276 Heredity. 



the many physiological influences to which mental development 

 is subject; but it is a mistake to suppose that this implies a 

 metaphysical solution. It is true that by the law of heredity, the 

 higher is subordinated to the lower ; but it would be to go beyond 

 experience, and to risk a wholly gratuitous assertion, to assert 

 that heredity absolutely proves the dependence of the higher on 

 the lower, of the better on the worse. 



IL 



Thus to the question originally stated, ' What is the cause oi 

 psychological heredity?' we may reply, not transcending the 

 domain of experience, 'Physiological heredity.' Because the 

 organism, and in particular the nervous system, is transmissible, 

 therefore the various modes of sensation, instinct, imagination, 

 intellect, sentiment, are also transmissible. Psychological heredity 

 being thus referred to physiological, as to its immediate cause, 

 we have to inquire the cause of this latter, and to ask how 

 physiological heredity is produced. 



In the present state of biology we cannot hope for any positive 

 explanation of heredity. We are reduced to hypothesis. The 

 most recent of these, and the best wrought out, is that of 

 Darwin, in his Variation of Animals and Plants under Domesti- 

 cation, the broad outlines of which are found in Spencer's 

 Principles of Biology. It bears the name of pangenesis. 



To understand it aright, we must first remember that con- 

 temporary physiology looks on every living body, regardless 

 of its unity, as an aggregate of cells in prodigious numbers, each 

 of which has a life of its own, and possesses the fundamental 

 properties of life nutrition, by which it is ever assimilating and 

 disassimilating ; evolution, by Avhich it grows in volume and be- 

 comes complicated into more perfect and more numerous parts; 

 reproduction, in virtue of which each cell can produce another, 

 that cell a third, and so on. Virchow has shown that a single 

 cell may be diseased ; so that it may be said that this automatic 

 element plays in the organism the same part as the individual in 

 the State, having a certain degree of independence, though con- 

 stituting an integral part of the body social. 



