370 THE EVIDENCE OF EVOLUTION. 



name for the sudden and accidental changes of species into one 

 another was regularly used. At that time they were called 'mu- 

 tations', and the phenomenon of mutability was more or less clearly 

 distinguished from that of variability in a more limited sense. Espe- 

 cially in France a serious scientific conflict raged on this point about 

 the middle of the last century, and its near relation to religious 

 questions secured it a large interest. Jordan and Godron were the 

 leaders and numerous distinguished botanists and zoologists enrolled 

 themselves under their banners. They cleared part of the way for 

 Darwin and collected a large amount of valuable evidence. Their 

 facts pleaded for the sharp and abrupt delimitation of their species, 

 and asked for another explanation than that which was derived 

 from the ordinary, slow and continuous variations. 



Their evidence, however, was not complete enough to command 

 the decision in their behalf. The direct proof of the sudden changes 

 could not be offered by them, and they allowed themselves to be 

 driven to the acceptance of supernatural causes on this account. 

 Thereby, however, they lost their influence upon the progress of 

 science, and soon fell into oblivion. 



Instead of following this historical line, however, I have now to 

 point out one of the weightiest objections against the conception 

 of the origin of species by means of slow and gradual changes. It 

 is an objection which has been brought forward against Darwin 

 from the very beginning, which has never relented, and which often 

 has threatened to impair the whole theory of descent. It is the 

 incompatibility of the results concerning the age of life on this 

 earth, as propounded by physicists and astronomers, with the de- 

 mand made by the theory of descent. 



The deductions made by Lord Kelvin and others from the central 

 heat of the earth, from the rate of the production of the calcareous 

 deposits, from the increase of the amount of salt in the water of the 

 seas, and from various other sources, indicate an age for the inha- 

 bitable surface of the earth of some millions of years only. The 

 most probable estimates lie between twenty and forty millions of 

 years. The evolutionists of the gradual line, however, had supposed 

 many thousands of millions of years to be the smallest amount that 

 would account for the whole range of evolution, from the very first 

 beginning until the appearance of mankind. 



This large discrepancy has always been a source of doubt and a 

 weapon in the hands of the opponents of the evolutionary idea, and 

 it is especially in this country that much good work has been done 



