598 GENETICS AND EVOLUTION 



the germ cells (germ plasm), and only traits present in the germ plasm 

 are transmitted to the next generation. 



297. Background for The Origin of Species 



Charles Darwin made two great contributions to the body of scien- 

 tific knowledge: he presented a wealth of detailed evidence and cogent 

 arguments to show that organic evolution had occurred, and he formu- 

 lated a theory, that of natural selection, to explain the mechanism of 

 evolution. 



Darwin was born in 1809 and was sent at the age of 15 to study 

 medicine at the University of Edinburgh. Finding the lectures intoler- 

 ably dull, he transferred, after two years, to Christ's College, Cambridge 

 University, to study theology. Many of Darwin's friends at Edinburgh 

 were interested in geology and zoology, and at Cambridge he joined a 

 circle of friends interested in collecting beetles. Through them he came 

 to know Professor Henslow, the naturalist. Shortly after leaving college, 

 and upon the recommendation of Professor Henslow, Darwin was ap- 

 pointed naturalist on the ship Beagle, which was to make a five-year 

 cruise around the world preparing navigation charts for the British 

 Navy. The Beagle left Plymouth in 1831 and cruised slowly down the 

 east coast and up the west coast of South America. While the rest of 

 the company mapped the coasts and harbors, Darwin studied the ani- 

 mals, plants and geologic formations of both coastal and inland regions. 

 He made extensive collections of specimens and copious notes of his 

 observations. The Beagle then spent some time at the Galapagos Islands, 

 west of Ecuador, where Darwin continued his observations of the flora 

 and fauna, comparing them to those on the South American mainland. 

 These observations convinced Darwin that the theory of special creation 

 was inadequate and set him to thinking about alternate explanations. 



Upon his return to England in 1836, Darwin spent his time assem- 

 bling the notes of his observations for publication and searching for 

 some reasonable explanation for the diversity of organisms and the 

 peculiarities of their distribution. As Darwin wrote in his notebook: 



"On my return home in the autumn of 1836 I immediately began to prepare my 

 journal for publication, and then saw how many facts indicated the common descent of 

 species. ... In July (1837) I opened my first notebook for facts in relation to the origin 

 of species, about which I had long reflected, and never ceased working for the next twenty 

 years. . . . Had been greatly struck from about the month of March on character of South 

 American fossils, and species on Galapagos Archipelago. These facts (especially latter) 

 origin of all my views. . . . 



"In October (1838), that is fifteen months after I had begun my systematic inquiry, I 

 happened to read for amusement Maltlius on Population, and being well prepared to 

 appreciate the struggle for existence which everywhere goes on, from long-continued 

 observation of the habits of animals and plants, it at once struck me that under these 

 circumstances favorable variations would tend to be preserved, and unfavorable ones to 

 be destroyed. The result of this would be the origin of new species. Here then I had at 

 last got a theory by which to work." 



Darwin spent the next twenty years accimiulating data from many 

 fields of biology, examining it critically, and building up a tremendous 



