It was not till I was a young man, at college, that I got any clew to the significance of my dreams, and to the cause of them. Up to that time they had been meaningless and without apparent causation. But at college I discovered evolution and psychology, and learned the explanation of various strange mental states and experiences. For instance, there was the falling-through-space dream—the commonest dream experience, one practically known, by first-hand experience, to all men.

This, my professor told me, was a racial memory. It dated back to our remote ancestors who lived in trees. With them, being tree-dwellers, the liability of falling was an ever-present menace. Many lost their lives that way; all of them experienced terrible falls, saving themselves by clutching branches as they fell toward the ground.

Now a terrible fall, averted in such fashion, was productive of shock. Such shock was productive of molecular changes in the cerebral cells. These molecular changes were transmitted to the cerebral cells of progeny, became, in short, racial memories. Thus, when you and I, asleep or dozing off to sleep, fall through space and awake to sickening consciousness just before we strike, we are merely remembering what happened to our arboreal ancestors, and which has been stamped by cerebral changes into the heredity of the race.

There is nothing strange in this, any more than there is anything strange in an instinct. An instinct is merely a habit that is stamped into the stuff of our heredity, that is all. It will be noted, in passing, that in this falling dream which is so familiar to you and me and all of us, we never strike bottom. To strike bottom would be destruction. Those of our arboreal ancestors who struck bottom died forthwith. True, the shock of their fall was communicated to the cerebral cells, but they died immediately, before they could have progeny. You and I are descended from those that did not strike bottom; that is why you and I, in our dreams, never strike bottom.