7 i The Outline of Science 



growth and others rapidly alter the pressure and composition of 

 the blood. Some of them call into active development certain 

 parts of the body which have been as it were, waiting for an 

 appropriate trigger-pulling. Thus, at the proper time, the milk- 

 glands of a mammalian mother are awakened from their 

 dormancy. This very interesting outcome of evolution will be 

 dealt with in another portion of this work. 



THE INCLINED PLANE OF ANIMAL BEHAVIOUR 



Before passing to a connected story of the gradual emerg- 

 ence of higher and higher forms of life in the course of the 

 successive ages the procession of life, as it may be called it will 

 be useful to consider the evolution of animal behaviour. 



Evolution of Mind 



A human being begins as a microscopic fertilised egg-cell, 

 within which there is condensed the long result of time Man's 

 inheritance. The long period of nine months before birth, with 

 its intimate partnership between mother and offspring, is passed 

 as it were in sleep, and no one can make any statement in regard 

 to the mind of the unborn child. Even after birth the dawn of 

 mind is as slow as it is wonderful. To begin with, there is in the 

 ovum and early embryo no nervous system at all, and it develops 

 very gradually from simple beginnings. Yet as mentality cannot 

 come in from outside, we seem bound to conclude that the 

 potentiality of it whatever that means resides in the indi- 

 vidual from the very first. The particular kind of activity known 

 to us as thinking, feeling, and willing is the most intimate part 

 of our experience, known to us directly apart from our senses, and 

 the possibility of that must be implicit in the germ-cell just as the 

 genius of Newton was implicit in a very miserable specimen of 

 an infant. Now what is true of the individual is true also of the 

 race there is a gradual evolution of that aspect of the living 



