Vv 
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 
' VoL. 1 ee =) 
