494 THE THEORY OF EVOLUTION 



certain facts of marine ecology that are suggestive of this interpre- 

 tation. 



These suggestions regarding the time, the manner, and the place 

 in which living beings had their origin on our planet are not solu- 

 tions of th^ problem; but in science we must be content to face 

 such unsolved problems in the hope that a solution may be eventu- 

 ally obtained. The question lies in the field of biological specula- 

 tion. Such speculations are profitable if based upon facts and not 

 too greatly extended. They appeal to the imagination and are 

 worth discussion if one does not neglect other problems that are 

 open to solution. 



Organic Evolution 



The History of Organisms. — We have seen that Inorganic Evo- 

 lution is the historic process of change by which the world of lifeless 

 objects has reached its existing state and by which it is changing 

 at the present time. A similar definition applies to Organic Evolu- 

 tion, which is the process by which existing animals and plants 

 have come to be what they are in the course of their descent from 

 ancestral forms of a different nature. The word "development" 

 has been used for the changes by which the many-celled organism 

 arises from the egg. One may, however, speak of " evolutionary 

 development " as well as the development of the individual. • 

 Organic Evolution, or Evolutionary Development, is, therefore, 

 the history of living things as interpreted by the biologist. As 

 with the facts and interpretations of Geologic Evolution, the con- 

 clusions regarding Organic Evolution are based upon evidence 

 that is immediately before us, such as the structure and develop- 

 ment of animals, their distribution over the earth, and the fossils 

 in the rocks. 



The Fact, Course, and Cause of Organic Evolution. — Much 

 confusion arises regarding Organic Evolution through failure to 

 distinguish between what may be termed the fact, the course, and 

 the cause in such a progressive series of events. This may be illus- 

 trated by an analogy. Let us suppose that a ship leaves a Euro- 

 pean port and sails across the Atlantic to New York. One may 

 distinguish between the fact that the ship crossed the ocean, 

 instead of being created in New York Harbor; the course it pur- 

 sued, whether a northern or a southern route; and the causes that 

 made the ship go, whether internal forces like steam and elec- 



