242 THE GENESIS OF SPECIES. [CHAP. 



out x that the last 60,000 years having been exceptionally 

 unchanging as regards these conditions, specific evolution 

 may have been exceptionally rare. It becomes, then, pos- 

 sible to suppose that for a similar period stimuli to change in 

 the manifestation of animal forms may have been exception- 

 ally few and feeble that is, if the conditions of the earth's 

 orbit have been as exceptional as stated. However, even if 

 new species are actually now being evolved as actively as 

 ever, or if they have been so quite recently, no conflict 

 thence necessarily arises with the view here advocated. 

 For it by no means follows that if some examples, of new 

 species have recently been suddenly produced from individ- 

 uals of antecedent species, we ought to be able to put our 

 fingers on such cases ; as Mr. Murphy well observes 2 in a 

 passage before quoted, " If a species were to come suddenly 

 into being in the wild state, as the Ancon sheep did under 

 domestication, how could we ascertain the fact? If the 

 first of a newly-born species were found, the fact of its dis- 

 covery would tell nothing about its origin. Naturalists 

 would register it as a very rare species, having been only 

 once met with, but they would have no means of knowing 

 whether it were the first or last of its race." 



But are there any grounds for thinking that in the gen 

 esis of species an internal force or tendency interferes, co- 

 operates with, and controls the action of external con- 

 ditions ? 



It is here contended that there are such grounds, and 

 that though inheritance, reversion, atavism, Natural Selec- 

 tion, etc., play a part not unimportant, yet that such an 



1 See Nature, March 3, 1870, p. 454. Mr. Wallace says (referring to 

 Mr. Croll's paper in the Phil. Mag.}, " As we are now, and have been for 

 60,000 years, in a period of low eccentricity, the rate of change of species 

 during that time may be no measure of the rate that has generally obtained 

 in past geological epocJis" 



2 " Habit and Intelligence," vol. i., p. 344. 



