30 THE EVOLUTION THEORY 



But Darwin would hardly have achieved what he did if he had 

 been compelled to secure for himself a professional position in order 

 to obtain bread and butter. Such great problems demand not only 

 the whole of a man's mental energy,, they monopolize his time. 

 Studies of detail may well be taken up in leisure hours, but big 

 problems absorb all the thoughts and must always be present to the 

 mind, lest the connexion between the many individual inquiries, 

 which make up the whole task, be lost sight of. Darwin had the 

 good fortune to be a free investigator, and to be able to retire, on 

 his return from his travels, to a small property at Down in Kent, 

 there to live for his family and his work. Here he followed up the 

 idea of evolution which he had already formulated, and it has always 

 seemed to me the most remarkable thing about him, that he was able 

 to keep in mind and work up the hundreds of isolated inquiries that 

 were eventually to be brought together to form the main fabric of 

 his theory. When one studies his many later writings, one cannot 

 but be surprised afresh by the number of different sets of facts he 

 collected at the same time, partly from others, partly from personal 

 observation, and continually also from his own experiments. He 

 made experiments on plants and on animals, and the number of 

 people with whom he carried on a scientific correspondence is simply 

 astounding. In this way he brought together, in the course of twenty 

 years, an extraordinarily rich material of facts, from the fullness of 

 which he was able later to write his book on The Origin of species. 

 Never before had a theory of evolution been so thoroughly nrepared 

 for, and it is undoubtedly to this that it owed a great part of its 

 success ; not to this alone, however, but still more, if not mainly, 

 to the fact that it presented a principle of interpretation that had 

 never before been thought of, but whose importance was apparent 

 as soon as attention was called to it — the principle of selection. 



Charles Darwin championed, in the main, the same fundamental 

 ideas as had been promulgated by his grandfather, Erasmus Darwin, 

 by Treviranus, and by Lamarck : species only seem to us immutable ; 

 in reality they can vary, and become transformed into other species, 

 and the living world of our day has arisen through such transforma- 

 tions, through a sublime process of evolution which began with the 

 lowest forms of life, but by degrees, in the course of unthinkably long- 

 ages, progressed to organisms more and more complex in structure, 

 more and more effective in function. 



It is interesting to note at what point Darwin first put in his 

 lever to attempt the solution of the problem of evolution. He started 

 from quite a different point from the investigators of the early part 



