12 HISTORY OF THE HUMAN BODY 



The adaptations of the soma are extremely gradual, and 

 thus, if all forms that have ever existed could be arranged in 

 order, they would form a continuous series, not in the form of 

 a straight line, but in that of a profusely branching tree, since 

 from one parent form two or more varieties are constantly 

 arising, capable of inhabiting a slightly different environment, 

 and, if successful, continuing along separate lines of develop- 

 ment. As a matter of fact, however, the fauna and flora of 

 the world at present represent, for the most part, but isolated 

 units in the great system, and while a careful study of the 

 structure of every known form has led to the restoration of 

 many portions of this tree, there are in other places great gaps 

 filled thus far only by inferences, and therefore matters of 

 continual controversy. 



v This continuity of all life and the recognition of animals 

 and plants as no more than the countless adaptive forms of 

 the plastic soma, enable the zoologist to trace out with con- 

 siderable accuracy the history of those series of which the 

 records are the best preserved, a history which, while lying in 

 the past, is represented in the present by forms which arose in 

 earlier periods, the complete adaptation of which has allowed 

 them to successfully struggle with their competitors and thus 

 to survive with but little change to the present day. It is in 

 this sense, then, that there can be a history of the human body, 

 the history of the struggles and successes and" failures of our 

 remote ancestors, as they successively encountered the various 

 environments wherein this history has been enacted. The 

 ocean, the marsh, the prairie, the forest, each has formed the 

 complex stage-setting of an historic period and has contributed 

 to the formation of the human soma. Man's body was, like all 

 others, not made new, but adapted, and this not once, but 

 repeatedly. Old organs have been readapted to new uses or 

 are retained as merely functionless rudiments, new organs have 

 arisen through the change of function of some preexisting 

 part, the body has in all its details been molded and shaped 

 with each new change to the end of producing the highest 

 degree of physiological efficiency, and this always with sole 



