150 Terminology and Criticisms 



may chance to have, and also allow further variations in 

 the same direction. In any given series of generations, the 

 individuals of which survive through their susceptibility 

 to modification, there will be a gradual and cumulative 

 development of coincident variations under the action of 

 natural selection. The individual modification acts, in 

 short, as a screen to perpetuate and develop congenital 

 variations and correlated groups of these. Time is thus 

 given to the species to develop by coincident variation 

 characters indistinguishable from those which were due to 

 acquired modification, and the evolution of the race will 

 proceed in the lines marked out by private and individual 

 accommodations. It will appear as if the modifications were 

 directly inherited, whereas in reality they have acted as 

 the fostering nurses of congenital variations. 



It follows also that the likelihood of the occurrence of 

 coincident variations will be greatly increased with each 

 generation, under this 'screening' influence of modifi- 

 cation ; for the mean of the congenital variations will be 

 shifted in the direction of the individual modification, see- 

 ing that under the operation of natural selection upon each 

 preceding generation variations which are not coincident 

 [or correlated] with them tend to be eliminated.^ 



Furthermore, it has recently been shown that, inde- 

 pendently of physical heredity, there is among the animals 

 a process by which there is secured a continuity of social 

 environment, so that those organisms which are born into 

 a social community, such as the animal family, accommo- 

 date themselves to the ways and habits of that community. 

 Professor Lloyd Morgan,^ following Weismann and Hud- 



1 This aspect of the subject has been emphasized in Chap. X., above. 



2 Introduction to Co7nparative Psychology, pp. 170, 210, and Habit and 

 Instinct, pj). 183, 342. 



