778 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



subsequent distributional studies by students or disciples of Matthew have been 

 based on Matthewsian principles; and the modern period in zoogeography must 

 be dated from 1915. Matthew demonstrated that no hypotheses of trans-Pacific 

 or trans- Atlantic connections between the continents are required to explain the 

 existing distributions of mammals, and that the Mesozoic and Tertiary bridges 

 between Asia and North America at Bering Strait and over the shallow Bering 

 Sea, the Isthmus of Panama, with the perhaps still earlier bridge via the 

 unstable island area between Australia and southeastern Asia, are the only con- 

 tinental connections for which valid evidence exists. This is documented from 

 Matthew's unparalleled knowledge of mammalian paleontological history. As 

 Darwin and Wallace and Handlirsch had rightly remarked, the axiom of general 

 stability of the continents (to the outlines of the continental shelves) is essential 

 to any orderly and critical investigation of animal distribution. Matthew could 

 rest renewed affirmation of this axiom on the geological evidence for isostasy. 



The more important contribution of Climate and Evolution is the presenta- 

 tion of an outline on the world scale, and in the grandest historical perspective, 

 of the dispersal of land animals throughout geological history. This rests on the 

 synthesis by Chamberlin and Moulton of the evidence from geological history as 

 a whole for periodic cycles of great uplift of the continents with corresponding 

 climatic extremes, diversity, and change, alternating with base-leveling by erosion 

 ending in widespread uniformity and amelioration of climate. Matthew suggests 

 that these large-scale changes have dominated progressive and adaptive evolution, 

 and that ancestral types that failed to enter the main currents of evolution have 

 either followed the climatic changes in their dispersal, to avoid the necessity 

 of change, or have been forced by the competition of the advancing and physio- 

 logically more progressive types into geographically peripheral regions. 



The examination of existing and fossil types at the peripheries of the ranges 

 of their groups documents this broad pattern of dispersal. The continents of the 

 southern hemisphere extend like vast peninsulas from the larger land masses of 

 the northern hemisphere. It is demonstrable from the paleontological record that 

 these larger northern land masses have been the main theaters of the evolution 

 of mammals; and the southern continents are veritable museums of relict types 

 preserved from past ages, whose ancestors are often known to have been present 

 at earlier times in the northern hemisphere. Centers of origin are to be expected 

 where the more advanced forms now live rather than where the most primitive 

 forms are found. 



Recognizing that the evidence from paleontology becomes progressively more 

 obscure from the well-documented Tertiary history of the Age of Mammals 

 through the Age of Reptiles in the Mesozoic to the origins of land animals in the 

 Paleozoic, Matthew pleads for the interpretation of the less known by means 

 of the better known, and doubts the existence of transoceanic connections of the 

 southern continents even in the more remote geological periods. This is essen- 

 tially the application of the "law of parsimony," which is basic to critical scien- 

 tific thought. 



The absurdity of Arldt's determination of the probability of past trans- 

 Atlantic and trans-Pacific land connections by means of a statistical analysis 

 of the "votes" of zoologists becomes evident after a critical examination of 

 Climate and Evolution. This work disposes of the supposed necessity for such 



