Chap. 38 ORGANIC evolution — conservation 791 



Back in England, in London for a time, and later living in nearby Down, 

 he pondered upon the plants and animals that grew crowded together. He also 

 read the essay in which Malthus told of the human populations that became 

 too large for the space available to them (1838). This suggested a plan. Some 

 organisms must be winnowed out by their natural surroundings; thus, others 

 would be benefited. There would be a natural selection. 



In 1844, Darwin wrote a summary of his theory but continued to gather 

 facts from his own observations and those of others. In the meanwhile, Alfred 

 R. Wallace (1823-1913), another English naturalist, arrived independently 

 at conclusions similar to those of Darwin. He had reached his conclusion also 

 after an exploring trip through the tropics. By mutual agreement and especially 

 through the desire of Darwin, the respective views of Darwin and Wallace were 

 read to the Linnaean Society, in London, on June 30th, 1858. Wallace shared 

 with Darwin the credit of propounding the theory of natural selection and 

 there was sincere friendliness between the two naturalists. Now, Darwin has 

 become famous throughout the world for a theory supported by thousands of 

 observations and years of study. And now, Wallace is relatively little known 

 for a conclusion which he arrived at honestly, independently and quickly, but 

 with little critical treatment and relatively few examples for proof. 



Changes Preserved by Selection. The Origin of Species by Natural Selection, 

 or the Preservation of Favoured Races in the Struggle of Life, by Charles Dar- 

 win was published in 1859. It is regarded as the most widely influential book 

 of the nineteenth century and the leading classic in biology. Its effect upon 

 sciences and society in general was due to the vital nature of the theory and 

 no less to the convincing presentation of facts supporting it. The following 

 summary contains the essence of the theory. 



1. Variations occur in individuals and species. 



2. The numbers of every species tend to become enormously large, yet the 

 population of each remains nearly constant because of the effects of climate, 

 competition of other organisms, and other factors that eliminate many indi- 

 viduals. 



3. This involves a struggle for existence. During this struggle, individuals 

 in which variations are favorable continue to live and produce their kind 

 whereas those having variations that are unsuitable in nature are eliminated. 



4. A process of selection by the environment or natural selection operates. 



5. There is a natural preservation of those that fit into a certain niche in 

 nature, a survival of the fittest. 



Within a year after "The Origin of Species" was published Darwin admitted 

 that it would have been better to use "natural preservation" as a key phrase 

 for the theory. 



The majority of biologists accept Darwin's theory as the most adequate 

 statement of evolution. Disagreements with it have been based upon the better 



