Tin-: EH i; H BXIS1 



many more* individual- an- U.rn than can potMhly sur- 

 The result i> that those born with rtaiii weak- 

 nesses or und.-r unfavorable condition- an- the ones u 

 are most likely to .11.-, while those possessing greater 



'.orn ni; orahle conditions are the ones 



it is that then* tends to be 



a -in \ i\al of tli tit. Nittm.-, so to say, selects the best 







It is a self-evident fact that tin- amount of -par,- upon 

 limited. At tir-t thought it is not so evident 



livinir things tend to multiply i .-al pro- 



LM-.--i.ii. Hut thr truth of this prim-iplr in eanily demon- 

 -trat. ! I,'.. main's tflls us that if tin- y of a single 



pair of rh'phants. \\lii.-h : nv t he slowest breeding of ani- 

 mals, were allowed to reach maturity and propa^a? 

 750 years there would he living 19,000,000 descendants. 1 



->or Metc-alf has computed the following table baaed 

 upon th ase of the common robin. Sup 



posin.ir that tin- yearly otTspring of each pair of 



on the av. lii.'h is below tin* usual number, 



pair uf l.inls would hav four yuiiLr in the 

 first generation. The second year they would have four 

 more young, and their youm: of the fir- . mating. 



would have "ung, four for each of the two \ 



In twenty \ he descvndant> of the original pair 



would nuiii' r twenty l.illi- 



is should make it clear that the earth could not >up- 

 port the progeny of -\ -n a single sp the natural 



increase were allowed to go unchecked. 1 



But in the case of the rohins. nmn- hirds die each year 

 than livo because we find that the number remains con- 



Jiianem, O. J. Dartritt amd After Dancim. I Tk* Daririmiam Theory, 

 1001. p. 261. 

 tMetcmlf. op. '!.. p. 14. 



