CHAPTER XVII 



THE ORIGIN AND DEVELOPMENT OF ORGANISMS: 

 HEREDITY AND VARIATION 



THE ORIGIN OF THE LIVING MACHINE NOT EXPLAINED 



EVEN if it were possible to explain perfectly the working of 

 the organic machine by mechanical principles, this would not 

 explain life. As we have noticed in Chapter I, living organisms 

 come into existence to-day only as the result of reproduction 

 from previously existing organisms. Granting that animals 

 and plants have the power of reproduction, we have still to 

 ask how these complicated machines came into existence. 

 One of the most revolutionary eras of thought has arisen in 

 the last fifty years as the result of the attempt of biologists 

 to explain how the innumerable animals and plants have been 

 brought to their present condition of existence. 



Of the primal origin of life we have no knowledge, and it 

 must be admitted we have little hope of ever gaining any. 

 Nor have we much idea of the first living things that appeared 

 in the world. Probably they were of the lowest type, possibly 

 even simpler than unicellular forms. One thing seems certain: 

 the first living things must have been endowed with the prop- 

 erties of growth and reproduction; for without these powers 

 they would not have been alive. We know of nothing simpler 

 than cells possessing these powers, and we cannot therefore con- 

 ceive the beginning of life as anything simpler than a bit of 

 reproducing protoplasm. 



THE FORCES WHICH HAVE PRODUCED ORGANISMS 



It has been the aim of biology to show how the endless 

 series of complicated animals and plants, now found in the 

 world, have been produced from the simplest forms of life. 



325 



