ADAPTIVE GROWTH-FORCE 61 



was liable to be changed into the other. The evidence in favour 

 of the existence of an adaptive growth-force, then, is very equivocal. 

 On the other hand, if it be true, as massive evidence demonstrates, 

 that organs and structures undergo progressive evolution (i.e. 

 become larger and more complex) only when they are endowed 

 with a considerable degree of utility (i.e. selection value), and 

 retrogression only when they lack utility, the bathmic doctrine is 

 certainly untrue, and we are able to explain changes in structure 

 or function, or increase or decrease in them without mysticism. 

 Normal growth, after all, is only a form of adaptation ; it occurs 

 only when it fits the species more closely to the environment ; and 

 it is adaptation, not increase in size or complexity, that is the 

 main problem. We do not explain why a force is adaptive or 

 render it less mysterious by terming it an adaptive growth-force. 

 Moreover, the fact that breeders are able to modify plant and 

 animal types in innumerable directions is evidence of some value 

 that variations occur, not in one or two or a few directions, but all 

 round the specific mean like bullet-marks round a bull's-eye. We 

 shall see how strongly this latter hypothesis is confirmed by the 

 facts of human evolution against disease. 



93. Rejecting miracle then, there remain only two scientific 

 hypotheses which are intelligible, at any rate at first sight the 

 Lamarckian doctrine of adaptation through the transmitted effects 

 of use, disuse, and injury, and the Darwinian doctrine of natural 

 selection. Doubtless, in a way, the Lamarckian doctrine, curiously 

 combined with a belief in special creations, has been a part of 

 popular superstition since prehistoric times. Even now " the man 

 in the street " is firmly convinced that parental ' acquirements ' are 

 readily transmuted into ' inborn ' traits in the child. But Lamarck 

 first of all, or at least most consistently, gave scientific form to the 

 popular belief by allying it to a theory of evolution. His specula- 

 tions attracted little attention, even amongst students, till Darwin 

 and Wallace formulated their theory of Natural Selection. Subse- 

 quently, for a score or more of years, scientific thinkers, including 

 Darwin himself, believed that the organic world arose partly through 

 the * transmission ' of acquirements and partly through the natural 

 selection of favourable variations. During the last twenty years, 

 however, scientific opinion has veered to a conviction that Darwin 

 and Wallace, the most modest of men, worked better than they 

 supposed or rather than Darwin supposed, for Wallace has long 

 and consistently repudiated the Lamarckian doctrine. It is now 

 generally believed that acquirements are never ' transmitted,' and, 





