Oh, the images that C. S. Lewis can create! This intriguing comparison between the appetite for food and the appetite for sex creates one of the more memorable passages from Mere Christianity:
The biological purpose of sex is children, just as the biological pupose of eating is to repair the body. Now if we eat whenever we feel inclined and just as much as we want, it is quite true most of us will eat too much; but not terifically too much. One man may eat enough for two, but he does not eat enough for ten. The appetite goes a little beyond its biological purpose, but not enormously. But if a healthy young man indulged his sexual appetite whenever he felt inclined, and if each act produced a baby, then in ten years he might easily populate a small village. This appetite is in ludicrous and perposterous excess of its function.
Or take it another way. You can get a large audience together for a strip-tease act – that is, to watch a girl undress on the stage. Now suppose you come to a country where you could fill a theatre by simply bringing a covered plate on to the stage and then slowly lifting the cover so as to let everyone see, just before the lights went out, that it contained a mutton chop or a bit of bacon, would you not think that in that country something had gone wrong with the appetite for food?