THE LIVING MACHINE BUILDING FACTORS. 169 



sented in the germ plasm, and consequently it 

 would be inherited by the next generation. The 

 short-necked individuals being largely destroyed 

 in this struggle for food, it would follow that the 

 next generation would be a little better off than 

 the last, since all would inherit this tendency to- 

 ward a long neck. A few generations would then 

 see the disappearance of all individuals which did 

 not show either this or some other corresponding 

 advantage, and in this way the lengthened neck 

 would be added permanently as a part of the ma- 

 chine. When this time came this peculiarity 

 would no longer give its possessors any advan- 

 tage over its rivals, since all would possess it. 

 Now, therefore, some new variation would in the 

 same way determine which animals should live 

 and which should die in the struggle, and in time 

 a new modification would be added to the ma- 

 chine. And thus this process continues, one 

 variation after another being added, until the 

 machine is slowly built into a more and more 

 complicated structure, always active but with a 

 constantly increasing efficiency. The construc- 

 tion is a natural one. A mixing of germ plasm in 

 sexual reproduction or some other agencies pro- 

 duce congenital variations ; natural selection act- 

 ing upon the numerous progeny selects the best 

 of the new variations, and heredity preserves and 

 hands them down to posterity. 



All students of whatever school recognize the 

 force of this principle and look upon natural se- 

 lection as an efficient agency in machine build- 

 ing. It is probably the most fundamental of 

 the external laws that have guided the process. 

 There are, however, certain other laws which 

 have played a more or less subordinate part. The 



