TNI DOLE i"i; BUS -; 



three. The sp- not HO easily teen 



from above. nni\ ,, h ,. ,,r tliom wan killed. Tlaih tin- 

 mere chance of coat N-r was a de< u-tor in .! 

 iermining which cl> diould In time it i 



.!!' that more of the black ani \\hitechickenawould 



l.-.l lis hirds y tin* spotted chickens 



would be left. Their offspring \\ould tend to inherit 

 spotted coat ami hence surviv.-. All offspring 

 which varied from thi- (\|M- in (In- lir.--t inn ,,f 

 whitr coat or a Mark mat \\miM IN- lik-ly to IH- kilh-tl anil 

 leave no black or \\hit,- .nati-.l proirniN. Kvi-ntuully we 

 might have only a spott.-.i \ ..f cliick-ns in this 



Thi> is an excellent illustration of tin- principle 

 of natural selection. 



Where the characters of an iulmhiting species show 

 great variation we conclude that th r ), a .s not been 

 rigorous selection with reference to that rhara 



is, the trait in |in'stin is one which, at thr tiun- 

 thrr of grc. advan- 



tage to those who possess it. It \\.-i- lly acquired 



or pn-srr\r,i became it was favorahlr, hut some change 

 has been wrought which makes it of inditT. -n-nt value. 

 r hand if any character shows very sliirht 

 variation as between a large numhrr of the sp<-ci<g, we 



ud<> that selection with to it has been 



severe; that is, tin- trait in ju--ti..n -ives positive ad- 

 vantage. Thus, before the coining of the crows, coat 

 color in chickens was of inditlVivnt value for survival 

 and there was wide variation fr,, m white to black. Bat 

 with the coming of the birds of pr lit ions 



changed and coat color had a positive survival val 

 it were inconspicuous. The wid. \ n soon dis- 



k and white chickens wore killed off) 



