254 ESSENTIALS OF BIOLOGY 



qualities, by controlled matings, intensive inbreeding and so 

 on. It is unfortunate that there are few good accounts, by- 

 practical breeders, of all the trials, successes and failures by which 

 a " breed " become established, but the records of experimental 

 operations point clearly to the methods involved. These, in brief, 

 mean selection and controlled matings. Now if we are to extend 

 the experiences of the experimentalists and practical breeders, 

 so as to explain the processes of natural transformism it is necessary 

 that we insert, in wild nature, some process of controls that operate 

 in analogous ways to those practised under artificial conditions. 



86b. The Results of Mendelism do not afford an 

 Explanation of Natural Transformism. Even when we 

 accept the main results of Mendelian research there is something 

 wanting. Mutations occur. These novelties in bodily character 

 are paralleled by changes in the developmental organizations of 

 the organisms that display them and we may say, meanwhile, 

 that new developmental factors come into existence. The new 

 factors are not integrated into the developmental ensemble so 

 that they are " loose " and may assort, reassort, link, etc., at each 

 maturation of the germ-cells, or at each conjugation of the 

 gametes. This means that, with the restrictions imposed by 

 *' linkages," the organisms that result from the sexual matings 

 may display many combinations of the " loose " characters. It 

 is also plain that, by selection of the individuals that are to be 

 mated categories may become established and it is possible that 

 (within the restrictions suggested above) categories of organisms 

 displaying any desired combination of loose characters (that is, 

 characters capable of assortment and reassortment) may be 

 established. Further, under the conditions of continued control^ 

 such categories may be maintained. 



But in wild nature the conditions of controlled matings do not 

 exist (or we insert those conditions, by hypothesis into wild nature). 

 There may be " instinctive antipathies " between the individuals 

 belonging to different species, whereby they do not attempt to 

 mate, but we do not know of such antipathies between individuals 

 that differ only in respect of Mendelian characters. We may, 

 therefore, conclude that, in wild conditions there is complete 

 promiscuity of mating between Mendelian variants and so it 

 follows that there are no Mendelian categories such as may be 

 established and maintained by human artificial controls. Or, at 



