340 



its presence and its absence. Hence hie well-known Presence and Absence 

 theory. In this case (T) is allelomorph ic to its absence (t). The inheritance 

 of combs in chickens is a beautiful application of such a conception. Muta- 

 tions according to this theory appear as the result of losses. 



Bateson pushed this idea to its logical conclusion in his Melbourne ad- 

 dress where he speculates on the possibility that evolution has come aboul 

 by the loss of something. These somethings he assumes to he inhibitors. 

 (Science, August 28, 1914). 



. . . As I have said already, this is no time for devising theories <>l 

 evolution, and I propound none. But as we have got to recognize that there 

 has been an evolution, that somehow or other the forms of life have arisen 

 from fewer forms, we may as well see whether we are limited to the old view 

 that evolutionary progress is from the simple to the complex, and whether 

 after all it is conceivable that the process Avas the other way about. 



. . . At first it may seem rank absurdity to suppose that the prim- 

 ordial form or forms of protoplasm could have contained complexity enough 

 to produce the divers types of life. 



. . . Let us consider how far we can get by the process of removal 

 of what we call 'epistatic" factors, in other words those that control, mask, 

 or suppress underlying powers and faculties. 



... I have confidence that the artistic gifts of mankind will prove 

 to be due not to something added to the make-up of an ordinary man, but to 

 the absence of factors which in the normal person inhibit the development 

 of these gifts. They are almost beyond doubt to be looked upon as releases 

 of powers normally suppressed. The instrument is there, but it is "stopped 

 down." The scents of flowers or fruits, the finely repeated divisions that give 

 its quality to the wool of the merino, or in an analogous case the multiplicity 

 of quills to the tail of the fantail pigeon, are in all probability other examples 

 of such releases. 



. . . In spite of seeming perversity, therefore, we have to admit 

 that there is no evolutionary change which in the present state of our knowl- 

 edge we can positively declare to be not due to loss. When this has been con- 

 ceded it is natural to ask whether the removal of inhibiting factors may not 

 be invoked in alleviation of 'the necessity which has driven students of the 

 domestic breeds to refer their diversities to multiple origins." 



Another idea as to the way these factors may find expression in the germ 

 cells has been advanced by Morgan under the heading of Multiple Allelo- 



