Method of Origin of New Species and Structures 413 



poverty. Yet though his labors were seemingly without immedi- 

 ate fruit, they were of great service, nevertheless, in awakening 

 men's minds to the problems and possibilities of evolution, and 

 thereby making the way easier for Darwin. 



Lamarck's theory is founded on two factors, — the alterability 

 of individuals, and the hereditary transmission of the results 

 thereof. 



The Alterability of Individuals. — This is not theory, but fa- 

 miliar fact. Everybody knows that our own muscles, with their 

 associated blood vessels, nerves, and bones, can be improved in 

 size and strength by exercise, as can our minds, and other features 

 of our being; and likewise these can all degenerate through disuse. 

 And so it is throughout the animal kingdom. The process is well 

 understood: the use of the part serves as a stimulus which leads 

 the organism to throw more material and energy into those parts, 

 precisely in the manner which we have studied already in the 

 chapter on Irritability. In the same chapter we have seen also 

 how plants can alter their structure under stimulation. Thus 

 some kinds of plants can develop a thicker epidermis under the 

 stimulus of dry air; some trees can apparently build stronger 

 stems under stimulation of bending by the wind ; and indeed there 

 seems to be no limit to the directions and degrees in which plants 

 can respond structurally, and adjustively, to stimulation. The 

 structural alterations thus produced in individuals, are called 

 acquired characters. 



Transmission of Acquired Characters. — This is the crucial point 

 in the theory of Lamarck. He held that characters acquired 

 during the life of the individual, as described above, are 

 transmitted to their later offspring, which, therefore, exhibit 

 larger muscles, or finer minds, or thicker epidermis, or stronger 

 stems, than would have been the case had the parents not devel- 

 oped those features. Lamarck actually uses the illustration of 

 the blacksmith's arm, powerfully developed in the practice of his 

 trade; and he maintains that the later-born sons of the smith will 



