320 Heredity. 



point, which is not so much a consequence of heredity as the law 

 itself, under its most perfect form, we pass on to the consideration 

 of another still more curious point, not so well known, and more 

 difficult to prove, but which, from its bearing on intelligence, con- 

 stitutes an important consequence of heredity. It may thus be 

 stated under an ideal form, that is, without taking into account the 

 exceptions : heredity, acting by way of accumulation, augments 

 intelligence in successive generations, and thus makes it capable 

 of fresh developments. 



This we will now endeavour to prove. 



We will first point out the physiological grounds of the fact 

 under consideration. It is well known that every organ is 

 developed by exercise : in the blacksmith the muscles of the 

 arms ; in the pedestrian, those of the legs. The organ produces 

 the function, but the function in turn reacts on the organ and 

 develops it We can scarcely doubt that this holds good with 

 regard to the brain, that it grows by exercise, and that this aug- 

 mentation is transmissible by heredity. Dr. Brocas, on the 

 strength of various researches, says that the capacity of the skull, 

 and consequently the volume of the brain, corresponds with the 

 degree of intelligence of the different races : the largest are found 

 in the white race, then in the Caucasian, next in the negroes of 

 Africa the Australian negro holds the last rank. Albert, of 

 Bonn, says that having dissected the brains of several persons 

 who had for years been accustomed to mental work, he found in 

 all the cerebral substance very firm, and the grey matter and the 

 convolutions highly developed. * The augmentation of the mass 

 of the brain,' he says, ' is proved partly by the difference existing 

 between cultured and uncultured people, and partly by the in- 

 creased volume of brain which results from the progress of 

 civilization in Europe ; an increase which accumulates, by reason 

 of heredity, in a degree which admits of demonstration.' (Mit 

 Hiilfe der Vcrcrbung sich so writ snmmiri, doss es constatirt werdcn 

 kann.) In fact, we find that among the educated classes the 

 size of the head is usually large, and that the contrary is the 

 case among the uneducated. Finally, there is a fact which directly 

 concerns the question in hand : excavations made in cemeteries 

 show that the size of skulls has increased since the Middle Ages. 



