^56 The Earth 



Charles R. Darwin. De Vries built on 

 the work of Charles R. Darwin (1809- 

 1882), who had done his work almost 

 half a century before. Darwin lived at 

 a time when geologists had just begun 

 to find evidence that the earth and its 

 inhabitants had a long history of change. 

 It had been believed by most scientists 

 of earlier days that the earth had always 

 been inhabited by the kinds of living 

 things they saw about them. Darwin be- 

 lieved so too when he began to work. 

 He changed his mind as his work pro- 

 gressed. As a young man of twenty-two 

 he took a post as naturalist aboard the 

 "Beagle," a British vessel which was to 

 make a trip around the world. For five 

 years Darwin made observations, re- 

 corded them, and collected specimens. 

 He studied rock layers and the fossils in 

 them, the formation of coral islands, and 

 the places in which animals and plants 

 lived. He observed, recorded, and col- 

 lected specimens from the oceans, des- 

 erts, and jungles. He noticed many 

 puzzHng facts about animals and plants. 

 But gradually he was able to read some 

 meaning into these observations. By the 

 time he returned to England he thought 

 it probable that plants and animals had 

 changed throughout the ages. He 

 thought it likely that new types arose 

 from preceding types. 



But Darwin needed more evidence. 

 At the time when Darwin was studying 

 the problem, the great fossil beds had 

 not been exposed. Nothing was known 

 about chromosomes or genes; in fact 

 when Darwin returned from the voy- 

 age of the "Beagle," the cell theory was 

 not yet well known. The problem was a 

 difficult one for him to solve; but he 



ajid Its Inhabitants Change unit x 



continued to search for facts and more 

 facts. For another twenty years he kept 

 on collecting facts that would support 

 or disprove his theory of organic evo- 

 lution. The longer he studied, the more 

 facts he found to support the theory. As 

 he studied he formulated a theory to 

 explain how new species could be de- 

 rived from existing species. He called 

 this the theory of natural selection. Dur- 

 ing all this time he made no public men- 

 tion of his work. 



Darwin and Wallace. Before Darwin 

 was ready to publish his views, he re- 

 ceived a report from Alfred Russell 

 Wallace who had just finished studying 

 the animals in the East Indies. In this re- 

 port Wallace presented the very ideas 

 that Darwin had so long been turning 

 over in his mind but had not yet pub- 

 lished: first, that the different species of 

 plants and animals arise by evolution; 

 and second, that evolution takes place 

 by the particular method that Darwin 

 considered most probable — by the 

 method of "natural selection." 



With characteristic fairness and gen- 

 erosity, Darwin was at first inclined to 

 publish Wallace's report and say noth- 

 ing about his ow^n conclusions. But 

 friends insisted that, since he had been 

 working on the problem for twenty 

 years, both he and Wallace should pre- 

 sent their reports at the same time. Dar- 

 win's generosity Mas matched by the 

 fine spirit of Wallace, who always gave 

 Darwin credit for having been the first 

 to develop the idea of evolution and for 

 having studied the problem more thor- 

 oughly. Darwin is considered one of the 

 world's greatest scientists. Why? See 

 Exercise 3. 



