THE VALUE OF L I F I^: 



ual has his definite period of Hfe, whether it Hvcs only 

 a few hours, hke the one-day fly or the infusorium, or, 

 Hke the Welhngtonia, the dragon-tree of Orotava, and 

 many other giant trees, hves for thousands of years. 

 Even the species, the collection of like individuals, is 

 just as transitory, and so are the orders and classes that 

 embrace numbers of species of animals and plants. Most 

 species are confined to a single period of the organic 

 history of the earth ; few species or genera pass un- 

 changed through several periods, and not a single one 

 has lived in all the periods. Phylogeny, taking its stand 

 on the facts of paleontology, teaches unequivocally that 

 every specific living form has only existed a longer or 

 shorter period in the course of the many (more than a 

 hundred) million years which make up the history' of 

 organic life. 



Every living being is an end to itself. On this point 

 all unprejudiced thinkers are agreed, whether, like the 

 teleologist, they believe in an entelechy or dominant as 

 regulator of the vital mechanism, or whether they explain 

 the origin of each special living form mechanically by 

 selection and epigenesis. The older anthropistic idea, 

 that animals and plants were created for man's use, and 

 that the relations of organisms to each other were 

 generally regulated by creative design, is no longer accept- 

 ed in scientific circles. But it is just as true of the species 

 as of the individual that it lives for itself, and looks 

 above all to self -maintenance. Its existence and "end" 

 are transitory. The progressive development of classes 

 and stems leads slowly but surely to the formation of 

 new species. Every special form of life — the individual 

 as well as the species — is therefore merely a biological 

 episode, a passing phenomenal form in the constant 

 change of life. Man is no exception. " Nothing is con- 

 stant but change," said the old maxim. 



The historical succession of species and classes is, both 



387 



