LECTURE V. 



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 con- 

 stantly 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 therefore 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 per- 

 petuated 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 variety which had arisen in this manner — the 

 variation might be perpetuated, as far as we can see, 

 indefinitely. 



