340 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



were deposited, as well as for hints as to probable land and sea con- 

 nections in the past. Biogeograpliical studies, then, interlocked as 

 they are with geology and paleontology, contribute to two different 

 fields, primarily to a knowledge of how living things evolved and 

 migrated and secondarily to a better imderstanding of the changes 

 of land and sea areas and of climate during geological time. 



For many reasons, biogeographical problems are often difficult to 

 solve, although some workers have been slow to realize this difficulty. 

 The classical distributional researches of Darwin, Wallace, and their 

 contemporaries tlirew a bright light on subjects that had been little 

 thought about, and many of their followers lost sight of the fact that 

 the most brilliant of the first results were drawn from those instances in 

 which plain evidence was lying fallow to produce richly for those first 

 in the field. Year by year the literature of biogeography grows, and 

 as vast new stores of precise facts pile up, problems that formerly 

 seemed simple become increasingly difficult to solve. Indeed, it is 

 apparent that the data of the science are already too vast for any 

 single person to digest, even in relatively circumscribed problems. 

 Most biogeographers of today are of necessity narrower specialists 

 than their predecessors; each has a large and growing body of fact 

 in his own specialty to master and less time to acquire the geological 

 background and knowledge of the hterature of other fields that would 

 enable him to see distributional problems in true perspective. It 

 would seem that general biogeographical results of lasting value can 

 be reached nowadays only through the cooperation of a group of 

 competent specialists who can weigh apparently contradictory evi- 

 dence and reach conclusions in accord vsdth the soundest bodies of 

 biological, ecological, paleontological, and geological fact. 



ZOOGEOGRAPHICAL PROBLEMS OF THE AMERICAS 



Biogeographical problems are legion, ranging from questions of con- 

 tinental and oceanic relationships to minute details of the distribu- 

 tion of single species, but at this time I wish to speak only of a very 

 few of the broader problems of the animal geography of North and 

 South America. 



Generally spealdng, zoogeographers, hke Gaul, are divided into 

 three parts — those who build bridges, those who do not, and the pro- 

 ponents of continental drift. To begin with the last first, it may be 

 explained that Wegener and his followers believe that all the conti- 

 nents once formed a more or less compact land mass floating upon the 

 deeper, heavier rocks of the earth's crust, and that sundry pieces of 

 this land mass broke off from time to time and drifted away to form 

 what we now call Australia, the Americas, and Africa. Despite the 

 fulminations of those opposed to this theory, there is a considerable 

 body of weighty evidence in favor of it, and I for one, should not be 



