THE EVIDENCE OF EVOLUTION. 393 



evolution is concerned. Now, if they can not be explained by the 

 sloAv and gradual accumulation of indiviihial variations, evidently 

 the second alternative of Darwin's orii-inal proposition remains. 

 This Avas based on the sports, on those rare and sudden changes Avhich 

 from time to time are seen to occur among cultivated plants, and 

 which in these cases give rise to new strains. If such strains can be 

 proved to offer a better analogy to real systematic species, and if the 

 sudden changes can be shown to occur in nature as well as they are 

 known to occur in the culti\ated condition, then in truth Darwinism 

 can afi'ord to lose the individual variations as a basis. Then there 

 will be two vast dominions of variability, sharply limited and 

 sharply contrasted with one another. One of them will be ruled by 

 Quetelet's law of probability and by the unavoidable and continuous 

 occurrence of reversions. It will reign supreme in the sciences of 

 anthroi)ology and sociolog}^ Outside of these, the other will become 

 a new'donuiin of investigation, and will ask to be designated by a new 

 name. Fortunately, however, a real new designation is not required, 

 since previous to Darwin's writings the same questions were largely 

 discussed and since in these discussions a distinct name for the sud- 

 den and accidental changes of species into one another was regularly 

 used. At that time they were called " mutations," and the phenome- 

 non of mutability was more or less clearly distinguished from that of 

 variability in a more limited sense. Especially 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 dis- 

 tinguished 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 

 exjilanation than that which was derived from the ordinary, slow, 

 and continuous variations. 



Their evidence, however, Avas not complete enough to command tlie 

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

 aould not he otiered 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 Aveightiest objections against the conception of 

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

 an objection which has been brought forAvard against Darwin from 

 the very beginning, Avhich has never relented, and Avhich often has 

 threatened to impair the Avhole theory of descent. It is the incompat- 

 ibilitj' of the results concerning the age of life on this earth, as pro- 



