190 The Mechanism of Etoltttion in Leptinotaesa 



jumps or not, and whether they are qualitative or quantitative in character. If 

 the gene be so independent and have a mean about which common differences 

 fluctuate, a different conception than is current of those of inorganic bodies 

 must be formed of organic attributes. 



Heterogeneity is, of course, the sole basis of evolution, is evolution at work, 

 and the processes which follow are entirely of conservation to preserve, rearrange, 

 and distribute among organic bodies the changed and new attributes presented. 



CAUSES OF HETEROGENEITY. 



The causes of heterogeneity are certainly diverse, but appear in two main 

 groups of causation: First, transmutation in the qualities with subsequent 

 adjustments in the attributes and conditions of organisms; and second, diversity 

 resulting from recombinations (metathesis) . 



The opinions concerning the causes of transmutation current with Darwin and 

 his co-workers placed much weight upon the conditions of life as efficient forces 

 for initiating change. This was, however, not much more than opinion and 

 not at all the product of exact investigations. The Weismannian hypothesis 

 also considered the conditions of existence as the essential force in the produc- 

 tion of change, but placed the process in a different setting ; but the principle was 

 the same — the stress of conditions produced either increase or decrease in the 

 qualities and attributes of the living substance. Some difference of opinion as 

 to how this came about existed, all of hypothetical character and not of any mo- 

 ment here. All saw that in some way there must come to exist in the germ 

 something to give expression to the changed character in subsequent generations. 

 Arguments concerning this method have in the main revolved around the 

 origin peripherally, and the aggregation in the germ, or of the origin directly in 

 the germ and subsequent manifestation in ontogeny. Opinions have differed and 

 still differ with respect to these problems, but in the last decade researches show 

 concretely that transmutations may arise through the direct action of incident 

 forces upon the germ, and that action upon the soma has not produced inherit- 

 able changes. These investigations serve in some measure to clarify a much- 

 befogged situation. Clear, consistent proof is provided of the alteration in the 

 germ of that something which conditions a character in the soma, and the evi- 

 dence available strongly indicates that the changes found are not the product of 

 a struggle between determinants, but changes which appear suddenly, are fixed 

 from the start, and are physico-chemical in character, and not the outcome of a 

 struggle for place and food between lesser organic units. 



It is certain that the action of incident conditions is a potent force in trans- 

 mutation phenomena, but whether it is the only productive force remains to be 

 proved. Many are of the opinion that purely internal operations are in con- 

 siderable measure responsible for evolution, if not entirely. These automatic 

 internal conditioning and determining forces are dangerous concepts for the 

 biologist. If organisms are conceived of as automatic, internally regulated and 

 propelled mechanisms, they are the only self-contained mechanism in existence, 

 all others depending upon the interplay between the mechanism and external 

 forces for their operation. Even if it be admitted that organisms are automatic, 

 they would, unless possessed of an " inherent tendency to vary," go on in per- 

 petuity in the same form and condition. Inherent tendencies of any kind are 



