THE CAUSATION OF DISEASE. 85 



the fixity of what we may term racial, as distinguished from 

 individual, peculiarities, this does not, perhaps, altogether result 

 from the mere fact that a peculiarity has been repeated during 

 many generations. This repetition may not be the cause, but 

 the result, of a fixedness which is independent of repetition ; 

 for many species have, on domestication, more or less readily 

 lost characters which they retained during countless ages in the 

 wild state; and, in many cases, at all events, there "does not 

 appear to be any relation between the force with which a char- 

 acter has been transmitted and the length of time during which 

 it has been transmitted." * Nevertheless, although certain 

 characters of great ancestral age readily disappear under an 

 altered environment, we shall find the principle above enunciated 

 to be on the whole a safe one. Darwin thus expresses his 

 conclusion upon this head : " Notwithstanding these considera- 

 tions, it would perhaps be rash to deny that characters become 

 more strongly fixed the longer they are transmitted ; but I believe 

 that the proposition resolves itself into this, — that characters of 

 all kinds, whether new or old, tend to be inherited, and that 

 those which have already withstood all counteracting influences 

 and been truly transmitted, will, as a general rule, continue to 

 withstand them, and consequently be faithfully transmitted." f 



A consideration of the embryonic changes would appear 

 to afford a proof that repetition does actually fix a character. 

 The early developmental changes of the embryo date back 

 through millions of generations, and by incessant repetition 

 have become rigidly fixed. In this way many remote ances- 

 tral characters, such as the branchial clefts, appear. It is true 

 they soon vanish, but they are nevertheless fixed in the race, 

 for they have in this way appeared during untold generations, 

 and probably will continue to do so as long as man exists. But 

 although many remote ancestral characters are thus retained, 

 how great is the number that have been dropped ! Charac- 

 ters which have been present during hundreds and thousands, 

 nay, perhaps, even millions of generations, alike with such as 

 have lasted for a few generations only, have thus been gra- 

 dually lost, as the organism has become moulded to an ever- 



* "Variation under Domestication," vol. ii. p. 38. 

 •f Ibid., vol. ii. p. 39. 



