200 Causes and Course of Organic Evolution 



The first of these occurs when the integrating agencies as 

 a whole are practically balanced by the disintegrating, alike 

 in the individual up to the period when reproduction has been 

 effected, and in its progeny through successive generations. 

 In this case the continuously regenerated group of individuals 

 that makes up the species will remain unaltered. This is the 

 condition that applies to by far the largest number of indi- 

 viduals of any species, when studied at any one place amid 

 like environal surroundings, and not through long continued 

 periods of time or over wide and varied areas. 



It was this fundamental and exact similarity in millions of 

 individuals that had intercrossed over wide expanses of country 

 that caused the earlier systematists to believe in species-im- 

 mutability. Only as the world was ransacked and viewed 

 by observant naturalists like Lamarck, Darwin, Hooker, Wal- 

 lace, Mueller, and others before or since, did the idea of species- 

 mutability dawTi, and the causes for it become discussed. Then 

 since "extermination" stood out as an apparent and universal 

 cause for disappearance of the connecting links, selective sur- 

 vival stood out as a dominant factor in the minds of many 

 evolutionists. It is to the lasting credit of Lamarck that he 

 looked beneath the surface struggle, and recognized environ- 

 ment as a potent cause of change, and often even directly 

 of extinction. 



But when one reflects on the profound and extensive balance, 

 and yet continuance, of existence that may prevail for thousands 

 or it may be millions of years between species-organisms and 

 the environal agents around, one realizes how complicated may 

 be the factor of Selection, even though of subsidiary value to 

 the other three. So a balanced selective survival — or pan- 

 mixia of Weismann — usually represents accessory or collateral 

 combinations of conditions that the three factors, heredity, 

 environment, and i)roenvironment, have largely established. 

 Though less active then as an originating cause, it may effect 

 long persistence of individuals and of a species, if environal 

 conditions remain imiform. 



The second exhibition of Selection, that we have called pro- 

 gressive advance, differs from the last in that combinations 



