THE PARALLEL GROWTH OF OPPOSITES 31 



sense, the identification is legitimate. In the first place, 

 it is clear that, if the end of increased complexity is not 

 immunity from destruction, and if that and improvement 

 are identical, then neither can immunity from destruction 

 be the end of improvement. What, then, do we mean when 

 we speak of improvement ? Its bare definition is a change 

 which gives us satisfaction. In common parlance, the word 

 is employed in two distinct senses, and the failure to dis 

 criminate between them has been a source of error in bio 

 logical speculation. The object in the first kind of improve 

 ment is the elimination of defects ; the instrument is not 

 discarded, but retained in a less faulty shape. The process 

 in this case is usually one of simplification. In the second 

 kind of improvement, the object is increased power, without 

 reference to any other quality, and the original instrument 

 is not improved, but superseded, probably in favour of one 

 of an entirely different type. The process here is almost 

 always in the direction of increased complexity. There 

 may be some difficulty in illustrating these principles by 

 concrete examples, but the distinction of aim is real, and 

 important, and quite intelligible. 



The improvement, then, in the machine itself, consists in 

 the elimination of faults, in increased strength, in economy 

 in wear, in changes in weight or structure, which, without 

 altering its essential character, make it cost less, last longer, 

 and more surely realize the special ends for which it is de 

 signed. The evolution of the brewer s dray and the barouche 

 from the primitive cart running on wooden wheels may be 

 taken as an example of this kind of improvement. The 

 steam carriage is an example of the second kind. Instead 

 of being an improved form of the carriages which it super 

 sedes, it constitutes, by the incorporation of the motive power 

 into itself, an entirely new type of machine ; and though, 

 in respect to the main end of speedy transport, its advan 

 tages are unquestionable, it restores some of the faults 

 which had been eliminated from the older form of carriage, 

 and introduces many new ones of its own. It is heavier, 

 more costly, less durable, and far more liable both to internal 



