THE VITAL FABRIC OF DESCENT 32 1 



Reproductive cytological processes have advanced from the 

 brief fusions and prompt redivisions of simple and equal cells 

 to intricate combinations which may not require renewal for de- 

 cades and centuries. The Sequoias of California and Dracaenas 

 of the Canary Islands live as individual trees for thousands of 

 years, and some of our cultivated plants have been grown from 

 cuttings since the earliest dawn of primitive agriculture, behind 

 all human history and tradition/ 



Still other avenues of vital motion and achievement are to be 

 seen in the complexity of individuals, sexes and polymorphic 

 forms which the higher plants and animals often maintain in- 

 side the same species, and in the multitudinous reproductive de- 

 vices and instincts for weaving this diversity into the still more 

 intricate fabric of descent ; a social evolution, in short, which is 

 at once the basis and the prophecy of the still higher intellec- 

 tual and personal development of man himself. 



SUMMARY OF KINETIC INTERPRETATION. 



The causes of evolution are still unknown, but we have arrived 

 at the perception that evolution has a very practical physiolog- 

 ical function which explains the general fact of progressive 

 change. Organisms are under the necessity of motion ; it is 

 the only way that they can maintain their stability and continue 

 to exist. Instead of being moved by environmental causes from 

 a condition of normal constancy of characters, they are, by their 

 very constitution, wheeled against the environment, seeking new 

 avenues along which motion can be made. Nor are their im- 

 pulses toward diversity and evolutionary progress limited to the 

 environmental side. Species of common origin and inhabiting 

 the same region are found, very often, to have become different 

 in many ways, internal as well as external, which can have no 

 direct reference to the environment. 



Instead of having been built upon any general rules or prin- 

 ciples of nutrition or tissue-formation, we find in different natural 

 groups the utmost diversity in the solutions of the same bionomic 

 problems, each a testimony of the protean constructive powers 

 of life and of the futility of physiological generalizations based 

 on single species or a few related types. 



'The Food Plants of Ancient America, Smithsonian Report, 1903, 481-497. 



