Before considering this question it is interesting to review briefly the evolution of (1) ______ the mind as the instrument. The commonest way that has been used to find out the relative intellectual level of creatures at different stage of evolutionary complexity has (2) ______ been to study the way they behave when giving different kinds of puzzles. For example, (3) ______ an ant possesses a complex routine of behaviour, but can it think The answer is what (4) ______ if an ant is forced to go through a maze of passages, many of which are dead ends, on its way to its nestle, it starts by making a lot of mistakes and taking a great many (5) ______ wrong turnings. In the end, however, after it has to worry its way through often (6) ______ 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 mind-power exemplified by solving (7) ______ the problem of getting through a maze becomes very simple. Among mammals, (8) ______ 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 hit university undergraduates and have, in fact, repeatedly done so. The next, more subtle test of (9) ______ mental ability is to see what level an animal can think about something when (10) ______ it is not there.