Our story starts with an octopus. Heidi, the octopus, who usually rushes to greet her keepers, is now still — she’s sleeping. But something is not still: her color. Heidi changes colors from one to the other, shifting patterns and shades as she drifts further into sleep.

But is Heidi really dreaming?

Most pet owners will tell you they’ve seen their furry friend dreaming — moving their paws and maybe even making sounds. But scientists are not so quick to jump to conclusions.

Heidi’s color-shifting may be telling a story of her sleeping states, as may also be the case with our sleeping pets, but calling those states ‘dreams’ is a leap many scientists are wary to take and, oftentimes, they dance around it. Understandably, scientists want to be cautious when describing such phenomena, so they use terms like ‘oneiric behavior’ or ‘episode recalling’ — but this obscures some of the deepest and most pressing questions.

David M. Peña-Guzmán, a philosopher of science at San Francisco State University, wants us to tackle it head-on. In his enticing book When animals dream, the author takes on the question of animal dreams directly, and his conclusions could have deep implications for how we perceive animals.

When Animals Dream: The Hidden World of Animal Consciousness
by David M. Peña-Guzmán
Princeton University Press // Buy on Amazon

Diving into dreams

Dreams are complex mental states that are often defined as an altered state of consciousness that occurs during sleep. Already, you can probably see why that can be problematic. Dreams offer a bizarre window into our consciousness, but if dreams are so intricately linked to consciousness, and animals dream, then we have to start attributing some level of consciousness to animals as well (and indeed, some researchers are saying exactly this).

This isn’t exactly a new idea. Charles Darwin famously said that “As dogs, cats, horses, and probably all the higher animals, even birds [..] have vivid dreams we must admit that they possess some power of imagination.” But from the early 1900s to 1980s, our understanding of animal consciousness was at a standstill or even regress — thankfully, we are starting to break free from that.

Research is increasingly showing that the inner world of animals is nowhere near as dull and colorless as we once thought, and mental processes like dreaming are not at all restricted to humans alone.

But it’s impossible to know exactly what goes on in the mind of an animal, so how can you prove an animal is dreaming?

First, you start with external clues. Dreams largely occur during a phase of sleep called Rapid Eye Movement (REM), but not all animals experience REM — so you focus on those that do. Reptiles, birds and mammals all experience deep sleep, but many reptiles don’t experience REM, so it helps to narrow things down a bit. From there on, Peña-Guzmán compiled some convincing anecdotes of animals seemingly experiencing dreams.

Take the young elephant Ndume in Kenya, for instance. His family had been slaughtered by poachers, and the elephant would wake up crying and showing signs of night terror. Perhaps even more startling is the case of Washoe, a chimpanzee at Central Washington University who was taught sign language and seemed to use it while sleeping. These examples (and many more) already suggest that something is happening in the minds of animals as they sleep.

Then, you can also have carefully designed lab experiments to study dreams. Neurological measurements taken during animal sleep or during key phases linked to this sleep can help researchers get a glimpse of what is going on inside animals’ brains. Zebra finch, for instance, appear to be ‘practicing’ their songs when they’re asleep — and getting better at it. Some, more invasive experiments altered neural pathways of cats, showing how this affects their behavior and sleep patterns.

If you take all this evidence (which Peña-Guzmán does), you can make a compelling case for animal dreams. But you can’t really prove it — at least not biologically.

A mind that dreams is a conscious one

Philosophically, Peña-Guzmán’s case is very compelling. But proving something like this beyond the shadow of a doubt is extremely difficult.

Biologists, even those conducting the research that Peña-Guzmán cites in When animals dream, are wary of anthropomorphization — that’s why they end up so reluctant to even mention the word ‘dream’ in relation to animals. Darwin and his peers didn’t have this concern, but the period that followed after, where scientists thought they had a good grasp on animal cognition (but didn’t) established this reluctance and a de facto moratorium on animal dream discussion. Peña-Guzmán argues this is nothing more than a delusion.

 “In an act of collective self-delusion,” Peña-Guzmán writes, “we convinced ourselves that [animals] could not possibly have what we have: a meaningful inner world.”

It’s not hard to understand why some scientists would be wary of this idea, because the implications of it would be huge: not just for animal science, but for how we deal with animals in general.

In recent years, scientists have shown more and more evidence that the cognitive abilities of animals are much higher than we suspected. It’s not just dolphins and primates — birds, pigs, insects, even some fish show signs of elevated cognitive abilities. That isn’t very troubling in itself (though it certainly makes it harder to justify eating an animal that has an intellect). But if we were forced to reconcile that animals also have an imagination and a consciousness, that they create an inner world just like we do, then we’d be forced to deal with animals in a very different way.

Even people who love and respect animals rarely treat them as their peers and instinctively, we tend to think of them as fundamentally different. But what if they’re not? What if their inner world is just as vibrant as ours?

Peña-Guzmán’s When animals dream forces us to grapple with that question. He doesn’t prove it unequivocally; he doesn’t even claim to do so. In fact, his book poses more questions than answers. But as most philosophers do, he makes his case and then asks the reader to ponder and draw their own conclusions.

These questions have never been more important. We’re living through a mass extinction that we ourselves are causing; on top of that, we kill billions of animals every year for consumption. For the vast majority of people, animals are nothing but food, labor, or material. Do we want to treat them as more than that?

Peña-Guzmán doesn’t really focus on that directly, but the implication is clear. A mind that dreams is a conscious mind, a mind that builds and envisions. A mind that dreams can create different worlds and have complex thoughts, and while those thoughts may not be the same as ours, they are no less valuable.