276 DARWINISM TO-DAY. 



in that it is obvious that selection also produces ortho- 

 genetic evolution, that is, evolution along definite lines; 

 that in fact it can produce no other kind of 

 Orthogenesis evolution. To attribute orthogenetic results to 



contrasted with . . . , 



orthoselection, natural selection is quite right, and some one has 

 proposed the name orthoselection to distinguish 

 orthogenetic evolution as produced by selection from such 

 results produced independently, or at least partly inde- 

 pendently of selection, that is produced in accordance with 

 any one or more of the so-called theories of orthogenesis. 

 All this latter kind of orthogenesis is distinguished from 

 orthoselection in that it presumes all or most of the indi- 

 viduals of successive generations to be modified, to vary, 

 that is, in a similar manner as a result of factors, intrinsic 

 or extrinsic, producing determinate variation. This is 

 plainly different from orthoselection, in which definite lines 

 of development are produced by the eradication, through the 

 rigour of selective struggle, of all other lines. Variation 

 may be wholly fortuitous, miscellaneous, indeterminate ; but 

 selection permits only certain kinds of variation to persist, 

 to accumulate. In true orthogenesis the variation, and 

 hence the lines of modification, are predetermined. It seems 

 obvious, however, to any believer in natural selection that 

 sooner or later the fate of these lines of development will 

 come into the hands of selection. And most orthogenesists 

 do indeed admit this. But it is precisely in the making of 

 a start in modification that orthogenesis fills a long-felt 

 want, and if capable of proof, should be gladly received by 

 Darwinians as an important auxiliary theory in the ex- 

 planation of modification, species-forming, and descent. 



The first of these theories of orthogenesis has just been 

 explained, for Lamarckism may be looked on as an expla- 

 nation of orthogenetic evolution based on the perpetuation 

 and accumulation of the effects of use, disuse, and the 

 direct effects of functional stimuli. Roux's battle of the 



