34 DARWimANA. 



artificial selection? Mr. Darwin thinks that there is; 

 and Naticral Selection is the key-note of his discourse. 



As a preliminary, he has a short chapter to show 

 that there is variation in IN^atui'e, and therefore some- 

 thing for natural selection to act upon. He readily 

 shows that such mere variations as may be directly 

 referred to physical conditions (like the depauperation 

 of plants in a sterile soil, or their dwarfing as they 

 approach an Alpine summit, the thicker fur of an ani- 

 mal from far northward, etc.), and also those indi- 

 vidual differences which we everywhere recognize but 

 do not pretend to account for, are not separable by any 

 assignable line from more strongly-marked varieties ; 

 likewise that there is no clear demarkation between 

 the latter and sub-species, or varieties of the higest grade 

 (distinguished from species not by any known incon- 

 stancy, but by the supposed lower importance of their 

 characteristics) ; nor between these and recognized 

 species. " These differences blend into each other in 

 an insensible series, and the series impresses the mind 

 with an idea of an actual passage." 



This gradation from species downward is well made 

 out. To carry it one. step farther upward, our author 

 presents in a strong light the differences which prevail 

 among naturalists as to what forms should be admit- 

 ted to the rank of species. Some genera (and these 

 in some^ countries) give rise to far more discrepancy 

 than others; and it is concluded that the large or 

 dominant genera are usually the most variable. In a 

 flora so small as the British, 182 plants, generally 

 reckoned as varieties, have been ranked by some bot- 

 anists as species. Selecting the British genera which 



