KEGRESSION 87 



regressive or progressive, and as far as we know the chances 

 of its being the one or the other are equal. But while all 

 regressive variations trend in one direction, a progressive 

 variation may trend in any one of an infinite number of 

 directions. It need not necessarily constitute an extension of 

 the previous evolution ; it may even constitute a reversal of it, 

 as in those cases of which reversed selection takes advantage. 1 

 It is, of course, conceivable that the germ-plasm contains 

 ancestral units discrete particles which " struggle " to- 

 gether during the development of the individual, and are 

 suppressed, in which case they are rendered latent, or are 

 victorious, in which case they are expressed in his characters. 

 But it is always dangerous and unscientific to seek to explain 

 by unknown forces phenomena which can be sufficiently ex- 

 plained by forces already known. All the phenomena of 

 reversion are explainable by failure of recapitulation. All 

 the phenomena of regressive evolution are explainable by the 

 selective action of bi-parental reproduction. 



148. Every complex individual, as we know, varies in a 

 thousand ways, great and small, from its parent ; but only 

 here and there is a variation useful. The useful variations, 

 in proportion to their usefulness, are preserved and, in 

 succeeding generations, are accentuated by Natural Selection. 

 Of the useless variations some may be rendered latent, but 

 the vast majority are immediately planed away by reversion 

 directed by bi-parental reproduction. Most of them, being 

 minute, disappear in the next succeeding generation; but 

 even when they are comparatively large, a few generations 

 suffice to procure their disappearance. Even should a series 

 of individuals, having a useless variation in common, happen 

 to mate and have offspring who vary so that the character is 

 more and more accentuated, yet since the tendency towards 

 reversion is greater than towards progression, a time surely 

 comes when, perhaps in a single generation, the whole of the 



1 The fact that regressive variations are all in one direction, whereas 

 a progressive variation may trend in any one of an infinite number of 

 directions, would seem to indicate that regression is inevitable in the 

 mere absence of Natural or Artificial Selection. But this contention, 

 which has frequently been used by the present writer, will not bear close 

 examination. A progressive variation, no matter in what direction, is 

 still a progressive variation. A corresponding act of regression of no 

 greater magnitude will do no more than eliminate it. What does render 

 regression inevitable in the absence of Natural or Artificial Selection is, 

 first, the fact that regressive variations tend to be of greater magnitude 

 than progressive variations, and, second, the fact that ancient characters 

 are prepotent over less ancient characters. 



