The Republic by Plato Part 5 Page 35

From the best.

And do you take the oldest or the youngest, or only those of ripe age?

I choose only those of ripe age.

And if care was not taken in the breeding, your dogs and birds would greatly deteriorate?

Certainly.

And the same of horses and animals in general?

Undoubtedly.

Good heavens! my dear friend, I said, what consummate skill will our rulers need if the same principle holds of the human species!

Certainly, the same principle holds; but why does this involve any particular skill?

Because, I said, our rulers will often have to practise