10 



THE EVOLUTION OE BIEDS. 



Use or 

 disuse. 



Limbs of 

 animals. 



Of the 

 humaa race. 



Natural 

 Selection 

 not a cause 

 of variation. 



Degradation 

 of the wings 

 of the Great 

 Auk. 



Thousands of facts can be adduced in support of this theory ; many are given by Darwin in 

 his wonderful book on the ' Origin of Species,' and others present themselves to the reader. 

 No better illustration of the effects of constant use in the development of the human frame 

 can be found than that of the extraordinary strength of muscle, and suppleness of limb, 

 which are acquired by acrobats trained from early childhood. Darwin gives an excellent 

 example of the double effect of use and disuse in his comparison of the domestic and the 

 wild Ducks. The Duck, when it has been domesticated for many generations, walks much 

 more, and flies much less than it did in a wild state. The consequence is that the wings of 

 the domestic Duck have grown less, and its feet larger. Darwin ascertained that the 

 difference was not confined to the flesh or the muscles, but that it extended even to the 

 bones. He found that the bones of the wings of the wild Duck weighed more than those 

 of the domestic bird, whilst exactly the contrary was the case in the bones of the legs and 

 feet. I once heard a well-known hatter say that high-priced hats were, on an average, 

 larger than low-priced hats, the only possible explanation being, that the men who wore 

 high-priced hats, and for the most part lived by their brains, had on an average larger 

 heads than those who wore low-priced hats, and for the most part lived by manual labour. 

 The statistics of the glove-maker, and the boot-makers, would doubtless be more striking, 

 though in the opposite direction, especially in the case of women's hands and feet, where 

 the difl'erence of use and disuse is greater. In none of these cases can Natural or Artificial 

 Selection have taken place. Darwin fully recognized the importance of the accumulated 

 results of use and disuse during many generations in modifying an organ ; but his reputation 

 is based upon the fact that he was the first writer who clearly showed the important part 

 which natural selection plays in increasing the rapidity with which these infinitesimally 

 small modifications may be accumulated, by the constant weeding out, in the struggle for 

 existence, of those individuals which lagged behind in the race. It must, however, always 

 be remembered that protective selection, or sexual selection, or selection of any kind is only 

 selection. It is not a cause of variation, it can only select from the variations that present 

 themselves such as are beneficial, and, by causing the possessors of the beneficial variation 

 to survive in the struggle for existence, transmit it to the next generation. 



The ultimate causes of variation are very subtle and difficult to trace. Why does an 

 organ grow larger or more perfect with use, and smaller or less perfect with disuse ? Is 

 it because the act of use sends blood and vital energy to the part used ? Did the wings 

 of each individual Great Auk fail to reach the dimensions attained by its ancestor because 

 it neglected the use of them during its minority ? And, if so, why did generation after 

 generation of Great Auks neglect to use their wings? Was it because there was no 

 struggle for existence ? Was food so plentiful that the assistance of its wings in diving 

 was unnecessary ? And was the Great Auk so powerful that it did not require to escape by 

 flight from its enemies until man arrived upon the scene ? It seems as if the ultimate 

 cause of the variation in the wings of the Great Auk, which finally caused the extinction of 

 the species, must be found in the inherited habits of the bird. It is difficult to imagine 

 how selection of any kind could have effected the modification. It can scarcely be sup- 



