56 THE FOUNDATIONS OF SCIENCE 



credited further by the scientific doctrine of fixity of 

 species prevalent in the eighteenth and early nine- 

 teenth centuries. 



Lamarck (1744-1829), it is true, had advocated a 

 theory of evolution founded on the idea of the gradual 

 development of organs under the stimulus of special 

 use for many generations the giraffe, for instance, 

 acquiring its long neck by the continual efforts of 

 its ancestors to browse on trees just beyond their 

 reach. But no evidence was forthcoming of the 

 inheritance of such acquired characters, and the 

 balance of scientific opinion was decidedly against 

 the evolutionary hypothesis. 



In 1858, however, a new suggestion was made 

 independently by Charles Darwin (1809-1882) and 

 Alfred Russel Wallace (b. 1823), fortified in the 

 case of Darwin by illustrations drawn from many 

 years' observation and experiment. Impressed by 

 the severity of the struggle for life and for mates 

 among animals and plants in a state of nature, 

 Darwin and Wallace saw that a variation in struc- 

 ture or character which gave even a slight advantage 

 to any individual might determine the question 

 whether or not it was to survive, obtain a mate, 

 and rear offspring. Innate variations tend to be 

 inherited, and thus a favourable variation might be 

 perpetuated, developing in time into a new variety or 

 species. In this way, the pressure of natural selec- 

 tion might accentuate chance variations, and produce 



