THE VITAL FABRIC OF DESCENT 3O7 



ORGANIC DESCENT A CONTINUOUS NETWORK. 



The normal individual diversity which has been destroyed by 

 inbreeding is not restored by mutation ; possibly it would reap- 

 pear if the different mutations were propagated in sufficient 

 numbers and allowed to intercross freelv ; but in domestication 

 they always suffer still further inbreeding.' Finally, even 

 crossing ceases to be effective for restoring the normal condi- 

 tion of intergraded individual diversity. Hybrids of inbred mu- 

 tations often follow closely the parental lines, and soon separate 

 again into the distinct types, as discovered by Mendel. It is 

 hoped by some to recombine these fag-ends of undone creation 

 into " new species," but this is to see Persian rugs in rag car- 

 pets, or oil paintings in three-color prints. 



A general misconception of the nature of evolutionary motion 

 has arisen because attention has been directed so largely to 

 domesticated species, in which descent has been limited to single 

 or very narrow lines. Phenomena of degeneration induced by 

 inbreeding have been interpreted very often as results of changed 

 environmental conditions. The mistake has been made of sup- 

 posing that evolutionary progress is a mere resultant of external 

 influences, whereas it is in reality a highly composite motion 

 carried forward in the intricate network of descent of the 

 normally interbreeding species. Natural selection forbids the 

 weaving of patterns discordant with the environment, but no 

 external influence actuates the loom. Nor need we allege any 

 other and more hypothetical force or agency as conducting the 

 change, the necessity of which is inherent, not in the individual 

 organisms as such, but in the association of diverse individuals 

 in interbreeding groups or species. If the physical basis of 

 this law of symbasis were understood the general fact of evo- 

 lution would also be comprehended as a natural and necessary 



' The abnormal amplitude of mutational variations has been likened in an- 

 other place to the unusual fluctuations of temperature in disease. The abnor- 

 mality is in the conditions ; mutations may be of the same essential nature as 

 normal variations, into which they seem to grade as insensibly on the one side 

 as they do into obvious monstrosities on the other. Professor DeVries has ex- 

 plained that he gave Oenotkera lamarckiaiia special attention in his search for 

 mutations because it was " rich in monstrosities." DeVries, 1905, A New Con- 

 ception of the Origin of Species, Harper's Magazine, no: 212. 



