8 NATURAL SELECTION 



pressure is always ready, capacity of alpine plants 

 to endure other climates, think of endless seeds 

 scattered abroad, forests regaining their percen- 

 tage 1 , a thousand wedges 2 are being forced into 

 the oeconomy of nature. This requires much reflec- 

 tion; study Mai thus and calculate rates of increase 

 and remember the resistance, only periodical. 



The unavoidable effect of this (is) that many of 

 every species are destroyed either in egg or [young 

 or mature (the former state the more common)]. In 

 the course of a thousand generations innnitesimally 

 small differences must inevitably tell 3 ; when unusu- 

 ally cold winter, or hot or dry summer comes, then 

 out of the whole body of individuals of any species, 

 if there be the smallest differences in their structure, 

 habits, instincts [senses], health &c., (it) will on 

 an average tell; as conditions change a rather larger 

 proportion will be preserved: so if the chief check 

 to increase falls on seeds or eggs, so will, in the 

 course of 1000 generations or ten thousand, those 

 seeds (like one with down to fly 4 ) which fly furthest 

 and get scattered most ultimately rear most plants, 

 and such small differences tend to be hereditary like 

 shades of expression in human countenance. So if 

 one parent (?) fish deposits its egg in infinitesimally 

 different circumstances, as in rather shallower or 

 deeper water &c., it will then (?) tell. 



Let hares 5 increase very slowly from change of 

 climate affecting peculiar plants, and some other 



^j \ j. * 



(illegible) rabbit decrease in same proportion [let 

 this unsettle organisation of], a canine animal, who 



1 Origin, Ed. i. p. 74, vi. p. 91. "It has been observed that the trees 

 now growing on... ancient Indian mounds... display the same beautiful 

 diversity and proportion of kinds as in the surrounding virgin forests." 



2 The simile of the wedge occurs in the Origin, Ed. i. p. 67 ; it is deleted 

 in Darwin's copy of the first edition : it does not occur in Ed. vi. 



3 In a rough summary at the close of the Essay, occur the words : 

 " Every creature lives by a straggle, smallest grain in balance must tell." 



4 Cf. Origin, Ed. i. p. 77, vi. p. 94. 



5 This is a repetition of what is given at p. 6. 



