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Show lOG TilE PERPETUATION OF LIVING BEINGS. If vou carry in your mind's eye these four varieti~s of pigeons, you will bear with you as good a notion as you can have, perhaps, of the enormous extent to which a deviation frmn a primitive type may be carried by means of this process of selective breeding. 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 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 therefore called it spontaneous; and it might come into existence as a definj te 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 variety which had arisen in this manner-the variation might be perpetuated, as far as we can see, indefinitely. p 2 |