INDIVIDUAL AND ANCESTRAL DEVELOPMENT 317 



Cell-differentiation is neither inherent in germ-cells nor induced 

 by the conditions of existence, because it is in the reciprocal inter- 

 action between them. They who seek it in germ-cells or in chro- 

 matin forget that these are not self-sufficient entities, but parts 

 of the natural world. They who seek it in the conditions of exist- 

 ence forget, or fail to perceive, that development is a preparation 

 for a test that is to come later in the struggle of life. 



The reciprocal interactions that are characteristic of normal de- 

 velopment are of a very peculiar sort. They are not merely actions 

 and reactions, but responses or answers, and I ask you to consider 

 what this word means, because experimentalists often content 

 themselves with a very imperfect concept of its meaning. 



If I kick a dog, his actions are not ordinary reactions. They are 

 preparations for meeting the further violence of which the kick is 

 a warning. Events do not take place anyhow and at random in 

 nature. They are so related to each other that each is a sign of 

 others that may be expected in course of nature, and for which 

 scientific knowledge helps us to prepare, but it is the preparation, 

 and not consciousness of it, that is useful. When a chick hears the 

 warning cry of the hen it runs to her for protection from the threat- 

 ened danger, although it may not know the source of danger, nor 

 even what danger is. There is a relation, external to the chick, 

 between the warning cry and threatened danger, and the effect upon 

 its bodily machinery of the warning is an act which is suited for 

 escaping the danger of which the warning is the sign. Since the 

 danger is not discoverable in the structure of the chick, experiment- 

 alists are apt to ignore this characteristic of responses, that which 

 makes them responses and not ordinary reactions; but neither the 

 warning cry nor the danger is to be found in the chick, yet the 

 stimulants which bring about vital responses are thought worthy 

 of study. The ability of the chick to make responses does not re- 

 strain it from aimless or injurious acts. Its fitness is not abstract 

 or metaphysical, but practical. It may escape danger by means of 

 its mother's warning, or it may be drawn into danger by an imita- 

 tion of it, but the bird that falls into the net of the fowler is blotted 

 out of history. Natural selection is not an agent who does things, 

 but a general word for formulating the struggle of each individual 

 for existence, and the survival of the fittest. There is nothing 

 general or abstract in this struggle, for it is preeminently private 

 and particular. We speak of the struggle for existence; but my 

 struggle has not been like yours, and the struggle for existence is 

 only a formula. Species have come about according to but not 

 because of or by means of the principle of the survival of the fittest, 

 for a formula can do nothing. The fitness of living beings is not 

 ideal or abstract, but private and particular. We say an animal is 



