290 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



and nn(lerstandin<:s that, as all liistor}^ shows, will be mere scraps 

 of paper, but from the intensive application to them of the very 

 science which has evolved them. 



Although the geological record is, and possibly will always remain, 

 incomplete, it has yet proved remarkably representative, and cer- 

 tain outstanding facts have been made out which are sufficient to 

 show that the lines of organic evolution as recorded in geology are 

 in accordance with what is theoretically probable, and with those 

 taken by the evolution of domesticated organisms and by human arts 

 and inventions. 



1. There can be no doubt that the stages of organic evolution 

 are correlated with and were actuated by the stages in the inorganic 

 evolution of the earth itself. That climatic change was effective 

 in inducing migration, and thus in sharpening the struggle for 

 existence against both enemy organisms and changed physical en- 

 vironment; that extension and restriction of land and water areas 

 in some cases brought about keener and more varied competition, 

 change of habit or food, and in others the destruction of potential 

 enemies and the securing of the advantages of a fair field for the 

 survivors; and that activity of the earth-crust in such things as 

 deposition and mountain building provided conditions for the exist- 

 ence of an increased range of varieties and the conse([uent struggle 

 between them: If we are not allowed to say that this brought about 

 the survival of the fit, it at least caused the destruction of the unfit, 



2. It may be stated as a biological law that every locality becomes 

 " full " of life, forms arriving or evolving to take advantage of the 

 special facilities offered. In consequence, resistance to the incur- 

 sion of new forms, even if they are exceptionally equipped, is very 

 great, and it is only occasionally that such new forms can make 

 good their immigration. There are, of course, marked exceptions, 

 but these generally occur when degeneration or overgrowth in size 

 accompanied by neglect of means of defense have occurred, or when 

 an area has been for so long sheltered from the wider and more 

 general course of evolution that it has fallen seriously behindhand 

 in the race. 



The geological record giA-es indirect evidence of the same '' filling " 

 of areas in the past in the extraordinary slowness with which 

 advanced types that have eventually made great headway estab- 

 lished themselves after their introduction; the earliest fishes, rep- 

 tiles, and mammals are cases in point. Imperfect as the first mem- 

 bers of these groups undoubtedly were, they must, even shortly 

 after their introduction, have possessed considerable advantages 

 over the older and established forms with which they found them- 

 selves in competition. In size and strength they Avere doubtless 



