No. 643] 



ORTHOGENESIS 



selves are not sufficient to establish the validity of any 

 theory of the mechanism of evolutionary variation. 



II 



More important than speculating about such questions 

 is the fact that the underlying physico-chemical processes 

 in living organisms seem to have remained about the 

 same throughout the whole process of evolution. So far 

 as it is possible to form any opinion on the matter, this 

 conclusion is inevitable. 



In considering the question of organic evolution it 

 should always be remembered that, with very trivial ex- 

 ceptions, the economy of life on the earth is now and prob- 

 ably always has been founded upon the synthesis of car- 

 bohydrates from water and carbonic acid with the ac- 

 companying fixation of energy, followed by the conver- 

 sion of carbohydrates into fats, proteins, and a great 

 variety of other related substances. Later there is an 

 oxidation of these substances back to water and carbon 

 dioxide, accompanied by the utilization of the eiiorgy in 

 various forms of organic activit.\-. Corrt'latid witli this is 

 the fact that cells are made up of watd-. (•ail)()ni(' acid, 

 carbohydrates, fats, proteins, and certain other sub- 

 stances. They are enough alike in chemical composition 

 and in physico-chemical structure fully to justify the 

 concept of protoplasm as a fairly constant physico-chem- 

 ical apparatus throughout the organic world. 



These familiar facts of chemical physiology and chem- 

 ical morphology undoubtedly depend upon the properties 

 of the substances involved. Water and carbonic acid, 

 witli which the process begins and ends, and which seem 

 to l)e everywhere the foundation of protoplasm, possess 

 in themselves such a large number of remarkable char- 

 acteristics and lead directly through the formation of 

 sugars to such a u^vat vari.'ty o\' clieniica] snbstaiic(>s and 

 chemical reaction-, tliat it is hard to Ix'licve in tho ])os- 

 sibility of the existence on a large scale of any very dif- 

 ferent kinds of living organisms. 



