"Are dreams epiphenomenal or have they Darwinian survival value? I find 'tidying the hard disk' (Evans, Crick) to be not a big enough theory."
Besides being the first truly interesting tweet I've ever read, this is a remarkable statement about the modern science of dreaming, and a surprising source of inspiration for a new generation of researchers striving to produce "bigger" theories of the nature and functions of dreaming.
The question Dawkins poses is fundamental for any kind of scientific approach to dreams. Are dreams epiphenomenal, meaning they are nothing more than accidental side-effects of the brain's activities in sleep, with no purpose or function of their own? Or do dreams have Darwinian survival value, meaning they have evolved in the course of history to play a direct causal role in the reproductive success of our species?
In short: Are dreams pointless nonsense, or do they serve an evolutionary function?
"Evans" is Christopher Evans, a British psychologist and computer scientist, who wrote Landscapes of the Night: How and Why We Dream (1983, Viking Press, posthumously edited by his son Peter Evans).
"Crick" is Francis Crick, Nobel Prize winner in 1962 with James Watson for their discovery of DNA. In 1983 Crick co-wrote a paper in the prestigious journal Nature, titled "The Function of Dream Sleep" (vol. 304, pp. 111-114).
Both Evans and Crick looked at the human brain as kind of biological computer, and this brain-computer analogy directly shaped their analysis of dreams. Evans explained the nature of dreams by developing a "computer theory, in which the brain is continually updating its vast library of programs during the off-line sleep phase." (p. 217) Crick and Mitcheson proposed that dreaming is a process of "reverse learning" or "unlearning" in which the brain cleans itself of faulty, maladaptive neural patterns that have accumulated during the day, just like a computer program that regularly scans the hard drive to find and eliminate bad circuitry. Crick and Mitchison said,
"In this model, attempting to remember one's dreams should perhaps not be encouraged, because such remembering may help to retain patterns of thought which are better forgotten. These are the very patterns the organism was attempting to damp down." (p. 114)
As highly-regarded scientists, Evans and Crick gained a great deal of public attention for their ideas about dreaming. They seemed to be expressing the proper kind of hard-headed attitude that modern, educated people should hold toward dreams.
But according to Richard Dawkins, that attitude isn't "big enough." He seems to find the brain-computer analogy too small, too narrow, too limiting as a way of accounting for the role of dreaming in human life. Dawkins does not suggest what the survival value of dreaming might be (he's already fit a lot into 144 characters!), but he has clearly opened the door to new research that treats dreaming not as a random by-product of sleep but as a potentially adaptive mode of brain-mind functioning that contributes to human survival and reproduction.
I must confess I came across Dawkins' tweet when searching for negative, dismissive quotes about dreams. I assumed, based on reading books like The Selfish Gene and The God Delusion, that Dawkins would be part of the "dreams are epiphenomena" team. To my pleasant surprise, that assumption was wrong. Even someone like Dawkins, one of the world's greatest champions of scientific reason, recognizes that computer theories of dreaming are inadequate. There's a reason no one has done anything new with Evans and Crick's ideas in the past 30 years: they don't square with the facts any more. It turns out the brain is much more complex than any computer, and dreams are doing much more in the brain than "unlearning." Ironically, the "tidying the hard drive" theory, which once seemed like the pinnacle of scientific respectability, can no longer account for the actual scientific evidence about dreaming and the brain.
Tip of the hat to Richard Dawkins for calling them the way he sees them.