CHAPTER III 



USE AND DISUSE 



Kegeneration Adaptive acquirements The co-ordination of animal 

 parts The effects of use and disuse The evolution of the power of 

 making adaptive acquirements. 



49. IT is admitted very generally by the followers of the 

 Lamarckian doctrine that Natural Selection must have 

 played a great part in the evolution of living beings, 

 especially in the evolution of plants and the lower races of 

 animals ; but they insist strongly that many characters, 

 particularly in the higher races of animals, are such that 

 they can have arisen only through the inheritance of the 

 effects of use and disuse. It is well, therefore, to test 

 the Lamarckian doctrine of heredity by the known facts of 

 evolution. The test is a decisive one. 



50. When multicellular organisms were first evolved 

 from unicellular types, it is extremely probable that all the 

 cells constituting the mass were similar in form and function ; 

 and that, therefore, like the ancestral unicellular organism, 

 every cell was capable of performing all the functions of 

 life, namely, nutrition, reproduction, locomotion, and the like. 

 Later, presumably as a result of Natural Selection, differenti- 

 ations gradually appeared among the adherent cells of the 

 community, some taking on, more and more, one special 

 function, and some another, till at length a high degree of 

 differentiation resulted. Reproduction of the race was then 

 delegated to the germ-cells, while all the other cells also 

 devoted themselves to particular functions. 



51. Among unicellular organisms every cell is a germ-cell, 

 and as such is capable of continuing the race. Among low 

 multicellular types the power persists in many cells, and the 

 environment decides whether it shall be exercised or not ; 

 thus, if almost any fragment of a sponge be bedded out, it will 



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