NATURAL SELECTION 149 



Evolution by Natural Selection is evolution brought about Summary 

 by chance coincidences, chance hits, variations in the species 

 happening to suit some feature of the environment. But from 

 the very earliest stage the range of variation possible is limited 

 by heredity, and as evolution proceeds it is still further narrowed. 

 Similarly the environment (or at least the environing species of 

 which it mainly consists) has, as a rule, been evolved part passu y 

 and its range of variation is limited by the same principle. Thus 

 heredity decides vaguely for the species what its future is to be. 

 The environment itself evolved side by side with the species 

 on parallel lines, so that there is likely to be further parallelism 

 decides definitely. 



Thus there is chance, but chance within certain limits on 

 either side, in the species and its environment. This limita- 

 tion, makes the lucky coincidences, which we call adaptations, 

 intelligible. They are often facilitated by the fact that there are 

 alternative environments or alternative methods of adjustment to 

 the same environment, //// the organism has adopted a particular 

 method of suiting itself to its conditions. 



I will now recall the conclusion arrived at in the previous section. 



Chance does not decide in what environment the young of a 

 species shall place themselves. Among the lower classes of 

 animals there is instinct as a guide. Higher up, parents first 

 make a sheltered environment for their young, then in many 

 cases direct them to the environment best suited to their years 

 of maturity. They intervene to save the next generation from 

 the tender mercies of chance. Among social species the same 

 principle is carried further. 



As evolution proceeds, therefore, chance works within ever 

 narrowing limits. 



, 



IX 



CONSCIOUSNESS 



When one has realised all that embryology has to tell, and 

 when one has seen how the various classes of animals may be 

 arranged in a genealogical tree on a system suggested by the 





