In his book Big Dreams: The Science of Dreaming and the Origins of Religion, Kelly Bulkeley looks at both research and evolutionary theory to ponder a famously intractable question: Why do we dream? The Atlantic reports.

Kelly Bulkeley: If you just look at the current science, it’s pretty clear that dreaming has a lot more psychological structure, a lot more personal meaning, a lot more cognitive sophistication than a random static point of view would suggest.

So certainly I’m waving the banner of, yes, dreams have dimensions of meaning. I’m not going to say that every dream has heaven-sent revelations or anything like that, but we’re learning a lot about what those dimensions of meaning are.

The short definition is that dreaming is imaginative play in sleep and that’s the way I think of dreaming in an evolutionary context. It’s a hardwired, neurologically-grounded process that occurs throughout our species, that has deep roots in mammalian evolution. There’s something very profound in how our minds and brains are operating during sleep and one of the ways I think it’s best to conceptualize that is that dreaming is a kind of play in a set apart from space where ordinary rules of reality are suspended temporarily and we try out different strategies, we rehearse different kinds of behavior.

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