INDIRECT IMPORTANCE OF MODIFICATIONS 243 



priate environment is the necessary correlate of a normal in- 

 heritance, otherwise the organism cannot realise itself in de- 

 velopment ; (2) that changes in environment and function may 

 provoke variations in the germ-plasm ; (3) that the individual 

 is often very plastic and readily acquires adaptive modifications 

 which may be of great individual importance, and may even 

 preserve the life ; (4) that the secondary effects of modifica- 

 tions may, in certain cases, reach and influence the germ-cells ; 

 (5) that the state of the maternal constitution is very important 

 in cases where there is an intimate connection between the mother 

 and the unborn young. 



Selection and Stimulus. — In two other ways changes in the 

 conditions of life are of great importance : they form part of 

 the mechanism of selection, whereby the relatively less fit 

 variants are quickly or slowly, roughly or gently, eliminated ; 

 and they act as a stimulus to the intrinsic self-assertiveness and 

 " endeavour after well-being " which characterise living crea- 

 tures. We must advance beyond the conventional view that 

 the environment is like a net closing in upon passive victims, 

 which can only escape if they have been fitted by germinal varia- 

 tion (or acquired modification) to pass through some of the 

 meshes ; we must recognise as a fact of life, what Lamarck and 

 many others have seen with clearness, that organisms actively 

 assert themselves against this closing net, and by active en- 

 deavour (also, of course, a variational character when traced 

 back) may win their way through. 



Indirect Importance of Modifications. — But there is another 

 important consideration, which has been stated independently 

 by Profs. Mark Baldwin, Lloyd Morgan, and H. F. Osborn — 

 namely, that adaptive modifications may act as the fostering 

 nurses of germinal variations in the same direction. We have 

 referred to this elsewhere, but it may give greater completeness 

 to our survey if we quote a brief statement of the idea as ex- 

 pounded by Lloyd Morgan {Habit and Instinct, 1896, p. 319) : 



