68 THE LAMARCKIAN DOCTRINE 



resistant. But it can be shown that the resisting power which the 

 individual develops is radically different in kind from that which 

 the race evolves. 1 The latter power, therefore, cannot have arisen 

 through the inheritance of acquirements. In any case, the fact 

 remains that many diseases and other conditions (e.g. tuberculosis, 

 slum-life, and alcoholism), which confer increased resisting power 

 on the race, not only confer none on the individual, but actually 

 tend to destroy any that he may possess. 2 Here the race evolves 

 in a direction precisely contrary to the direction taken by the 

 acquirements of the individual. 



107. Another point of contrast, important but seldom noted, 

 between the two hypotheses, is the differing complexity of the 

 racial change which would necessarily result on the one hand 

 from natural selection, and on the other from the transmission of 

 acquirements. 



108. The natural inference from the theory of Selection, the 

 theory which attributes the evolution of a character, not to the 

 amount of use to which it is subjected but to its utility (selection 

 value), is that progressive evolution proceeds on lines of comparative 

 simplicity. We have abundant evidence that structures that do 

 not assist appreciably in the preservation of life or in the struggle 

 for offspring, for example the wings of a species of bird to which 

 flight has become useless, or the special features of our prize breeds 

 of plants and animals, tend to deteriorate when no longer selected. 

 It is a reasonable inference, therefore, that a certain stringency of 

 selection is necessary for progression, that a lower degree of 

 stringency suffices for the maintenance of a structure, and that a 

 still lower degree of stringency, or, even more, complete cessation 

 of selection, is followed by retrogression. These inferences are 

 borne out by what we observe in nature. For instance, as we 

 shall see later, the human race is undergoing progression in a few , 

 particulars. 3 The mass of human characters, however, are 

 stationary or nearly so. They were evolved during different but 

 overlapping periods of a long-extended past, and their progression 

 ceased when further increase was not of utility. No matter how 

 much used or useful, they are merely maintained at a certain 

 standard of efficiency. Thus apparently the human hand, heart, 

 lungs, liver, and many other characters have changed little, if atj 

 all, during thousands of years. Lastly, many human structures,! 

 having quite lost utility, have become vestigial, presumably through j 

 cessation of selection. The germ-plasm has so altered that they! 



i See 432. 2 See 435. 3 See chapter xiii. 



