Humans are exceptional beings, so we like to think. The so-called lower animals lack complex syntax for language. They simply are not as conscious. Many philosophers believe only humans understand that others have their own personal thoughts, which philosophers term as having a theory of mind, without which we would lack our empathy and deception. So goes the point of view. Theory of mind has implications that reach far into our notions about consciousness. For one, experiments suggest that the degree of consciousness has no clear correlation to matter, brain size in this case.
Biologists are wary of exclusionary assertions for human beings. We are not, apparently, the only species with a theory of mind. Biologists have found it in various mammals, ranging from gorillas to goats. Two recent studies suggest that theory of mind can extend beyond mammals to birds. Consider a recent article in the Proceedings of The Royal Society, in which Bernd Heinrich and Thomas Bugnyar, University of Vermont, Burlington, describe experiments conducted on ravens. As birds, ravens are known to be clever and sociable, and for this reason, the scientists set out to find how the ravens would respond to human gaze.
Gaze response helps measure the development of theory of mind in human children. At about 18 months most children can notice another's gaze, follow it, and infer things about the gazer from it. Autism is revealed when a child fails to develop this skill, as the autistic child also fails to understand that other people have minds.
To test whether ravens could follow gaze, Dr Heinrich and Dr Bugnyar used six six-month-old hand-reared ravens, and one four-year-old. With the room divided by a barrier, the birds were placed, one at a time, on a perch. An experimenter sat about a metre in front of the barrier. He moved his head and eyes in a particular direction and gazed for 30 seconds before looking away. Sometimes he gazed up, sometimes to the part of the room where the bird sat, and sometimes to the part of the room hidden behind the barrier. The experiment was videotaped.
Dr Heinrich and Dr Bugnyar found that all the birds were able to follow the gaze of the experimenters, even beyond the barrier. In the latter case, the curious birds either jumped down from the perch and walked around the barrier to have a look or leapt on top of it and peered over. There was never anything there, but they were determined to see for themselves.
A suggestive result, but not, perhaps, a conclusive one. But while at the University of Austria, Dr Bugnyar conducted another study. Its results were published last month in ,, and it suggests that ravens may have mastered the art of deception too.
Wanting to determine what ravens learned from one another while foraging, in his experiment Dr Bugnyar noticed strange behavior between two male birds, Hugin and Munin, the first subordinate, the second dominant.
They had to figure out which color-coded film containers held cheese, then pry off the lids and eat the morsels. The subordinate male excelled at this while the dominant was rather slow in working things out. However, Hugin could only swallow a few bits of cheese before the dominant raven, Munin, bullied him aside. Although it comes as no surprise, this indicated that ravens are able to learn about food sources from one another. They are also able to bully each other to gain access to that food.
Something surprising did happen. Hugin, the subordinate, tried a new strategy. As soon as Munin bullied him, he headed over to a set of empty containers, pried the lids off them and pretended to eat. Munin followed, whereupon Hugin returned to the loaded containers and ate his fill.
At first Dr Bugnyar could not believe what he was seeing. Hugin, he is convinced, was clearly misleading Munin.
Munin grew wise to the tactic, and would not be led astray. He learned from Hugin and tried to locate food on his own. Hugin became furious. "He got very angry," says Dr Bugnyar, "and started throwing things around."