CONTRIBUTION OF THE SCIENCES 289 



As evidencing a eontiniioiisly changing evolution series, the most extra- 

 ordinary record of all history is that included in the paleoutologic record 

 of life, running down through the whole story of geology, practically to 

 the earliest strata. 



Xot only do w^e find the character of the earlier stratified rocks indicat- 

 ing atmospheric and climatic conditions similar to those now obtaining 

 on the earth, but we find these rocks containing traces of living forms sucli 

 as now are fitted to these climatic conditions. Throughout the whole 

 stretch of the strictly geologic record, conditipns in temperature and 

 humidity evidently kept within the range permitting development of 

 living forms. The period in which life came to be on this earth is repre- 

 sented by a chapter now destroyed. 



The life record is, to be sure, fragmentary, but in many groups it is 

 ■extraordinarily full. Although there is much to be desired, out of the 

 long series of events, certain features in the evolutionary sequence are so 

 clear as to be unavoidable. AYe find this record showing: (1) that life 

 has been in almost continuous state of change. From top to bottom 

 of the geologic section, in no two great groups of strata do we find that 

 the assemblage of living forms represented are the same; (2) we knovV 

 the life of each stage to exhibit closer resemblance to that found in strata 

 immediately above and to that immediately below than to the life repre- 

 sentation of the more remote divisions, and (3) we note that the series 

 of forms with certain common characters, but differing in grade of 

 specialization, generally trend toward greater specialization from earlier 

 toward later time. The way in which the changes took place may not 

 always be evident, and the paleontologist may admit his ignorance of the 

 <:-ause, but the fact of more or less rapidly changing definitely specializing!- 

 series of presumably connected or related types seems reasonably clear. 

 The evidence, taken in its entirety, furnishes strong support for tlio 

 view that life of all these stages is related, that the life of each stage U 

 derived or modified from that of a preceding stage, and that the who1<' 

 series indicates the continuity of life from earliest to latest time. 



Unlike the sequence in purely geologic history, we have here continuity 

 tind continuous progress in a definite direction. We have, however, note 1 

 that there is probably close relation between the continuous fluctuations 

 of the progressing living world and the fluctuations of earth climate anil 

 <»arth crust. Movements of the crust producing change of topography 

 and variation in distril)ntion of land and water, taken with changes of 

 climate, must have had important influence in keeping the currents of 

 life moving. A dead eartli without crustal movement and with unifor-n 

 oliniate might have limited greatly the ])ossi))ility of biological evoliitio/). 



