316 



CHAPTEE XXXVII. 



NATUEAL SELECTIOIT. 



IN EACH 



NATURAL AS COMPARED TO ARTIFICIAL SELECTION — TENDENCY 

 SPECIES TO MULTIPLY BEYOND THE MEANS OF SUBSISTENCE -TERMS 'SELEC- 

 TION' AND 'SURVIVAL OF THE FITTEST '—GREAT NUMBER AND VARIETY OF 

 THE NATURAL CONDITIONS OF EXISTENCE ON T;\^HICH THE CONSTANCY OR 

 VARIATION OF A SPECIES DEPENDS— ACCLIMATISATION OF SPECIES 



INTERCROSSING OF SLIGHT VARIETIES BENEFICIAL BREEDING 



INJURIOUS— WILD HYBRID PLANTS, AND OPINIONS OF LINN2EUS ON PROTEAN 

 GENERA— DE CANDOLLE ON WILD HYBRIDS— HYBRIDITY WILL NOT ACCOUNT 

 FOR SPECIAL INSTINCTS— THE SPECIES OF POLYMORPHOUS GENERA MORE 

 VARIABLE AND COMPARATIVELY MODERN— ALTERNATE GENERATION DOES 

 NOT EXPLAIN THE ORIGIN OF NEW SPECIES. 



■THE 



IN AND IK 



Nj 



iL AS COMPARED TO ARTIFICIAL SELECTION.— .Jn 



the last chapter we have spoken of the great changes which 

 man has brought about in the course of many generations 

 in the form and characters of animals and plants, by selecting 

 certain useful varieties of a species, and breeding from them 

 to the exclusion of other varieties less profitable or pleasing 



to him. 



accumulatin 



ences in successive generations until new races have been 

 formed as distinct in outward shape, and sometimes in the 



meet 



most 



from 



cies by the fertility of the offspring produced by their union. 



We may next consider the modification 



Mr 



natural selec- 



tion/ of which we gave a brief analysis in Chap. XXXY. 

 How far do the breeder, the agriculturist, and gardener, 



mnch 



►se of time, nature 

 om the original tjp 









gres 



s 



that 



insi^ 



ther 



indi' 



theiJ 

 oper 



com' 



race' 



at 1( 

 proc 

 hum 



whii 



effe 

 1 



siibs 

 of ei 

 alloi 



poiu- 



ere a 5 



soon 



pair. 



slo^r 



< 



( 



mult; 

 thirt' 



and i 

 outf 



■ the 



re 

 singi, 



In 



estf 

 the 



( 



s 



) 



