THEORIES OF EVOLUTION 15 



butting ; which irritated the periosteum on certain portions 

 of the frontal bone; which produced bosses of bone on 

 the irritated spots; which, by the accumulation of effects 

 during generations, evolved at last into the great branch- 

 ing structures we know. It supposes that the ox and the 

 rhinoceros have horns and the cock and the crested screamer 

 (Palamedea cornuta) have spurs because analogous causes 

 irritated certain portions, not of the periosteum, but of the 

 epidermis. It supposes that the descendant of many 

 generations of blacksmiths will be stronger physically but 

 weaker mentally than the descendant of many generations of 

 students. It supposes that the conditions which produce 

 health and strength in a succession of parents absence of 

 pathogenic agencies, sufficient exercise, abundance of suitable 

 food and fresh air, the right degree of moisture and tempera- 

 ture, and so forth will ultimately render the race strong, 

 hardy, and vigorous ; whereas contrary conditions will render 

 it feeble. 



26. We need not multiply instances; the Lamarckian 

 doctrine should now be plain to the reader. It is necessary 

 however to note a few additional points: (a) Just as the 

 doctrine of the transmission of acquirements is not adequate 

 to explain all the facts of heredity, so, also, it is not adequate 

 to explain all the facts of evolution ; for example, while it is 

 perhaps competent to explain man's intellectual powers or 

 the antelope's speed, it cannot explain why man has long 

 hair on his face, which is lacking in woman, or why the 

 colours of one species of antelope differ from those of another. 

 Neither man nor antelopes make acquirements with respect 

 to hair or colour except such as lead to the loss of them. It 

 cannot explain the differences in integuments of the different 

 species of fish. It can explain hardly a single fact in the 

 whole world of plants. In fact, however simple and fascin- 

 ating the Lamarckian doctrine may appear at first sight, 

 however well it may seem to explain certain phenomena, it 

 is quite insufficient to explain the totality of phenomena. 

 It may possibly be accepted as a partial explanation of 

 evolution ; it cannot be accepted as a complete explanation. 

 (6) Again it must be noted that the Lamarckian hypothesis 

 is not only a doctrine of evolution but also one of degenera- 

 tion ; it supposes that all beneficial agencies which act on a 

 species are causes of evolution, whereas all injurious agencies 

 are causes of degeneration. In this, as we shall see presently, 

 it is in violent and fundamental opposition to the Darwinian 

 explanation, (c) Yet again it must be noted that, if the 



