184 I)i/ii<n>iie TJieory. 



to the protophyte alga of Laurentian days. Plants now live largely pn 

 the remains of their dead ancestors, and finding so much work done by 

 those ancestors in subduing the mineral soil of the earth and impregnat- 

 ing it with organized materials more easy of assimilation by the tissues of 

 plants, those now living are endowed with a less vigorous and rugged 

 constitution, that is, have lost certain functions possessed by their 

 ancestors. Tn most cases they have gained .other functions of a higher 

 order than those lost, and with them a new and more complicated mor- 

 phology. This leads to the observation that while the organism strug- 

 gles directly with the rugged and incult forces of nature, its own devel- 

 opment must be limited and its functions must remain simple in corres- 

 pondence with the simplicity of the forces of the environment. But the 

 reactions of the organism change the conditions of the environment not 

 only by work done, but both in the case of plants and animals, but par- 

 ticularly plants, their own remains contribute to place the environment 

 under different conditions at the end of every generation, so that suc- 

 ceeding generations are by their means placed under new stimuli, and, 

 getting the benefit of the lives of those gone before, are able to attain a 

 different development. The roughest work having been done they do 

 not have it still to do. 



Such language as this must not mislead us into a conception of or- 

 ganisms doing something ; the real fact being that the forces of the en- 

 vironment having, by the creation and destruction of a generation of 

 organisms and the addition of their reactions, and the reaction of their 

 remains to the environment, changed it by so much, these forces are en- 

 abled to produce a new generation different from the first, and having 

 functions fitted for a new state of things. As a bricklayer may lay an 

 upper course only after he has laid a lower one. 



The very same principles govern the action of contemporaneous or- 

 ganisms upon one another. A certain organism requires to have cer- 

 tain work done for it. If this essential work can be done by another 

 organism ( or, rather, through it ), organism number one may rest from 

 that labor or may do something else, but if he does, his ability to per- 

 form that labor will be diminished. He may acquire some other ability 

 in its place, or in some way render an equivalent or partial compensa- 

 tion for the work thus done for him. Thus man puts upon a horse a 

 great deal of work he would otherwise have to do himself, but he re- 

 turns some of his own work in furnishing the horse a sheltered stall and 

 a secure supply of food. Man's relations with his domestic animals are 

 akin to a mutual parasitism with the inevitable effects of parasitism in 

 reducing some of the personal functions. Our ape-like ancestors were 

 endowed with a hairy covering which, no doubt, sufficed to preserve a 

 sufficient warmth for ordinary comfort. But a luxurious habit of sup- 



