One such researcher, Dr Richard Byrne from the psychology department at the University of St Andrews, goes even further by suggesting that one of our most distant cousins in the ape world holds some of the most vital clues to understanding how humans became so intelligent. The animal he is referring to is the orangutan of Borneo, which derives its name from the Malay for ``forest man''. Dr Byrne believes that the closest we can get to finding out how our hominid ancestors behaved is by understanding how the orang-utan thinks and reacts to the world around it.
Dr Byrne's thesis is that human cognition - thinking and language - did not just appear but evolved over a vast tract of time as adaptations to survival. Many scientists have believed it would be impossible to trace this evolutionary sequence because bones and tools provide relatively limited insights. Dr Byrne and others, however, believe that the past 15 years of research on living primates have changed the picture dramatically. Like humans, the apes can manipulate and deceive their companions and have a remarkable understanding of cause and effect and the beliefs and intentions of others in the social world.
Most attempts to discover what our ancestors were like usually begin with fossils. Dr Byrne argues that this involves an awful lot of idle speculation. For instance, when the remains of a Neanderthal were found in a shallow grave sprinkled with petals, archaeologists talked about a ``burial'' and the rudiments of culture. The flowers could just as easily have fallen in by chance, says Dr Byrne.
Studying living primates at least augments this kind of speculation, though it too has its limitations. Any discussion of intelligence suffers from the difficulty of defining what this means in animals. Human intelligence evidently evolved from something more primitive and so we assume that our ancestors must have had some kind of intellectual capacity. Intelligence, however, is a nebulous concept. Psychologists have been unable to design an IQ test for humans free of cultural, linguistic and educational bias, let alone work out how to determine intelligence in a range of species.
Some species have had a bad press in the intelligence stakes. Take sheep, for instance. Dr Byrne describes the time he spent with Gujarati shepherds on the Little Rann of Kutch in India. "It seemed a familiar scene of sheep being pushed around," he says, "because they are not overly bright." He then noticed the sheepdogs asleep under a tree. The sheep had learnt what the shepherds' whistles meant and were rounding themselves up. As Dr Byrne says: "Sheep are not primates like us, and so we easily underestimate their capacities."
It is difficult to tell whether any particular behaviour is truly intelligent. Many animals demonstrate behaviour that looks remarkably clever, but they are, in effect, genetically programmed to be good at a particular task. Birds, for instance, are adapt at imitation. European marsh warblers mimic the songs of between 78 and 212 other species of bird. Dr Byrne says that this is mere ``tape-recording'' and the birds have no understanding of what they are copying. True imitation shows a high degree of intelligence because it requires two quite difficult operations. One is to see the world from another's perspective and the other is to put together a complex sequence of behaviour in the correct order. Orang-utans, when brought up in the presence of humans, copy a range of activities, from washing clothes to weeding the garden. Dr Anne Russon, who is a primate researcher at the Orang-utan Rehab-ilitation Centre in Borneo, cites the time she came across a female called Supinah trying to start a fire. Dr Russon assum-ed that the orang-utan had hold of a can of water, but when the ape became wreathed in smoke she realised that Supinah had in fact stolen a can of paraffin to start the fire.
It appears that primates are capable of imitation, but on closer inspection only the great apes - gorillas, chimpanzees, pygmy chimps and orang-utans - master all the concepts required. To be able to see things from someone else's perspective requires a knowledge of what they might see, as well as understanding your own self. When non-ape monkeys are presented with mirrors, they react to their own images with threatening behaviour, no matter how long the mirror is left in their cage. Gorillas, orangutans and chimpanzees, however, treat the image as a copy of themselves and will often use the mirror to examine parts that they normally cannot see, just as human beings do.
There are two main theories as to why the great apes have been able to evolve a level of intelligence super-ior to that of other animals. One idea has to do with the way apes gather their food. Dr Byrne believes that this could be the key factor in how apes, and ultimately humans, evolved intelligence. Take gorillas, with their big banana-like fingers. They are rotund vegetarians and process each kind of plant they eat in highly complex ways, requiring a good deal of mental processing. Adult gorillas dexterously juggle nettles to escape being stung, but youngsters who have not quite got to grips with the concept gingerly touch the stem and nibble only the tender tips of the leaves.
Similarly, orang-utans have mental ``maps'' to navigate round the forest in both space and time in order to reach a particular tree just as the fruits are ripening. Chimps hunt co-operatively, taking up positions of scout and beater like human tribal huntsmen. They signal food availability to one another: a male will drum on trees to indicate whether they should stay or go, and in which direction the troop should head. This suggests that they can think, or plan ahead in a limited way. They are also the only species that uses a wide range of tools, from stone hammers and anvils to crack nuts, to leaf napkins for tidying themselves up after a messy meal.
The other theory about the evolution of primate intelligence has to do with the way animals in complex social groups interact with one another. This social intelligence has to cope with the occasional deception of one animal by another, which some scientists call the ``Machiavellian hypothesis''. Some even articulate their deceptions. Koko, an adult gorilla who has been taught the rudiments of American sign language, often blames the researchers who work with her for things she has done. When she sat on the sink and broke it, she signed, "Kate [her keeper] there bad." She also threatens people who annoy her with her toy crocodile, evidently displaying the childlike trait of pretending that something is real, which is an aspect of deception.
Work by Professor Robin Dunbar from the psychology department at Liverpool University strengthens this ``social'' argument for the evolution of intelligence. The neocortex, the ``thinking'' part of the brain, is larger in primates that live in large groups and have to keep track of and interact with many individuals. Furthermore, he says that the larger the neocortex is in relation to the brain, the more complex the social life of that species.
Dr Rob Barton, from the anthropology department at Durham University, also believes social interaction has been the driving force in the evolution of primate intelligence. "It seems fairly obvious that social interaction requires the integration of lots of different information at once - being able to recognise different facial expressions and react accordingly, for example - and that requires massive parallel processing. Getting food is a series of sequential tasks which are easy."
Dr Byrne is nevertheless sticking to his guns. "I'd put the question the other way round; [non-ape] monkeys live in highly complex social groups, more complex than the groups gorillas live in, or even chimps. It just doesn't make sense to say that the groups apes live in are more challenging." So why have apes shot ahead of monkeys in the intelligence stakes? "What is revealing are the things that apes do and monkeys do not," he says.
And although the groups chimps live in might be numerically smaller than those of some species of monkey, they have the richest social lives of any primate bar us and the pygmy chimps. Chimps and pygmy chimps began to evolve six million years ago, gorillas split off from the great ape lineage earlier, and orangutans even earlier than gorillas. Traditionally, because of our relative proximity in geological time, we look at chimps when we're searching for clues to how our ancestors behaved. Yet there is nothing chimps can do that orang-utans can't. Until we can pinpoint differences between the great apes' mental abilities, Dr Byrne believes that we should go much further back in time to find the wellspring of human intelligence. The "forest man" swinging in the trees of Borneo today could be the greatest living key to our own mysterious past. !