392 THE EVIDENCE OF EVOLUTION. 



Quetelet's celebrated law of variability Avas published only some 

 years after the appearance of Darwin's Origin of Species. Variabil- 

 ity seemed until then to be free from laws, and nearly everything 

 could be ascribed to it or explained by it. But the renowned Belgian 

 scientist showed that it obeys laws exactly in the same way as the 

 remainder of the phenomena of nature. The law which rules it is the 

 law of probability, and according to this law the occurrence of varia- 

 tions, their frequency, and their degree of deviation can be calculated 

 and predicted with the same certainty as the chance of death, of mur- 

 ders, of fires, and of all those broad phenomena Avith which the 

 science of sociology and the practice of insurance are concerned. 



The calculations of probable variations based on this most impor- 

 tant law did not, however, respond to the demands of evolution. 

 Specific characters are usually sharply defined against one another. 

 They are new and separate units more often than diiferent degrees of 

 the same qualities. Only Avith such, hoAVCA^er, Quetelet's laAA" is con- 

 cerned. It explains the degrees, but not the origin, or ncAv peculiari- 

 ties. Moreover, the degrees of deviation are subject to re Aversion to 

 mediocrity, always more or less returning in the progeny to the pre- 

 vious state. Species, on the contrary, are usually constant and do not 

 commonly or readily rcA^ert into one another. It is assumed that from 

 time to time specific reversions occur, but they are too rare to be com- 

 parable Avith the phenomena Avhich are ruled by the laAA' of probability. 



A thorough study of Quetelet's hiAv AA'ould no doubt at once liaA^e 

 rcA^ealed the Aveak point in DarAA'in's conception of the process of evo- 

 lution. But it Avas published as part of a larger inquiry in the 

 department of anthropology, and for years and A'ears it has been 

 prominent in that science, without, hoAA^ever, being applied to the cor- 

 responding phenomena of the life of animals and of plants. Only of 

 late has it freed itself from its bounds, transgressed the old narroAv 

 limits, and displayed its prominent and universal importance as one of 

 the fundamental hiAvs of liAdng nature. 



In doing so, hoAvcA^er, it has become the starting point for a critical 

 revicAv of the very basis of DarAA^n's conception of the part played by 

 natural selection. It at once became clear that the phenomena Avhicli 

 are rided by this hiAv, and AAdiich are bound to such narroAV limits, can 

 not be a basis for the explanation of the origin of the species. It rules 

 quantities and degrees of qualities, but not the qualities themselves. 



Species, hoAvever, are not in the main distinguished from their 

 allies by quantities nor by degrees; the very qualities may differ. 

 The higher animals and plants are not only taller and heavier than 

 their long- forgotten unicellular forefathers; thej^ surpass them in 

 large numbers of special characters, which must have been acquired 

 by their ancestors in the lapse of time. Hoaa^ such characters have 

 been brought about is the real question AA^ith Avhich the theory of 



