INTRODUCTION 5 



is as yet far from that Evolution would be proved a some- 

 what less tardy process than Darwin supposed. 



Whatever be the rate at which Evolution proceeds, it is 

 quite clear that all structural changes, except of the most 

 trivial description, have sooner or later to submit to a severe 

 test. To this testing process Darwin gave the name of 

 Natural Selection. " Survival of the Fittest " suggested by 

 Herbert Spencer has the same meaning. 



That Natural Selection applies and must always have applied 

 to all forms of life was first recognised by Darwin and Wallace. 

 More organisms may be said to desire to live on earth and to 

 multiply than can be accommodated ; and which shall survive 

 must be determined by a principle of selection. In the in- 

 evitable struggle, all those forms which become the better 

 adapted to meet the difficulties and dangers that surround 

 them are the more likely to survive and leave posterity. The 

 fittest, in short, are selected by Nature for preservation, and 

 all advantageous variations in development receive encourage- 

 ment. In this way forms of life are slowly reconstructed, 

 reshaped, and recoloured ; and in course of time they become 

 so changed as to present a very different appearance from 

 that of their remote ancestors. Natural Selection, therefore, 

 in a sense, may be said to originate species. 



This selective system involving as it does a real progress 

 does not imply that organisms of inferior rank necessarily 

 cease to prosper as forms of higher rank are evolved. Or- 

 ganisms low down in the scale have proved well able to 

 contend with their conditions, whilst many superior forms 

 have failed, and disappeared without leaving descendants. 

 Small shrimp-like creatures that lived in Cambrian seas are 

 still represented by unmodified forms generically known as 

 Nebalia. Those little creatures, therefore, are seen in their 

 watery haunts to-day, reflected, as it were, from a remote 

 past. Certain lampshells also give us living pictures of 

 times long gone (Lingula). Moreover, minute one-celled 

 organisms are still through sea and land in their millions, 

 and billions, and myriads of them are probably not very 

 different from the forms in being when the world was young. 

 Whilst humble life-forms have thus continued their annals, 



