THE LIVING MACHINE BUILDING FACTORS. 175 



method of the action of certain well demonstrated, 

 fundamental factors. Whether by natural selection, 

 or by the inheritance of acquired characters pro- 

 duced by the environment, or whether by the effect 

 of isolation of groups of individuals, the machine 

 building has always been produced in the same 

 way. A machine, either through the direct influence 

 of the environment, or as a result of sexual combi- 

 nation of germ plasm, shows a variation from its 

 parents. This variation proves of value to its 

 possessor, who lives and transmits it permanently 

 to posterity. Thus step by step, one part is add- 

 ed to another, until the machine has grown into 

 the intricately adapted structure which we call the 

 animal or plant. This has been nature's method 

 of building machines, all based upon the three 

 properties possessed by the living cell repro- 

 duction, variation, and heredity. 



Summary of Nature's Power of Building Ma- 

 chines. Let us now notice the position we have 

 reached. Our problem in the present chapter has 

 been to find out whether nature possesses forces 

 adequate to explain the building of machines with 

 their parts accurately adapted to each other so as 

 to act harmoniously for certain ends. Astronomy 

 has shown that she has forces for the building of 

 worlds; geology, that she has forces for making 

 mountain and valley ; and chemistry, that she has 

 forces for building chemical compounds. But the 

 organism is neither a world, nor a mass of matter, 

 nor a chemical compound. It is a machine. Has 

 nature any forces for machine building ? We have 

 found that by the use of the three factors, repro- 

 duction, variation, and heredity, nature is able to 

 produce a machine of ever greater and greater 

 complexity, with the parts all adapted to each 



