THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 283 



and collected more readily than those which do not. A certain observer, for 

 example Cope, starts with a predisposition for the theory of the transmission of 

 acquired characters, we will say. His studies are confined to anatomy, animal 

 mechanics, and palaeontology; he does not at first concern himself about heredity ; 

 he arrives perhaps at an erroneous conception of the factors of evolution. The 

 fallacy of Lamarck, Spencer, Cope, and all other Lamarckians, if it be a fallacy, 

 is the time-honored post hoc ergo propter hoc. The failure of some ultra-Dar- 

 winians has been the equally ancient one of the " undistributed middle" or 

 ab uno disce omnes: e. g. } there are modes of evolution, selection explains some 

 modes of evolution; all modes of evolution are explained by selection. 



Or the observer, for example, De Vries, is a master of botany and of the experi- 

 mental method, well grounded in heredity, cytology, and in experiment alism. 

 He has not perhaps looked sufficiently into the facts of anatomy and pakeontology ; 

 he arrives perhaps at a too comprehensive application of the particular modes 

 of change which he observes. 



From these illustrations we realize that the changes which the different 

 classes of observers see going on are simply the modes of evolution; the underlying 

 causes of these changes can, in our opinion, only be discovered through a syn- 

 thesis of the phenomena as observed by all the various classes of observers. It 

 is obvious that any general theory of the causes of evolution must not be incon- 

 sistent with any of the well attested modes of evolution. We must keep clearly 

 in mind that we have accumulated a vast amount of exact knowledge about the 

 modes of evolution and comparatively little about the sequence of causes and 

 effects. 



The discordance of opinion so conspicuous today, which is entirely due, 

 as we believe, to the diversity of the gateways through which the phenomena 

 have been approached, is paralleled by the apparent but not real discordance 

 in the history of successive theories. 



The chief gateways or materials of observation have been the predisposing 

 sources of these successive "evolution theories." There are only four of these 

 gateways, namely, environment, ontogeny, selection, and heredity. The first 

 explorers, Buff on and Treviranus entered through environment. Lamarck, 

 Spencer, and Cope entered chiefly through ontogeny, Darwin and Wallace 

 entered chiefly through selection. Similarly Weismann and Bateson, entering 

 through the gateway of heredity reach an equally exclusive standpoint. 



Paradoxical as it may appear these observers are at once right and wrong. 

 Each complex of conditions is contributary ; no complex of conditions is ex- 

 clusively operating. This, we shall attempt to show, is because the inseparable 

 action of all the four factors results either in : (1) the leading action of one factor 

 in the building up of a new character or the modification of an existing character, 

 or (2) in the combined and simultaneous action of all the factors on different 

 groups of characters to bring about a harmonious and correlated result. 



Finally, characters are to be understood in two senses: 



