Before considering this question it is interesting to review briefly the evolution of the (1) ______ 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 been to (2) ______ study the way they behave when giving different kinds of puzzles. For example, an ant (3) ______ possesses a complex routine of behaviour, but can it think The answer is what if an ant is (4) ______ 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 wrong turnings. In the (5) ______ end, however, after it has to worry its way through often enough, it does learn to get to its (6) ______ nest without going into any of the blind alleys. As one moves up the evolutionary scale the test of mind-power exemplified by solving the problem of getting through a maze be (7) ______ comes very simple. Among mammals, for example, the maze is an inadequate test. The (8) ______ 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. (9) ______ The next, more subtle test of mental ability is to see what level an animal can think about (10) ______ something when it is not there.