37S THE GRAMMAR OF SCIENCE 



are compelled to turn to environment for our causal 

 relationship. Now this environment may be either in- 

 organic or organic. If organic, it may be either of the 

 same type or another type. We have then the following 

 sources of change in living forms possible : — 



(a) Change due to inherent tendencies in the individual 

 or to batJimic ittfluence. 



ib) Change due to other individuals of the same living 

 type or to aiitogeneric influence. 



{c) Change due to other living types or to heterogeneric 

 influence. 



id) Change due to physical environment or to inorganic 

 infiue^ice. 



Ultimately the physical environment (p. 374) may have 

 determined all types of life, and so the heterogeneric 

 influencebe ultimately traceable to inorganic influence. Now 

 realising the existence of death, we see that no change in 

 any form of life could be progressive unless each step of 

 that change were handed on to the next generation. 

 Materially by the next generation having like organic 

 modifications ; mentally by the transmission of customs, 

 institutions, knowledge. The latter mode is, as a rule, 

 only possible where one generation survives and lives for 

 a time, at any rate, a common life with a second.^ The 

 two modes are respectively spoken of as inheritance and 

 tradition. Diverse as these two modes appear, it is yet 

 often doubtful whether a habit is to be attributed to 

 instinct, — i.e. to inheritance, — or to tradition, especially 

 among gregarious animals."' But without one or other 



1 A community of human beings, say 1 8 years of age, if isolated on an 

 island and separated from all civilisation, might if tradition could be destroyed 

 still survive, or certain members might survive ; the type of life, however, 

 would undoubtedly be immensely modified, even if in course of time new 

 traditions were evolved. Habit, custom, tradition, help to create the en- 

 vironment. 



^ There is too great a tendency to attribute to instinct in the lower types of 

 life what is assigned to tradition in the case of man. Has tradition no part in 

 the migration of birds? When T meditates, he always twists a curl behind 

 his left ear with his forefinger ; his uncle, I find, has precisely the same 

 habit. Two brothers, A and B, have developed in mid-life a trick of 

 stroking an eyebrow ; their father C, who died when they were young boys, 

 did the same thing. Their mother D in extreme old age mistook her son A 



