404 CONCLUSION 



not. There is no bar to the appearance of characters 

 which are of no use to the organism, nor even of char- 

 acters which are disadvantageous to it, provided they 

 do not handicap the organism sufficiently to destroy its 

 chances of continued existence. 



Proof that a structural or functional character is of 

 use to an organism is no explanation of the origin of 

 the character in question. A useful character, even 

 when the organism could not survive without it, is 

 merely an expression of a partial equilibrium with the 

 environment. The origin, that is the causation of a 

 character, is not to be sought along these lines, but by 

 studying the play of forces at work. We have con- 

 sidered several cases, for instance the origin of the 

 sexual differentiation of algal gametes (pp. 200-202), 

 the causes 01 the differentiation between the external 

 and internal cells in the Brown Seaweeds (p. 228), the 

 ability of the fruits or seeds of many seashore and 

 riverside plants to float in water for a long time with- 

 out injury (p. 372), in which it is clear that the 

 causation of these characters is distinct from their 

 advantageousness to their possessors. Their usefulness 

 may explain their maintenance, but not their origin. 



All characters alike, essential, useful, useless, or 

 harmful, are the inevitable products of an organism's 

 constitution in the last analysis of the constitution of 

 its protoplasm reacting according to the laws of 

 physics and chemistry to the conditions of its environ- 

 ment. The science of biology, like every other science, 

 is concerned with causation, the fixed relations between 

 phenomena, and it is only by the study of the 

 causation of the characters of living organisms that 

 our knowledge of biology can be advanced. 



