Why dream? A Conjecture on Dreaming

I propose that the need for sleep and the occurrence of dreams are intimately linked to the physical processes underlying the continuing replacement of cells and renewal of biomolecules during the lives of higher organisms. Since one major function of our brains is to enable us to react to attack, there must be truly compelling reasons for us to take them off-line for extended periods, as during sleep. I suggest that most replacements occur during sleep. Dreams are suggested as part of the means by which the new neural circuitry (I use the word in an informal sense) is checked.