OTHER THEORIES OF GERMINAL SELECTION 405 



would iindoubtedly have been more quickly eliminated than any 

 of its longer-legged relatives. 



Mutations apparently do not depend on natural selection, 

 however, for their potency in the formation of species. We must 

 recognize that whether we are willing to call them species or 

 merely varieties, some of the forms that have arisen this way 

 are entitled to specific rank, provided only that they can satisfy 

 other criteria for the limitation of species than mere morphological 

 differences. 



The Cause of Mutations. The possible cause of mutations 

 has been the subject of nuich discussion. An early view compared 

 the species to the individual in its development from infancy to 

 old age. In its period of maturity the species was supposed to 

 produce other species as the individual produces its offspring. 

 Such an analogy is attractive but hardly a soundly scientific 

 explanation. There is more reason to believe the conclusion of 

 modern geneticists that abnormal behaviour of the chromosomes 

 or modification of the genes by unexplained processes may be 

 responsible. Even this opinion, while it leaves us with a definite 

 basis for future investigation, also leaves us with a feeling that 

 we have not explained the origin of mutations; rather we have 

 merely paved the way for further study of the problem. 



Given living organisms and their several kinds of variations 

 we now know something about the processes of change which go 

 on within them, but we have not yet penetrated beyond that 

 starting point. Our progress is not discouraging for there is still 

 much to be discovered by accurate scientific study of these matters, 

 and additions are ]:)eing made to our knowledge every year. 



Weismann's Theories. Two other corollary or substitute 

 theories of evolution were proposed by Weismann, one of the 

 greatest followers of Darwin. One, the theory of germinal selec- 

 tion, is a frank attempt to meet the failure of natural selection to 

 explain the modification of organs beyond the range of importance 

 to the individual. The other, panmixia, was first developed for 

 the same purpose and later discarded in favor of germinal selection. 

 Weismann recognized that his theory of panmixia explained the 

 modification of indifferent organs to a hmited degree even though 

 he found it necessary to discard it as an explanation of evolution. 



Panmixia. The principle of panmixia is that indifferent organs, 

 since they are of no consequence to the individual, will be mingled 



