OLD THEORIES OF HEREDITY 395 



So far as the idea persists in the minds of civilised men, it 

 is so much purified and sublimed that, if it does not appeal to 

 the student of science as what he would call true, it is at least 

 such that he cannot wisely call it false. For we believe in mosaic 

 or ancestral inheritance, and though we know that this has 

 a definite material basis, we have no warrant for denying that 

 this has also its metakinetic or spiritual aspect. In any case, 

 there is more than a metaphor in such phrases as " the hand of 

 the past," or " the beast in the man." 



(b) " Metaphysical " Theories. For a time, especially in the 

 latter half of the eighteenth century, it was the custom to appeal 

 to vires formativa, " hereditary tendencies," and " principles 

 of heredity," by aid of which the germ was supposed to grow 

 into the likeness of its parents. It was in part the old story of 

 explaining the working of the clock by " the principle of horo- 

 logity," and in part a pedantic way of saying " We don't know." 



Nor need we sneer at our predecessors in this respect, for the 

 tendency to resort to verbal explanations is hardly to be driven 

 from even the scientific mind except by severe intellectual as- 

 ceticism. And in so far as it expresses a respectful ignorance, a 

 consciousness of the complexity of the problem, an awareness 

 that we have still to use x (the power of life) in our biological 

 equations, such " metaphysical " mist is perhaps preferable to 

 the frost of a materialism which blasts the buds of wonder and 

 gives an illusory clearness to the vision. 



Although William Harvey (1578-1657), working " in the 

 harness of Aristotle," maintained that " all animals are in some 

 sort produced from eggs," he at the same time believed in spon- 

 taneous generation as firmly as his master did. Although he 

 maintained that the living creature begins in an apparently 

 simple primordium in which " no part of the future offspring 

 exists de facto, but all parts inhere in potentia" he was quite 

 unable to suggest or give any scientific account of the primor- 

 dium and its powers of development. He was forced to fall 



