THE DARWINIAN THEORY 55 



Natural selection can also bring about changes at every age, 

 for the elimination of individuals begins from the e^g, and any kind 

 of egg which is in some way better able to escape elimination 

 will transmit its useful characters to its descendants, because the 

 resulting young animals will thus more frequently reach full develop- 

 ment than the young from other eggs. In the same way, at every 

 succeeding stage of development, every character favourable to the 

 preservation of the individual will be maintained and intensified. 



We see from all this that natural selection is vastly more 

 powerful than artificial selection by Man. In the latter, only one 

 character at a time can be caused to change, while natural selection 

 may influence a whole group of characters at the same time, as 

 well as all the stages of development. Through the weeding out 

 of the individuals which are annually exterminated, it is always 

 on an average the ' fittest ' which survive, that is to say, those which 

 have the greatest number of bodily parts and rudiments of parts 

 in the fittest possible condition of development at every stage. The 

 longer this process of selection continues, the smaller will be the 

 deviations of the individual from this standard, and the more minute 

 will be the ditferences of fitness determining which is to be eliminated 

 and which is to survive to reproduce its characteristics. In the 

 immeasurable periods of time which ai<§ at the disposal of natural 

 selection, and in the inestimable numbers of individuals on which 

 it may ojoerate, lie the essential causes of superiority of natural 

 selection over the artificial selection of Man. 



To sum up briefly : Natural selection depends essentially on 

 the cumulative auofmentation of the most minute useful variations 

 in the direction of their utility ; only the useful is developed and 

 increased, and great eftects are brought about slowly through the ^ 

 summing up of many very minute steps. Natural selection is a self- 

 regulation of the species which secures its preservation ; its result 

 is the ceaseless adaptation of the species to its life-conditions. As soon 

 as these vary, natural selection changes its mode of action, for what 

 was previously the best is now no longer so ; parts that before had to 

 be large must now perhaps be small, or vice versa; muscle-groups 

 which were weak must now become strong, and so on. The con- 

 ditions of life are, so to speak, the mould into which natural selection 

 is continually pouring the species anew. 



But the philosophical significance of natural selection lies in 

 the fact, that it shows us how to explain the origin of useful, well- 

 adapted structures purely by mechanical forces and without having 

 to fall back on a directive force. We are thus for the first time in 



