Before considering this question it is interesting to review briefly the evolution of the mind as an instrument. The commonest way that has been used to find out the relative intellectual levels of creatures at different stages of evolutionary complexity has been to study the way they behave when set different kinds of puzzles. For example, an ant possesses a complex routine of behaviour, but can it think?

The answer is that if an ant is forced to go through a maze of passages, many of which are dead ends, on its way to its nest, it starts by making a lot of mistakes and taking a great many wrong turns. In the end, however, after it has had to worry its way through often enough, it does learn to get to its nest without going into any of the blind alleys.

As one moves up the evolutionary scale the test of brain power exemplified by solving the problem of getting through a maze becomes too simple. Among mammals, for example, the maze is an inadequate test. The learning problem does not tax enough attributes of the mind. In this sort of learning, as a matter of fact, rats can beat university under-graduates and have, in fact, repeatedly done so.

The next, more subtle test of mental ability is to see at what level an animal can think about something when it is not there. The usual test is to train the animal to go through one of several doors when a light is turned on at that particular door. When the preliminary lesson has been learnt that is, that food can be obtained by going through the door with the light the more subtle trial is imposed.

The light is shone as before at one or other of the different doors and is then extinguished. After an interval the animal is released. When posed with this test rats and dogs can remember which was the lighted door only if they are allowed to keep their heads steadily pointing at where the light was.

On the other hand a raccoon, possessing a more highly evolved brain, can pace up and down until it is released and then go straight to the correct door. But it can only remember for about twenty five seconds which is the right door for any particular test.

Monkeys and chimpanzees, although they are weaker and less fierce than many other animals, possess brains which are as far along the evolutionary road as any creature other than man. Birds can perform marvels of aerobatics, they can catch insects on the wing with unparalleled skill, they can navigate in a remarkable manner half round the world and back but they cannot think and reason. In technical terms it can be said that they are lacking in insight. The abilities which they do possess are built in instincts derived from their genetical inheritance.

Monkeys, on the other hand, can reason. They can easily remember a lighted door indicating the presence of food. They can remember what kind of food they are looking for. A monkey set the problem of reaching a banana, say, hung high up in its cage can work out a system for getting it even if it involves piling boxes to stand on and then knocking down the banana with a stick.

A charming story is told about the psychologist Wolfgang Kohler, who had provided various boxes and other gear by which he proposed test a chimpanzee’s ability to think out a method of reaching a fruit hung nine feet in the air. The animal looked about it and sized up the problem. Then it took Kohler by the hand, led him to a position immediately under the banana, jumped up on to his shoulder and reached it down from there.

But evolution, although it has brought monkeys to a remarkable degree of cleverness, has stopped short at a crucial ability, the possession of which places man at a clearly superior level. Their minds cannot cope with abstract ideas. For example, an ape can be taught to fill a can with water from a barrel and take the can of water to extinguish a fire so that it can reach into a box and get food. But if the whole set is arranged on a raft the animal will continue to draw its water only from the barrel. It cannot grasp that any water, taken more conveniently, say, from the pond on which the raft is floating, will put out the fire just as well. The abstract idea that water quenches fire is beyond it.