154 POPULATIONS OF THE SEA 



distant treasures beyond. The cycle is a vicious one for, generally 

 speaking, large masses of data must still be assimilated, organized, 

 and correctly interpreted on regional or worldwide scales before 

 the essential principles can be confidently formulated or the 

 unique explanation deduced for any given set of local or temporary 

 conditions. This should not deter us, however, from formulating, 

 as best we can, such working principles as will give structure to 

 existing knowledge and direction to new research. 



General Limitations of Paleobiogeographic Evidence 



Paleobiogeography is no exception to the rule that all construc- 

 tions of the mind are beset by two groups of limiting factors, 

 human and objective. 



Because thought processes are complex and language is linear, 

 the mental image of one mind cannot be conveyed instantaneously 

 and unerringly to another except in some forms of mathematical 

 expression, which do not apply generally to the complexities of 

 the biosphere. An imperfect means of communication at best, 

 language may become perversely irrational in relation to facts or 

 concepts with which one is emotionally involved. Weak arguments 

 may then be bolstered with unwarrantedly strong statements, 

 and, by way of compensation, strong probabilities may be stated 

 with uncalled for reserve. This is the involvement paradox (Fig. 1) 

 manifestations of which include the dubious use of expressions 

 such as must be, doubtless, and obviously — warning flags that invite 

 both reader and writer to reconsideration of the evidence. The 

 more interpretive the subject the more prevalent the effects of the 

 involvement paradox, and the focal problem of paleobiogeography 

 (and paleomagnetism) is the highly interpretive subject of the 

 former arrangement and orientation of the earth. 



Objective factors affecting the application of paleobiologic 

 evidence to paleobiogeographic problems are both external and 

 internal, but all are expressed and controlled by the broad external 

 conditions of geographic range, habitat variation, and time. The 

 general effect of these conditioning factors on the applications of 

 the evidence is roughly indicated in Fig. 2, where paleobiogeog- 

 raphy stands, within the matrix of evolution, as the intermediate 



