392 THE EVIDENCE OF EVOLtTTION. 



Quetelet's celebrated law of variability Avas jDublished 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 

 laAv 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 with 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 sharjDlj^ defined against one another. 

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

 the same qualities. Only with such, however, Quetelet's law is con- 

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

 ties. Moreover, the degrees of deviation are subject to reversion to 

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

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

 commonly or readily revert into one another. It is assumed that from 

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

 parable with the phenomena which are ruled by the law of probability. 



A thorough study of Quetelet's law would no doubt at once have 

 revealed the weak point in DarAvin's conception of the process of evo- 

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

 department of antliropology, and for years and years it has been 

 prominent in that science, without, however, being applied to the cor- 

 i-espondiiig phenomeua of the life of animals and of jolants. Only of 

 late has it freed itself from its bounds, transgressed tlie old narrow 

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

 the fundamental laws of living nature. 



In doing so, however, it has become the starting point for a critical 

 revieAV of the very basis of Darwin's conception of the pr.rt played by 

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

 are ruled by this law, and Avhich are bound to such narrow 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 vgij qualities may differ. 

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

 their long- forgotten unicellular forefathers; they surpass them in 

 large numbers of special characters, Avhich must have been acquired 

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

 been brought about is the i-cal cpiestion Avith Avhich the theory of 



