78 ADAPTATION AND PROGRESS 



maimed and the "drones"; sometimes, however, it seems to 

 manifest itself in defence of the helpless and weak, thus providing 

 the biological background of " mutual aid " in the social behavior 

 of men. 1 But the range of mal-adaptation possible before 

 elimination takes place is often wide, 2 — and here again the 

 decisive factor is the severity of the struggle for existence, and 

 although adaptation in the strict use of the term and in every 

 particular may not be necessary to the mere existence of the 

 individual to the point of reproduction and so to the point neces- 

 sary for the preservation of the species, adaptation in this sense 

 is necessary for the largest possible life of which any individual 

 or species is capable. The pine tree of the tropics is vastly dif- 

 ferent from the pine tree of the cold regions. 



Permanent modifications within a species, as in the forma- 

 tion of new varieties seem to come: (i) as a result of inter-cross- 

 ing; (2) through a great change in the environment affecting a 

 certain portion of the species eliminating all but those whose 

 variations from the type prove best adapted to the new conditions 

 of life; (3) through geographical isolation resulting in inbreeding 

 and the selective pressure of a different combination of environ- 

 mental conditions, or (4) by spontaneous variation or mutation 

 often with the potency of development, arising by a process as yet 

 unknown. 3 When the changes are sufficiently great, especially 

 when the reproductive functions are affected so as to make the 

 individuals of the variety and the parent species infertile when 

 crossed, we have a new species. 



As tropisms, reflexes and instincts are inborn characters, or 

 based on such, their origin is to be explained in accordance with 

 the above principles, and they are to be considered as on the 

 whole of adaptive value either to the individual or to the species. 4 

 They may persist, however, as " vestiges " even though disuseful, 

 providing this disutility is not sufficient to lead to elimination. 



The human organism is in direct descent from the anthropoid 

 apes or from the common precursor of these and man, and the 



1 Kropotkin, Mutual Aid. 2 Kellogg, op. cit., p. 227. 



* For discussion of " Varieties " see Walter, Genetics, pp. 60 f. 

 4 Colvin and Bagley, Human Behavior, pp. 21-25, 126 ft; Miller, Psychology 

 of Thinking, pp. 18 f.; Parmelee, Science of Human Behavior, pp. 105 £f. 



