THE CONDITIONS OF EXISTENCE AS AFFECTING 

 THE PERPETUATION OF LIVING BEINGS. 



IN the last Lecture I endeavoured to prove to 

 you that, while, as a general rule, organic beings 

 tend to reproduce their kind, there is in them, 

 also, a constantly recurring tendency to vary to 

 vary to a greater or to a less extent. Such a 

 variety, I pointed out to you, might arise from 

 causes which we do not understand ; we there- 

 fore called it spontaneous ; and it might come 

 into existence as a definite and marked thing, 

 without any gradations between itself and the 

 form which preceded it. I further pointed out, 

 that such a variety having once arisen, might be 

 perpetuated to some extent, and indeed to a very 

 marked extent, without any direct interference, or 

 without any exercise of that process which we 

 called selection. And then I stated further, that 

 by such selection, when exercised artificially if 

 you took care to breed only from those forms 

 which presented the same peculiarities of any 



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