RECOGNISING, remembering and thinking about others and their emotional states, as well as being able to put yourself mentally in their place, are key features of primate minds. But what about other mammals: do they possess any of these social cognition skills?
It appears they do. And we have found many of them in a most unlikely species: sheep. Our studies show that sheep are remarkably good at recognising, differentiating and remembering both sheep and human faces 鈥� an ability that suggests a level of mental and social sophistication way beyond what they are usually credited with.
We have found that sheep can recognise the faces of at least 50 other sheep and 10 humans 鈥� although this is probably a considerable underestimate 鈥� and that after seeing them in tests over the course of a few weeks they can remember all these faces for at least two years. Much like humans, they tend to analyse a face first by simple external features such as outline and the appearance of the ears and hair. When a face is very familiar they look at internal features such as eyes, nose and mouth 鈥� this we discovered by showing them different facial stimuli that we had selectively edited on a computer. Also like humans, they have trouble recognising faces that are upside down.
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How do their recognition skills compare with ours? We tested this using a computer morphing program that gradually merged two different sheep or human faces to the point where they looked identical. We found that sheep, like humans, could still discriminate accurately between the two images when only a 5 per cent difference remained between them. This is pretty impressive considering how much more acute our visual ability is compared with theirs.
Sheep share another of our basic recognition skills: they can pick up on emotional cues in facial expressions. We have shown that they can distinguish between different expressions in humans, and that they can detect changes in the faces of anxious sheep. They also prefer smiling human faces to angry ones. Even more astonishing is that sheep find some sheep faces more socially or sexually attractive than others. Female sheep tend to be more attracted to the faces of older males: when they see one that grabs them, it activates the parts of the brain that control pleasure, particularly through the release of the neurotransmitter dopamine. What makes a particular face more attractive than another may be partly due to their mother鈥檚 influence, since sheep that have been raised with a goat mother find goat faces more stimulating.
So much for attraction, but what about deeper emotions? Can a sheep emotionally 鈥渂ond鈥� with a human, and do sheep feel for their shepherds what dogs feel for their owners? Normally, the neural circuits in the parts of a sheep鈥檚 brain that control face recognition categorise humans in the same way as they do dogs, and distinctly from other sheep 鈥� presumably because we represent a potential threat. However, this demarcation can change through experience. The faces of humans who look after sheep can end up being categorised in the same way as a highly familiar member of the flock. Friendly humans effectively become honorary sheep.
This implies that sheep feel an affiliation with their shepherds. But whether this equates to a human-like emotional state 鈥� and whether sheep experience deeper feelings such as love 鈥� depends partly on another question: to what degree are sheep conscious? Sheep use the same specialised regions in the temporal and frontal cortices of the brain as humans do for face recognition. These are principally located in the right brain hemisphere which means that, like us, sheep focus on the left side of a face. These areas are also important for higher cognitive functions such as consciousness and self-awareness. So how mentally sophisticated are they?
One way to investigate this is to test their powers of imagination 鈥� to what extent they use mental imagery. The ability to form and use imagery is a key component of a conscious brain. Human brains register the same patterns of activity in the face-processing areas whether seeing particular faces or imagining them. This happens with sheep brains too, when the animals are led to believe that a familiar individual is present even though they cannot see them. For example, it occurs when a ewe can hear or smell, but not see, her missing lamb and when sheep are played videos in which a familiar individual is shown in their home pen and then suddenly disappears from view. Sheep can also recognise other sheep from photographs taken from different viewpoints, even when they have been trained to recognise them from only one. They may do this by mentally rotating the picture back to the familiar view, possibly using specialised cells in the frontal and temporal cortices that can respond to faces equally well from different angles.
All this suggests they have at least the potential for consciousness, in that they can use mental imagery to 鈥渢hink鈥� about absent individuals. However, it appears that they cannot sustain their imaginative powers for long. If required to recall an image more than 10 seconds or so after seeing it, they fail. And being able to form a conscious mental image of another individual whom you know is nearby is not the same as being able to do this of your own volition, without any external cues to prompt you. For this, you need to be conscious of yourself and the workings of your mind.
We have no evidence that sheep have such a sense of self-awareness. The classic test for self-awareness is being able to recognise yourself in a mirror. Most animals simply do not seem able to do this, even after a lot of time spent standing in front of one, and sheep are no exception. Indeed, showing socially isolated sheep their image in a mirror is a great way to make them feel less isolated and reduce their stress!
Since consciousness and self-awareness are necessary for generating thoughts about the past and planning the future, sheep 鈥� and animals in general 鈥� are not strong on mental time-travelling. The only time a sheep might generate images of an individual from the past is when it encounters strong environmental cues, such as going back into a field where it was chased by a dog or seeing a particular food that it had learned from its mother was good to eat. And the only future a sheep is likely to contemplate is the immediate one predictable on the basis of the present.
Clearly, sheep are some way down the cognitive ladder, despite their impressive social cognition skills. But they are not as dim-witted as their public image suggests. And if sheep can do all this, it is likely that many other mammals can too.
