1 62 Determinate Variation and Selection 



The question of determinate variation is : Has any influ- 

 ence worked to make the mean of variation of tJie new gen- 

 eration different from that which should be expected from 

 the characters of their parents, 1 whatever the extent of varia- 

 tion may be. 



2. The assumption of Professor Osborn (loc. cit., pp. 584- 

 585), that because certain fossils show determinate prog- 

 ress, determinate evolution, therefore there must have 

 been determinate variation, seems to me defective logic. 

 It is one possibility among others, certainly, but only one. 

 And as has been said above, Chap. X. 3, instead of 

 being necessary as a support for organic selection, that 

 principle comes as a new resource to diminish the proba- 

 bility that the variations have really been determinate in 

 these cases. They may be cases of orthoplasy involving 

 organic selection working as an aid to natural selection 



1 I expressly avoid saying what this mean is, i.e., what the contribution of 

 each parent is to the average individual of their offspring ; but the work of 

 Galton goes far to establish it. Much more investigation is needed on this 

 point of making out what is indeterminate variation ; how insecure, therefore, 

 the claim that variations are determinate ! The drift of recent statistical 

 studies goes, however (so far as the writer can judge), directly to show 

 that in their distribution considered apart from their extent variations 

 follow the probability curve. They are summarized by Weldon and Daven- 

 port in the Arts, on ' Variation ' in the Diet, of Philosophy and Psychology, 

 Vol. II. ; see also the Arts. ' Gallon's Law ' (of ancestral inheritance) and 

 ' Selection ' (in biology). The following suggestions in terminology are made 

 by the present writer in the same work (art. ' Variation,' ad Jin.} : " In the 

 treatment of variation, confusion arises from failure to distinguish the follow- 

 ing forms: (a) 'indefinite' or 'fortuitous' or ' ataxic ' (variation subject to 

 * chance,' or following the law of probability) ; (/') ' definite ' or ' determinate ' 

 (variation following some other law than that of probability). The latter 

 may well be again divided into (i) 'autotaxic' (determinate variation due 

 to intrinsic vital tendencies to development, as held by all forms of vital- 

 ism), and (2) 'taxonomic' (determinate variation caused by external causes 

 of any sort)." Note added 1902. 



