288 THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 



(or acquired), in contradistinction from variation, which is of germinal origin (or congenital). 

 Organisms capable of extensive modification are termed plastic; and this Plasticity (q. v .) may be 

 subject to selection. The term Accommodation (q. v.) is reserved by some writers for the moulding 

 of behavior to environing circumstances on the part of organisms, referring to function rather than 

 to structure. On the hypothesis of Organic Selection (q. v.) modifications of structure may serve to 

 foster Coincident Variations (q. v.) of like nature, and accommodations of behaviour may thus set 

 the direction of congenital variation, and so of evolution under the action of natural selection. 



Literature: Lloyd Morgan, Habit and Instinct; J. Mark Baldwin, A New Factor in Evolution, 

 Amer. Natural., June-July, 1896; Headley, The Problems of Evolution (1901). [Dictionary of 

 Philosophy and Psychology, vol. II., The Macmillan Company, 1902, p. 94.] 



If we thus review ontogeny we are impressed, first, with the fact that it is 

 the visible expression of heredity; second, that its range is enormous; third, that 

 it is constantly inseparable from the other three factors, heredity, environment, 

 selection. The opportunities for the initiation or origin of new characters in 

 ontogeny is also very great through direct action of environment and actively 

 in all those parts which depend upon movement for their development. 



All species and varieties in the plastic or modifiable parts of their organization 



are in a sense ontogenic. 



If the sum of changes involved in ontogeny is normal or typical, the individual 

 (unless abnormal through heredity or environment) is normal. Any abnormality 

 in the sum of changes involved in ontogeny may produce an abnormal, or atypical 



individual. 



There is in a sense, therefore, an evolution of the soma under a discontinuous 



ontogeny and discontinuous environment which is quite distinct from the 



continuous evolution of the blastos. 



There is in all organisms more or less disharmony, or dysteleology between 

 the evolution of the soma and the evolution of the germ; the former is in many 

 respects more progressive, the latter more conservative. 



The following general observations and points may be made partly in recapit- 

 ulation of the above. These points are suggestive of experiment and of further 

 inquiry. 



1. Ontogeny is not separable from heredity; it is to be regarded as the 

 expression of heredity as reaching to and modified by the conditions of lite, 

 of environment and of selection. Ontogeny results in the sample organism 

 which is put to the test of selection. 



2. Thus normal, or typical ontogeny, t. e., repetition, is dependent on typical 

 heredity, typical activity of the organism, typical organic or inorganic environ- 

 ment, undisturbed social relations and undisturbed incidence of selection. Thus 

 ontogeny affords a complete illustration of the inseparable factors of life. 



3. Atypical ontogeny is caused by the same relations in abnormal form. 



4. Further, ontogeny is a test of heredity since it involves a process o 

 internal elimination and selection, or approval of the changes offered by heredity. 



5. We express in the terms "variability," "modifiability," "plasticity ^ 

 adaptability," etc., the powers of the organism to readjust itself to new cir- 

 cumstances. 



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