258 TUE GENESIS OF SPECIES. [Ctiap. 



of evolution. These facts, however, do not necessarily 

 prove more tlian that some species possess a greater vari- 

 ability than others, and (what is indeed unquestionahle) 

 that species have often been unduly multiplied by geo- 

 logists and botanists. It may be, for example, that Wagner 

 was right, and that all the American monkeys of the genus 

 cebus may be reduced to a single species, or to two. 



AVith regard to the lower oi^^anisms, and supposing views 

 recently advanced to become fully establislicd, there is no 

 reason to tliink tliat the forms said to be evolved were new 

 species, but mther reappearances of definite kinds which 

 had appeared before and will appear again under the same 

 conditions. So with higher forms, similar conditions must 

 educe similar results ; but here practically similar condi- 

 tions can rarely ol)tain, because of the large part which 

 " descent " and " inheritance " always play in such highly 

 oriianized forms. 



Still it is conceivable that different combinations at 

 different times may have occasionally the same outcome, 

 just as the multiplications of different numbers may have 

 severally the same result. 



There are reasons, however, for thinking it possible that 

 the human race is a witness of an exceptionally unchanging 

 and stable condition of things, if the calculations of Mr. 

 Croll are valid as tu Ikjw far variations in the eccentricity 

 in the earth's orbit, together with the precession of the 

 e(|uinoxes, liave produced changes in climate. Mr. Wallace 

 has pointed out ^ that, as during the last G0,000 years 



1 See Nature, ^March 3, 1870, ]>. 454. Mr. "Wiillacc says (referring to 

 Mr. Croll's paper in the PJiil. M<ig.), "As we are now, and have been for 

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

 (hiring that time may be no iruasurc of the rate that Juts general! y obtained 

 ill past geological epochs." 



