vii LAW AND PRINCIPLE 191 



which filled the four years 1848-52. Throughout his 

 whole career as a collector, Wallace had before him the 

 problem of evolution and the cause of the origin of new 

 species in animate nature. Before leaving for South 

 America, in 1848, he wrote : 



I begin to feel rather dissatisfied with a mere local collection ; 

 little is to be learnt from it. I should like to take some one 

 family to study thoroughly, principally with a view to the theory 

 of the origin of species. By that means I am strongly of opinion 

 that some definite results might be arrived at. Dr. A. R. Wallace. 



While at Sarawak, in 1855, Wallace was still pondering 

 over the problem, which was rarely absent from his 

 thoughts ; and in a paper written at that time he con- 

 cluded that every species which had come into existence 

 in Nature was closely related to a species which preceded 

 it. This pointed clearly to evolutionary development, 

 and suggested when and where new species would be 

 introduced ; but it did not indicate how they could be 

 brought into existence. After the publication of his 

 paper, Wallace was informed by his agent that several 

 naturalists had expressed regret that he was " theorising " 

 when what he was expected to do was to collect facts ; 

 nevertheless, he still continued to consider the reason 

 why one species becomes changed either slowly or 

 rapidly into another. Though the cause of the change 

 was unknown, the utilitarian mind considered it more 

 important to increase the size of a collection of birds 

 and insects of which Wallace himself had gathered 

 nearly nine thousand separate species than to discover 

 how the various distinct forms had originated. 



In February, 1858, during a period of intermittent 

 fever at Ternate, he was pondering over the problem 

 when the conclusions arrived at by Malthus as to the 

 factors affecting increase or decrease of population 



