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SHEEP use facial clues to tell friend from foe in their flock. And like
people, they use the right side of their brain to tell each other apart, a
finding which could provoke more arguments about how our brains became
asymmetrical.

Jon Peirce and his colleagues at the Babraham Institute in Cambridge knew
that external cues such as horns help sheep spot one of their kind. But they
decided to find out if they are also expert at spotting familiar faces in a
flock.

They trained sheep to pick one of two faces at the ends of a Y-shaped path.
First they had to choose between two sheep from their own flock, then between
two unfamiliar sheep. When shown the whole head, they always picked the correct
face. But when Peirce covered up the head and ears, sheep could only correctly
choose faces they knew well.

鈥淭hey can see their mates really well,鈥� he says. With experience they learn
to use subtle, internal facial cues such as the distance between their eyes,
rather than external cues such as their friends鈥� fleeces.

And he found that sheep, like people, use the right side of their brain to
recognise faces, something never seen before except in primates. This fuels the
debate on how the two halves of our brain evolved their different roles. Some
researchers claim that centres controlling language and handedness developed
first in the left hemisphere, pushing face recognition into the right.

But Peirce thinks that his sheep, which naturally enough don鈥檛 speak or
write, suggest that the face recognition centre arose first. 鈥淲e were dealing
with social interactions before tools,鈥� he says. Michael Corballis, a
psychologist at the University of Auckland, agrees: 鈥淩ight-hemispheric
specialisation seems to be more primitive in an evolutionary sense.鈥�