Chapter I 



INTRODUCTORY 



I 



DARWIN'S THEORY 



THIS chapter deals with elementary facts that are familiar to 

 every biologist, and is intended for the general reader, to 

 whom, it is hoped, it may be of service. 



Evolution and Darwinism are not synonymous terms. Darwin 

 gave his theory to the world in 1859 > l n before this, Lamarck 

 had propounded a theory of evolution, i.e., an unfolding of the 

 higher forms of life, animal and vegetable, from the simpler. 

 According to Lamarck, all species have become what they are 

 through the moulding influence of external conditions (such as 

 food, climate, etc.) and of exercise : from these two sources arise 

 all variations, and characteristics thus acquired are handed down 

 to succeeding generations. This was not accepted by men of 

 science. Darwin's work was, not to originate the idea of evolu- 

 tion, but to show by what means it had been brought about. 

 This means he called the struggle for existence, to the action 

 of which was due an unceasing natural selection. The proposi- 

 tion which he set himself to work out is as follows : 



(1) The offspring of all organisms, whether animal or veget- 

 able, tend to resemble their parents. 



(2) The young are never exactly like their parents, but there 

 is always some variation. The variations are mainly " spontane- 

 ous " (by which term he meant that we cannot discover the cause 

 of them), and, to a less extent, due to the manner of life of the 

 parents and the environment in which they live, characteristics 

 thus acquired being handed down to the next generation. 



