282 FOOT-NOTES TO EVOLUTION. 
organism” must break down sooner or later, man not 
less than others. Senility brings even to the best some 
form of nerve decay. The wisest man 
must come to second childhood. Senil- 
ity may come prematurely as a result of 
influences adverse to mental and 
physical activity. These influences 
are manifold and the enumeration 
Degeneration of 
senility. 
4 
| 
Fic. 25.—Sacculina attached" Fic. 5 — Gace with 
to the crab. limbs absorbed. 
of causes and results of the weakness of old age need 
not be attempted here. 
Race degeneration, or continuous decline from gen- 
eration to generation, may be distinguished from the 
wearing out of the individual. , The for- 
mer results from the continuous preser- 
vation of the unfit. As the destruction 
of the unadapted is the chief element of race progress, 
so is their survival the chief element in race decay. De- 
generation occurs when weakness mates with weakness; 
Race 
degeneration. 
