340 THE CHANGING GENERATIONS 



"The Origin of Species." For 20 years more Darwin accumulated 

 data from all fields of biology, sifting and testing it, making new observa- 

 tions and experiments, and looking always for facts that might disprove 

 as well as support his hypotheses. Gradually he built up, on the one hand, 

 a vast body of facts that demonstrated beyond question that evolution 

 had occurred and, on the other, a theory of organic evolution that seemed 

 to fit the known facts. During nearly all this period of intensive work he 

 was in ill health and lived the life of an invalid and recluse. 



In 1857, he ventured to submit a draft of his theory to a number of 

 his scientific friends for comment and criticism. The following year, 

 he received a manuscript from Alfred Russel Wallace, a young naturalist 

 who was studying the distribution of life in the Malay archipelago. 

 Wallace, like Darwin, had been particularly impressed by the diversity 

 and the peculiarities of distribution of living things, and he, too, had 

 chanced to read Malthus. His conclusions, reached independently, were 

 much like those of Darwin but had not undergone the searching criticism 

 of 20 years' study. Wallace asked that, if the paper seemed of sufficient 

 merit, Darwin should present it to the Linnaean Society, not knowing 

 that the older man had been working along similar lines. Darwin might 

 have done this, suppressing his own work, had not his friends persuaded 

 him to make an abstract to present along with Wallace's paper at a 

 meeting of the Linnaean Society in July, 1858. The joint paper created a 

 tremendous turmoil — the first great debate on evolution. The following 

 year, in November, 1859, The Origin of Species was published. 



In many respects modern biology may be said to date from the appear- 

 ance of this work. Although some of the older biologists refused to accept 

 evolution, it rapidly became established as one of the basic principles of 

 biology — perhaps the most fundamental of all, since this single concept 

 affords a common explanation and correlating factor for the findings from 

 all fields of biological research. Its influence has been equally far-reaching 

 outside the field of biology and has profoundly affected all science and 

 philosophy. 



The proof of the fact of evolution. The Origin of Species really 

 did two things, though they were not treated by Darwin as distinct. 

 First and most important, it presented proof that evolution has actually 

 occurred. This proof consisted of thousands of laboriously accumulated 

 facts that are understandable only on the assumption that the species 

 of animals and plants are of common descent and have become different 

 from their ancestors. This conclusion is now unquestioned by biologists. 



The theory of natural selection. In the second place, The Origin of 

 Species offered Darwin's explanation of the mechanism of evolution. 

 In formulating this theory Darwin found his essential clues, first in 

 the effects of artificial selection of variations occurring among domestic 



