228 ORGANIC EVOLUTION CONSIDERED 



As a supply of food for winter, they store up a 

 large number of logs under the water, the bark of 

 which they consume. 



In this case we find an organized community work- 

 ing for the common good in constructing the dam 

 and the ditch and storing up food, and then making 

 special preparation for living in small groups by con- 

 structing their lodges and connecting them with the 

 ditch. 



Here we see highly-developed instincts that look to 

 the future good of the organism. The building of the 

 dam, the digging of the ditch, the storing of the 

 food are all done to meet future emergencies. 



It is evident that the construction of a dam could 

 not have been evolved gradually, for a dam must be 

 of sufficient extent to be useful before natural selec- 

 tion could act. 



Are we to presume that beavers experimented for 

 countless generations, thereby building up the instinct 

 which leads them to construct a dam? If so, on what 

 ground can we explain the preservation of the incip- 

 ient instinct until it was sufficiently developed to be 

 of practical use? In what way could they have known 

 in advance, or had an instinct in advance, that a dam 

 would serve their good? Shall we assume that their 

 instinct in the first instance led them to construct a 

 dam, they not having had any experience to evolve an 

 instinct of this kind? If the instinct existed without 

 having been evolved by experience, then we cannot 

 account for its evolution. If evolved, then we must 

 assume that the first dam made was of sufficient use 

 to give its makers an advantage in the struggle for 

 existence, and that the instinct which caused its con- 

 struction was transmitted to their offspring. 



In accounting for the evolution of this instinct, as 

 in other cases, we necessarily begin with an instinct 



