120 GEOLOGICAL BIOLOGY. 



Ancestry and Environment in Relation to the Beginning of Each 

 Individual. From this point of view we recognize two classes 

 of phenomena which are all-important factors in determining 

 the particular form and structure of every organism, and the 

 fundamental difference between the two groups is found in 

 the relation they bear to the beginning of the development of 

 each individual. The one set of conditions have exerted their 

 effect when the first germ of the new individual arises, and 

 to them is applied the general name Ancestry. The other set 

 begin to influence the individual only after development has 

 begun, and to this set of conditions the general term Environ- 

 ment is applied. Evolution is the name given to the results, 

 in structure and function of organisms, which are traced to 

 Ancestry and Environment as determining causes. 



It is from this philosophical point of view that the follow- 

 ing definitions become appropriate : 



Definition of the Terms " Ancestry" and " Conditions of Environ- 

 ment." Ancestry, as defined in the Century Dictionary, is 

 " the series of ancestors, or ancestral types, through which an 

 organized being may have come to be what it is in the process 

 of Evolution;" and in the same work the term conditions of 

 environment is defined as " the sum of the agencies and 

 influences which affect an organism from without ; the 

 totality of the extrinsic conditioning to which an organism is 

 subjected, as opposed to its own intrinsic forces, and there- 

 fore as modifying its inherent tendencies, and as a factor in 

 determining the final result of organization. It is an expres- 

 sion much used in connection with modern theories of evolu- 

 tion in explaining that at a given moment a given organism 

 is the resultant of both intrinsic and extrinsic forces, the latter 

 being its conditions of environment and the former its in- 

 herited conditions."* Ancestry and Environment are, in 

 the abstract, names for these intrinsic and extrinsic factors of 

 evolution. 



If we examine only the paleontological series, we might 

 conclude that the course of evolution was determined entirely 

 by the first set of conditions, Ancestry ; and, on the other 



* Century Dictionary, vol. I. pp. 201 and 958. 



