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.!. 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: (z) 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.? 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.* 
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. 
3 For discussion of “ Varieties ” see Walter, Genetics, pp. 60 f. 
4 Colvin and Bagley, Human Behavior, pp. 21-25, 126 ff.; Miller, Psychology 
of Thinking, pp. 18 f.; Parmelee, Science of Human Behavior, pp. 105 ff. 
