ASPECTS OF KINETIC EVOLUTION 2$l 



lutionary progress in mechanical effects of environmental influ- 

 ences. A large number of special phenomena of artism have 

 been named, such as heliotropism, or the power of plants to grow 

 toward the light or to turn themselves to face the sun. Ge- 

 otopism is the opposite tendency of the roots to bury themselves 

 in the soil. 



Some writers on " evolutionary mechanics" have gone so far 

 as to name the tendency of birds to stand or fly facing the wind 

 as pneumotropism, and of fish to head up stream as rheo- 

 tropism. Consistent prosecution of this tendency to ascribe 

 special " forces," and to give technical names to each habit or 

 instinctive act could result only in confusion, worse, indeed, than 

 the older practice of ascribing all unexplained organic phe- 

 nomena to a general "vital force." Even the operations of 

 agriculture are conducted by many primitive peoples on an in- 

 stinctive rather than a rational basis. In spite of permanent 

 employment and a fully assured supply of food, the Indians of 

 Central America obey an internal compulsion to scatter upon 

 the land, when the proper season comes, to clear and plant their 

 corn fields. Owners of mines and plantations have reconciled 

 themselves to a complete suspension of work during the corn- 

 planting weeks, having learned by experience that it is useless 

 to oppose or to reason with this irresistible agricultural impulse. 



It would be possible, of course, to describe this agricultural 

 instinct as a form of geotropism, a turning to the land for food 

 as the root turns to the soil. The practical point is not, how- 

 ever, the choice or application of terms, but to note the prob- 

 ability that the instinctive actions by which man and the higher 

 animals adapt themselves to environmental needs belong to the 

 same general class of phenomena as the accommodative changes 

 of plants. We know why we clear the land and plant our crops, 

 and if the need or the advantage be not present we have no 

 difficulty in discontinuing our agricultural labors, but it is not 

 likely that agriculture arose, in the first place, as a conscious 

 and deliberate art. Its beginnings are probably to be traced 

 back by imperceptible stages to the primitive root crops of trop- 

 ical America which grow readily from cuttings of the stems and 

 rootstocks, so that the digging and harvesting of one crop plants 

 and cultivates the next. 



