TENDENCY OF SPECIES TO FORM VARIETIES. 1 1 



ciable to an uneducated eye. Selection has been methodically followed 

 in Europe for only the last half century; but it was occasionally, and 

 even in some degree methodically, followed in the most ancient times. 

 There must have been also a kind of unconscious selection from a 

 remote period, namely in the preservation of the individual animals 

 (without any thought of their offspring) most useful to each race of 

 man in his particular circumstances. The 'roguing,' as nurserymen 

 call the destroying of varieties which depart from their type, is a kind 

 of selection. I am convinced that intentional and occasional selection 

 has been the main agent in the production of our domestic races; 

 but however this may be, its great power of modification has been in- 

 disputably shown in later times. Selection acts only by the accumu- 

 lation of slight or greater variations, caused by external conditions, or 

 by the mere fact that in generation the child is not absolutely similar 

 to its parent. Man, by this power of accumulating variations, adapts 

 living beings to his wants — may be said to make the wool of one sheep 

 good for carpets, of another for cloth, etc. 



2. Now suppose there were a being who did not judge by mere ex- 

 ternal appearances, but who could study the whole internal organization, 

 who was never capricious, and should go on selecting for one object 

 during millions of generations ; who will say what he might not effect ? 

 In nature we have some slight variations occasionally in all parts; and 

 I think it can be shown that changed conditions of existence is the main 

 cause of the child not exactly resembling its parents; and in nature 

 geology shows us what changes have taken place and are taking place. 

 We have almost unlimited time; no one but a practical geologist can 

 fully appreciate this. Think of the Glacial period, during the whole 

 of which the same species at least of shells have existed; there must 

 have been during this period millions on millions of generations. 



3. I think it can be shown that there is such an unerring power at 

 work in Natural Selection (the title of my book), which selects exclu- 

 sively for the good of each organic being. The elder De Candolle, W. 

 Herbert, and Lyell have written excellently on the struggle for life; 

 but even they have not written strongly enough. Eefiect that every be- 

 ing (even the elephant) breeds at such a rate, that in a few years, or 

 at most a few centuries, the surface of the earth would not hold the 

 progeny of one pair. I have found it hard constantly to bear in mind 

 that the increase of every single species is checked during some part of 

 its life, or during some shortly recurrent generation. Only a few of 

 those annually born can live to propagate their kind. What a trifling 

 difference must often determine which shall survive, and which perish ! 



4. Now take the case of a country undergoing some change. This 

 will tend to cause some of its inhabitants to vary slightly — not but that 

 I believe most beings vary at all times enough for selection to act on 



