458 AN INTRODUCTION TO ZOOLOGY 



Species " in 1859. This immortal work gave the first satisfying 

 and truly scientific account of the process of organic evolution, and 

 further tried to account for the manner in which it is brought about 

 in nature. The theory of Natural Selection, as it is called, was first 

 conceived by Darwin in 1838, but it was not until he had given the 

 matter twenty years' further thought that he published a paper 

 conjointly with Alfred Russel Wallace in the Transactions of the 

 Linnaean Society, and followed it a year later by his book. A. R. 

 Wallace was a younger biologist working in Melanesia, who quite 

 independently arrived at conclusions very similar to Darwin's. 

 This joint publication was the beginning of a life-long friendship 

 between these two great men. 



Charles Darwin was born, strangely enough, in 1809, the year of 

 the publication of " Philosophic Zoologique." In 1825, he went to 

 Edinburgh to study medicine ; he stayed about two years, and in 

 1828 went to Cambridge. He was appointed naturalist to the 

 Beagle in 1831, and went on a voyage round the world in her that 

 lasted till 1836. This voyage played a great part in shaping his 

 ideas, and he has left a charming account of it in " The Voyage of the 

 Beagle." In addition to writing " The Origin of Species," Darwin 

 did an enormous amount of biological work. ' ' The Origin of Species/' 

 or, to give it its full title, " The Origin of Species by means of Natural 

 Selection, or the Preservation of Favoured Races in the Struggle 

 for Life," is a book that has probably influenced human thought more 

 than any other, and certainly was the foundation stone of modern 

 biology. We must consider briefly its main points. 



The tripod upon which this theory rests are the three factors 

 Variation, Heredity, and the Struggle for Existence, and we must 

 glance briefly at the meaning of each of these. 



Variation. Variations are extremely well known in our domestic 

 animals and plants, for no matter how much the offspring may re- 

 semble the parents it is never precisely the same. The various 

 members of one family are not absolutely alike. By recognising 

 and taking advantage of these variations man has been able to 

 achieve much. Thus, probably all the various species of cabbage, 

 cauliflower, broccoli and Brussels sprouts, etc., are derived from the 

 one wild species Brassica oleracea. In the same way apples, of which 

 we now grow about 1000 varieties, come from the wild crab apple. 

 The standard examples in the animal kindgom are the various kinds 

 of pigeon (Columba livia), of dogs, cattle, etc. In all these cases the 

 result has been attained by selecting and breeding from the forms 

 with the desired characteristics. As it has been done intentionally 

 by man in gardens or breeding pens it has been termed " artificial 

 selection." A similar kind of variation is to be seen in all living ani- 



