12 THE PRINCIPLES OF HEREDITY 



20. At first sight it would appear an easy matter to test 

 the truth of the Lamarckian doctrine of heredity. We might, 

 for example, amputate the tails of a pair of parent dogs, and 

 then observe whether the puppies, subsequently born, were 

 tailless. But the theory is not held in this crude form, at 

 any rate by the scientific supporters of it. They assume that 

 acquirements are only " faintly " and " fitfully " 1 transmitted, 

 a reservation which makes any direct test extremely difficult. 

 Decisive proof or disproof can be obtained only by observing, 

 on the one hand, whether races or species possess characters 

 the existence of which is explainable only on the Lamarckian 

 doctrine of heredity ; or, on the other hand, whether they 

 possess characters the existence of which is incompatible with 

 the truth of it in other words, we must seek conclusive 

 evidence in the changes undergone by races, not in those ex- 

 hibited by individuals. This test, indeed, must be applied to 

 every doctrine of heredity ; for, while the variations of indi- 

 viduals admit, generally speaking, of explanation by a number 

 of theories of heredity, the changes undergone by races 

 admit of explanation, as we shall see, by only one. 



21. Three well-known doctrines of racial change, or rather 

 of evolution (adaptive racial change), have been formulated : 

 the Lamarckian, which attributes evolution to the trans- 

 mission of acquirements ; the Darwinian, which attributes it 

 to Natural Selection ; and the Bathmic, which attributes it 

 to an "inherent adaptive growth -force." Each of these 

 doctrines of evolution is founded on a special doctrine of 

 heredity, and, since doctrines of heredity cannot be adequately 

 tested except by the evidence afforded by racial change, our 

 next endeavour must be to gain a clear conception of each 

 of these three theories of evolution. 



1 Romanes, Darwin and After Darwin, vol. ii., p. 152. Cf. also An 

 Examination of Weismannism, p. 6. 



