86 BIOLOGICAL LECTURES. 



by experiment. Let phylogenic variation — a term first used 

 by Nageli ^ — include those departures from type which have 

 become constant hereditary characters in certain phyletic series 

 or even in a few generations. While all phylogenic variations 

 must originate in ontogeny or in some stage of individual 

 development, certainly a very small proportion of the innumer- 

 able ontogenic variations which we find in the examination or 

 measurement of any adult individual ever become phylogenic, 

 or constitute more than ripples upon the surface of a tide. 



This vital distinction has not been regarded hitherto. The 

 statistics of variation, as compiled by Darwin and lately by 

 Wallace, Weldon, Bateson, and others, do not take into account 

 that among phylogenic variations are others purely ontogenic 

 springing up and disappearing during individual life, owing to 

 causes connected solely with the disturbance of the typical 

 action of the hereditary mechanism during ontogeny. In other 

 words, these writers have without discrimination based upon 

 variations, which may be largely or wholly ontogenic and tem- 

 porary, the important principles of ' Fortuitous Variation ' of 

 Darwin and of ' Discontinuous Variation ' of Bateson, whereas 

 it is only the laws of phylogenic variation which are of real 

 bearing upon the problem of evolution. Take as an illustra- 

 tion of this false method the wing measurements of birds given 

 by Wallace. Why may not these be largely cases of purely 

 ontogenic variation due to influences of life habit or to some 

 purely temporary disturbance of the hereditary basis .? Above 

 all others, the Neo-Darwinians must reconsider their principle 

 of 'fortuitous variation' which has been based upon data of 

 miscellaneous ontogenic and phylogenic variations, because 

 Neo-Darwinism is essentially and exclusively a theory of the 

 survival of favorable phylogenic variations. 



One aspect of the variation problem of to-day may, there- 

 fore, be stated thus : What is the cause, nature, and extent of 



1 Die Veranderung, die gewohnlich der Vererbung gegeniiber gestellt wird, steht 

 nicht im Gegensatz zu dieser, sondern zur Constanz. In diesem Sinne heisst eine 

 Veranderung constant, wenn das Gewonnene dauernd behalten, und verganglich, 

 wenn es bald wieder preisgegeben wird. Die constante oder die phylogenetische 

 Verdiiderting . . . ist eigentlich nichts anderes als die Constitutionsanderung des 

 Idioplasmas. Theorie der Abstammungslehre, p. 277- 



