42 THE CASE AGAINST EVOLUTION 



being the subsequent product of the interplay of genetic fac- 

 tors and environmental stimuli, dependent upon, and expres- 

 sive of, both. 



Variation, therefore, may be based upon a change in the 

 germ plasm, or in the environment, or in both. If it rests 

 exclusively upon an extraordinary change in the environ- 

 mental conditions, the resulting modification is non-inherit- 

 able, and will disappear so soon as the exceptional environ- 

 mental stimulus that evoked it is withdrawn. If, on the 

 contrary, it is based upon a germinal change, it will manifest 

 itself, even under ordinary, i.e. unchanged or uniform envi- 

 ronmental influence. In this case, the modification is inherit- 

 able in the sense that it is the specific effect of a transmissible 

 germinal factor, which has undergone alteration. 



As we have seen in the foregoing chapter, there are three kinds 

 of germinal change which result in "inheritable" modifications. 

 The first is called factorial mutation, and is initiated by an 

 alteration occurring in one or more of the chromosomal genes. 

 The second is called chromosomal mutation, and is caused 

 by duplication (or reduction) of the chromosomes. The third 

 may be termed recombination, one type of which results from 

 the crossover or exchange of genes between pairing chromo- 

 somes ("pseudomutation"), the other from random assortment 

 in accordance with the Mendelian law of the independence of 

 allelomorphic pairs. This so-called 'Random assortment of 

 the chromosomes" is the result of the shuffling and free deals 

 of the chromosomal cards of heredity which take place twice in 

 the life-cycle of organisms: viz. first, in the process of gametic 

 reduction (meiosis) ; second, in the chance meeting of vari- 

 ously-constituted sperms and eggs in fertilization. A mis- 

 chance of the first of these "free deals" is bewailed in the 

 following snatch from a parody belonging to the Woods Hole 

 anthology. 



"Oh chromosomes, my chromosomes, 

 How sad is my condition! 

 My grandsire's gift for writing well 



