188 DISCOVERY CH. 



characteristics postulated by it has yet to be accepted 

 at the bar of scientific opinion. 



Lamarck grasped the truth of organic evolution 

 better than any naturalist who preceded him, and he 

 carried out the principle on a far larger scale and in 

 greater detail than others had done, but his arguments 

 were not convincing. It was reserved for Charles 

 Darwin and Alfred Russel Wallace to import into the 

 problem an entirely fresh set of considerations, and to 

 establish a new and illuminating theory upon a secure 

 basis of fact. 



As naturalist on H.M.S. Beagle during a five years' 

 voyage round the world, thrown upon his own mental 

 resources and furnished with many new and interesting 

 facts, Darwin was early confronted with many sides of 

 the process of evolution upon which to exercise his 

 imaginative and reasoning powers. The solitude of the 

 voyage and the almost continuous ill-health afterwards 

 " For forty years he never knew one day of health " 

 were contributing causes to the formation of those 

 original and suggestive ideas which were the foundation 

 of his greatness. 



Upon returning home in 1836 Darwin began to look 

 for facts in relation to the origin of species, upon which 

 he had reflected long before. A year later, after reading 

 Malthus's Essay on the Principle of Population, it 

 occurred to him that in the struggle for existence among 

 animals and plants, individuals which possessed varia- 

 tions favourable to particular circumstances would tend 

 to be preserved, while those having unfavourable 

 variations would be destroyed. The result would be 

 the formation of a new species. Darwin fully understood 

 the possibility of new species being produced by 

 " sports " or " discontinuous variations," but he showed 



