30 SENESCENCE AND REJUVENESCENCE 



in general. The facts show clearly enough that different degrees 

 of intelligence exist in different organisms, and we cannot deny 

 that even the simple organisms show something remotely akin 

 to intelligence. On the other hand, many of the supposed funda- 

 mental differences between the organism and the inorganic world 

 have disappeared in the light of scientific investigation. But 

 even supposing that we shall some day demonstrate the essential 

 unity of the universe from the simplest inorganic system to the 

 highest organism, when that is done there is no reason to believe 

 that the real problem of teleology will be eliminated ; it will doubt- 

 less still be before us as a problem concerned, not with any single 

 group of organisms, nor with all organisms, but with the world as a 

 whole. In other words, on the basis of such a conception there is 

 not merely an analogy but a fundamental similarity between the 

 river with its current and channel, the organism constructing itself 

 by its own functional activity, and the man constructing and 

 running a machine. And this remains true whatever the final 

 solution of the teleological problem. 



But as the complex structure of the human organism and also 

 the machine which it has constructed have constituted essential 

 factors in the development of human intelligence, so also in other 

 organisms the approach to anything like intelligence in the broadest 

 sense is manifestly associated with the development of structure. 

 The more complex the structure, particularly of the nervous sys- 

 tem, the closer the approach to intelligence. This is again merely 

 a special case under the general relation between structure and 

 function: the more complex the structure the greater the possi- 

 bilities of function. Moreover, even in man a very complex 

 structure is developed before we can find any evidence of intelli- 

 gence. In short, all the evidence along this line indicates that 

 anything which we are able to recognize as intelligence is not a 

 primary function of the organism, but one which becomes apparent 

 only in a highly complex structure. Just as clearly does the evi- 

 dence indicate that there is no real break in the series between the 

 simplest morphogenetic activity of the organism and the man 

 building and controlling the machine. But because the man builds 

 and runs the machine with a definite purpose in mind, it does not 



