Those of us who are not shepherds find it difficult to believe that they know the individual faces of all the sheep in his flock. We are told this so often that we must believe it. What about the ability of sheep to recognise individual humans? When I had a dog many years ago I carried out the experiment two or three times of hiding myself in a crowd of people. My dog was immediately able to recognise my face.
The dividing line between us and other animals, particularly the higher mammals — those wih a well-developed visual cortex — has been proved by experiment many times. But what about fish? Surely it’s madness to conceive of the possibility of their being able to recognise individual human faces.
Learn to be surprised ! A team of researchers at Oxford and at the University of Queensland (Australia) have shown that at least one species, the Archerfish, has been shown to be able to select a human face from 44 others. This fish normally feeds by squirting a jet of water at leaf insects above the water. By squirting or not squirting when shown photos of faces they demonstrated recognition in an irrefutable way. In one series of experiments, the Archerfish were correct 81% of the time, and in a second one, 86%.
So what can we say to all this? Once again, the usual reminder that the dividing line between us, the most intelligent species on the planet — so far! — and other species is not so hard and fast as we normally assume it to be. Perhaps those of us who have a goldfish bowl at home might want to become better acquainted with its inhabitant.