to choose one, using their jets to spit at them.

Fish were then shown the learned face with up to 44 pictures of new faces. Findings showed they were quickly able to choose the learned face, getting it right 81% of the time. After removing features like head shape and colour, the fish still had an 86% accuracy rate.

This is evidence that archerfish have strong visual discrimination abilities. Newport said: "Fish have a simpler brain than humans and entirely lack the section of the brain that humans use for recognising faces. Despite this, many fish demonstrate impressive visual behaviours and therefore make the perfect subjects to test whether simple brains can complete complicated tasks.

"The fact that archerfish can learn this task suggests that complicated brains are not necessarily needed to recognise human faces. Humans may have special facial recognition brain structures so that they can process a large number of faces very quickly or under a wide range of viewing conditions."