When we talked about it in class, the examples of animal intelligence that came up were understanding of language and the abilities of guide dogs for the blind. Let's see if we can use those and other examples to get a clearer idea of what intelligence involves.
For one thing, learning by association must play a large part. The animal that understands a variety of human utterances must have associated each one with some particular kind of situation and remembered the link. Guide dogs must also build up a large number of associations, not all connected with language - they have to learn about traffic lights and crossing signs, for instance. Not only must associations be learned, they must be used in the appropriate situations. One of our cats, Roo, is certainly more intelligent than her sister Kanga. While they are waiting for their breakfast in the morning, Kanga always jumps up and rushes to me whenever I go to the place in the kitchen where their food bowls are kept. Roo generally just waits: she knows that when I am about to serve their meal I clang the bowls together as a sign. Roo has learned this and acts on it by waiting for the noise instead of running about unnecessarily.
As well as learning by association, there must be something which could be called reasoning by analogy. A trivial example of this would be using a shopping receipt as a bookmark. Receipts and bookmarks are not the same, but they may have roughly the same size, and they are both flat and thin. Using the receipt solves the problem of marking a page in a book when a bookmark is not available. The budgie who sits on people's shoulders and grooms their hair with its beak provides another straightforward example. Budgerigars are very social birds, and spend a lot of time grooming each other's feathers. Humans have nothing precisely like feathers, but hair has some features in common. So the budgie grooms the hair, the human is pleased, and the budgie has its feathers stroked. The reasoning by analogy has the correct result.
When dogs are adopted into a human family they treat their new companions as they would treat other high ranking dogs. This may also be the result of reasoning by analogy. In a similar way cats treat their humans as they did their mothers, and budgies relate to people as they do to other budgies.
The computer scientist David Gelernter wrote an interesting book called The Muse in the Machine (The Free Press, 1994) about various forms of human thought. I have adapted one of his illustrations below.
Imagine a man on a train journey. He has a briefcase with a combination lock, and would like to take something out of it to read. The combination is his birth year, 1946, he thinks, but when he tries it, the case doesn't open. What other combination could he have installed? He is sure there is some birthday connection. Maybe it's his wife's birth year, 1949? But that doesn't work either. Then he recalls thinking that faced with a four digit combination, any thief would first guess it was a year, and most likely a year beginning 19. That would leave only two digits to guess. Perhaps he had just reversed the digits? But neither 6491 nor 9491 will work. Perhaps he had decided not to use a year in any form. A date, perhaps? A day and a month could provide four digits. Maybe his birthday, the fourteenth of March? That could be expressed as 1403 - and those digits work! The case is open at last.
That kind of thing Gelernter calls "high level" thought. There is a problem to be solved, so memories related to that problem are brought into consciousness and analysed. Any stray thoughts are ignored. The memories suggest possible solutions, so they are tried until the right one turns up. Or maybe the right one doesn't turn up, and the thinking ends in frustration.
There are also lower levels of thought. Suppose the man isn't so bothered about opening the briefcase immediately - no doubt the correct combination will come to mind eventually. Why had he bought a case with such a lock in the first place? He never carries anything valuable in it, and in any case a thief could easily cut through the soft material without bothering with the lock at all. He had bought it in a little stationery shop, he recalls. He hadn't really wanted to buy anything in particular at the shop, but he was waiting for his wife and pottering about there was one way of passing the time. The briefcase had looked quite nice, and he had been amused at the combination lock idea. He had spent quite a long time looking round, and he seemed to be the only customer that afternoon. He had felt a bit guilty about leaving again empty-handed, so he had bought the case. Why had he been waiting near there for his wife? Ah, of course, they were going to a dinner party in the neighbourhood. He still had the briefcase in a paper carrier bag when they arrived for the party, and he remembers thinking that if he wasn't careful he would forget to pick it up again to take home with him. The dinner party had been very pleasant, and he remembers how nice his wife had looked in a new green dress.
At that level of thinking, there is some connection between one thought and the next, but there is no goal for the whole progression. The thoughts drift far away from the starting point.
Newton's problem was to explain why the moon didn't just fall to the earth, if it was subject to the force of gravity like an apple falling from a tree. Perhaps Newton recalled that if you throw a stone or a ball, it doesn't fall directly to the ground, but moves a certain distance sideways as well. The moon is analogous, since it too is certainly moving sideways. Maybe thinking of the moon and the earth led Newton to bring the curvature of the world into his thoughts. If you throw a ball hard enough, perhaps its fall would match the earth curving away beneath it - the ball could fall, but without ever getting any closer to the ground. That is what the moon is doing!
Einstein's problem was to explain the strange experimental fact that the speed of light always seemed to remain the same, even if the source of the light you were measuring was moving away from you or towards you. Maybe Einstein recalled a memory of his childhood musing about the classroom clock. If you raced away from the clock at the speed of light itself, you would never see any changes in the clock face, and it would seem always to tell the same time. The details of that thought experiment were not helpful, but they may have helped Einstein to seriously consider the idea that the clock time measured by an observer might be related to the speed at which the observer was moving. That was a key to the theory of relativity - other thinkers had had similar thoughts about time, but they had dismissed them as ridiculous.