In a paper published last month in the journal Nature Reviews Neuroscience, Dr. J. Allan Hobson, a psychiatrist and longtime sleep researcher at Harvard, argues that the main function of rapid-eye-movement sleep, or REM, when most dreaming occurs, is physiological. The brain is warming its circuits, anticipating the sights and sounds and emotions of waking.Apparently nobody knows which theory is correct, but they are all pretty sure that Freud's theories were nonsense.
It goes on:
These novel ideas about dreaming are based partly on basic findings about REM sleep. In evolutionary terms, REM appears to be a recent development; it is detectable in humans and other warm-blooded mammals and birds.Recent development?! I thought that mammals and birds were supposed to have evolved from reptiles maybe 200 million years ago. So is this trying to say that animals have only been dreaming for 200 million years? That is called "recent"?
Update: This evolutionist says 315 million years ago.