AN ESSAY ON LONGEVITY. 89 



whilst he grows feebler in limb, unproductive as a 

 labourer, impotent as a warrior, in all such regards a 

 mere burden on the species, yet the knowledge and 

 experience stored in his great brain is of use to his 

 younger fellow-men, and age is for that reason re- 

 spected. Moreover, the species Homo is widely dif- 

 ferent from any other species ; indeed, from the point 

 of view of a general philosophy, it is almost erroneous 

 to apply the term ' species ' to the collective varieties 

 of man ^ at all. For the development of the brain 

 and of intelligence in man has really changed the 

 whole course of Nature, supposing that the develop- 

 mental course was hers. The further progress of 

 organic beings beyond the limit reached by man 

 (and this may be as acceptable a truth to the teleo- 

 logist as to the evolutionist) can only operate through 

 that brain, so thoroughly dominant, so all-powerful 

 has it become. No longer are the structures of the 

 whole organism affected by changed conditions, but 

 of the brain alone,^ and the result of this is that 

 there are no physiological species among men. The 

 various races and kinds of men can interbreed. It is 

 only their intelligence, their power, knowledge, and 

 cast of thought which largely differs, and this does 



' The term ' polymorphism ' is fairly applicable,' in its zoological 

 sense, to man as a civilized being, each unit in a society, with his 

 special skill and special function, being comparable to such units in a 

 polypidora or a hymenopterous colony. 



^ Other changes are exceedingly small, and are not permanent as are 

 those of the brain. 



