64 THE FOUR SEGREGATIVE PRINCIPLES. 



escaped by remaining in the cliffs.* These forms of selection are im- 

 posed on itself by the forms of accommodation the species has assumed, 

 for the conditions are not so determined by the environment that no 

 alternative remains to the organism. The cliff swallow might still 

 build its nest in the cliff. The selection to which it is exposed is 

 determined by the choice of the bird between alternatives afforded by 

 the environment, and may therefore be called endonomic selection. 



9. Endonomic and Coincident Selection Illustrated by the Survival of 

 Infants Fed on Substitutes for Mother' s Milk. 



Not only arc previous forms of cnvironal selection brought to an end by 

 accommodation, but certain forms of reflexive selection may be thus 

 made to cease, and perhaps other forms introduced. From the era when 

 the mammalian class first arose till comparatively recent times, every 

 mammalian mother that failed to give milk also failed of raising her 

 young; and so the propagation of a stock seriously deficient in this 

 respect was rigorously prevented by filio- parental selection. How- 

 ever, amongst human mothers such cases occasionally arise; and, 

 amongst civilized races, the provision for the young thus deprived of 

 their natural nourishment is so complete that they are placed at no 

 disadvantage. This form of filio-parental selection, which has been in 

 full force for countless ages, now ceases for civilized man. Among half- 

 civilized races the substitutes for the mother's milk vary with each 

 nation, and the original filio-parental selection is supplanted by a form 

 of social selection ; for the article used as a substitute is determined 

 by tradition, and the material furnished is so deficient in the needed 

 qualities that a proportion of the infants are unable to survive on such 

 food. The survivors are, therefore, determined by endonomic selec- 

 tion. They are selected on account of their being better endowed for 

 meeting the ordeal of feeding on the substitute provided by the tra- 

 dition of the community. But it is also an example of coincident selec- 

 tion ; for if accommodation had not come in to aid in the process all 

 infants whose mothers failed to give milk would have perished. On 



* I am informed by Prof. Lynds Jones, of Oberlin College, that several birds of 

 North America have passed through a similar transformation of their habits. 

 Besides the cliff swallow just mentioned, which attaches its nest to the overhang- 

 ing eaves of a house instead of plastering it against the roof of a cave or hole in 

 the cliff, there is the barn swallow, which usually attaches its nest to the rafter of 

 a barn, also the chimney swift (referred to in the early part of this section), that 

 used to build in hollow trees. The tree swallow and the house wren are two 

 species that are still in a transition state in their habits, for many of them avail 

 themselves of bird-boxes or of holes and snug nooks about houses, while others 

 prefer holes in trees and stumps, as in better accord with old and safe traditions. 



