XI.] SPECIFIC GENESIS. 241 



being more or less easily supplied. There is, however, no 

 similar evidence at present as to higher forms ; while, as 

 we have seen in Chapter VII., there are a priori con- 

 siderations which militate against their being similarly 

 evolved. 



The presence of wild varieties and the difficulty which 

 often exists in the determination of species are sometimes 

 adduced as arguments that high forms are now in process 

 of evolution. These facts, however, do not necessarily 

 prove more than that some species possess a greater varia- 

 bility than others, and (what is indeed unquestionable) that 

 species have often been unduly multiplied by geologists 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. 



With regard to the lower organisms, and supposing 

 views recently advanced to become fully established, there 

 is no reason to think that the forms said to be evolved were 

 new species, but rather reappearances of .definite kinds 

 which had appeared before and will appear again under the 

 same conditions. In the same way, with higher forms simi- 

 lar conditions must educe similar results, but here practically 

 similar conditions can rarely obtain because of the large part 

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

 highly-organized 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 sever- 

 ally 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 to how far variations in the eccentricity in the 

 earth's orbit together with the precession of the equinoxes 

 have produced changes in climate. Mr. Wallace has pointed 

 11 



