Highly Intelligent: What Octopus and Human Brains Have in Common

Juvenile Octopus

Octopuses have complex “camera” eyes, as seen here in a juvenile animal. Credit: Nir Friedman

Cephalopods like octopuses, squids, and cuttlefish are highly intelligent animals with complex nervous systems. A team of researchers has now shown that their evolution is linked to a dramatic expansion of their microRNA repertoire.

If we go far enough back in evolutionary history, we encounter the last known common ancestor of humans and cephalopods: a primitive wormlike animal with minimal intelligence and simple eyespots. Later, the animal kingdom can be divided into two groups of organisms – those with backbones and those without. While vertebrates, particularly primates and other mammals, went on to develop large and complex brains with diverse cognitive abilities, invertebrates did not. With one exception: the cephalopods.

Scientists have long wondered why such a complex nervous system was only able to develop in these mollusks. Now, an international team led by researchers from the Max Delbrück Center and Dartmouth College in the United States has put forth a possible reason. In a paper published in the journal Science Advances, they explain that octopuses possess a massively expanded repertoire of microRNAs (miRNAs) in their neural tissue – reflecting similar developments that occurred in vertebrates. “So, this is what connects us to the octopus!” says Professor Nikolaus Rajewsky, Scientific Director of the Berlin Institute for Medical Systems Biology of the Max Delbrück Center (MDC-BIMSB), head of the Systems Biology of Gene Regulatory Elements Lab, and the paper’s last author. He explains that this finding probably means miRNAs play a fundamental role in the development of complex brains.

Alien-Like Creatures

Octopuses have both a central brain and a peripheral nervous system – one that is capable of acting independently. Credit: Nir Friedman

In 2019, Rajewsky read a publication about genetic analyses conducted on octopuses. Scientists had discovered that a lot of RNA editing occurs in these cephalopods – meaning they make extensive use of certain enzymes that can recode their RNA. “This got me thinking that octopuses may not only be good at editing, but could have other RNA tricks up their sleeve too,” recalls Rajewsky. And so he began a collaboration with the Stazione Zoologica Anton Dohrn marine research station in Naples, which sent him samples of 18 different tissue types from dead octopuses.

The results of this analyses were surprising: “There was indeed a lot of RNA editing going on, but not in areas that we believe to be of interest,” says Rajewsky. The most interesting discovery was in fact the dramatic expansion of a well-known group of RNA genes, microRNAs. A total of 42 novel miRNA families were found – specifically in neural tissue and mostly in the brain. Given that these genes were conserved during cephalopod evolution, the team concludes they were clearly beneficial to the animals and are therefore functionally important.

Rajewsky has been researching miRNAs for more than 20 years. Instead of being translated into messenger RNAs, which deliver the instructions for protein production in the cell, these genes encode small pieces of RNA that bind to messenger RNA and thus influence protein production. These binding sites were also conserved throughout cephalopod evolution – another indication that these novel miRNAs are of functional importance.

Cephalopods Playing With MicroRNAs

Cephalopods playing with microRNAs (yellow): microRNAs may be linked to the emergence of complex brains in cephalopods. Credit: Grygoriy Zolotarov

New microRNA families

“This is the third-largest expansion of microRNA families in the animal world, and the largest outside of vertebrates,” says lead author Grygoriy Zolotarov, MD, a Ukrainian scientist who interned in Rajewsky’s lab at MDC-BIMSB while finishing medical school in Prague, and later. “To give you an idea of the scale, oysters, which are also mollusks, have acquired just five new microRNA families since the last ancestors they shared with octopuses – while the octopuses have acquired 90!” Oysters, adds Zolotarov, aren’t exactly known for their intelligence.

Rajewsky’s fascination with octopuses began years ago, during an evening visit to the Monterey Bay Aquarium in California. “I saw this creature sitting on the bottom of the tank and we spent several minutes – so I thought – looking at each other.” He says that looking at an octopus is very different to looking at a fish: “It’s not very scientific, but their eyes do exude a sense of intelligence.” Octopuses have similarly complex “camera” eyes to humans.

From an evolutionary perspective, octopuses are unique among invertebrates. They have both a central brain and a peripheral nervous system – one that is capable of acting independently. If an octopus loses a tentacle, the tentacle remains sensitive to touch and can still move. The reason why octopuses are alone in having developed such complex brain functions could lie in the fact that they use their arms very purposefully – as tools to open shells, for instance. Octopuses also show other signs of intelligence: They are very curious and can remember things. They can also recognize people and actually like some more than others. Researchers now believe that they even dream, since they change their color and skin structures while sleeping.

Alien-like creatures

“They say if you want to meet an alien, go diving and make friends with an octopus,” says Rajewsky. He’s now planning to join forces with other octopus researchers to form a European network that will allow greater exchange between the scientists. Although the community is currently small, Rajewsky says that interest in octopuses is growing worldwide, including among behavioral researchers. He says it’s fascinating to analyze a form of intelligence that developed entirely independently of our own. But it’s not easy: “If you do tests with them using small snacks as rewards, they soon lose interest. At least, that’s what my colleagues tell me,” says Rajewsky.

“Since octopuses aren’t typical model organisms, our molecular-biological tools were very limited,” says Zolotarov. “So we don’t yet know exactly which types of cell express the new microRNAs.” Rajewsky’s team is now planning to apply a technique, developed in Rajewsky’s lab, which will make the cells in octopus tissue visible at a molecular level.

Reference: “MicroRNAs are deeply linked to the emergence of the complex octopus brain”25 November 2022, Science Advances.
DOI: 10.1126/sciadv.add9938

5 Comments on "Highly Intelligent: What Octopus and Human Brains Have in Common"

  1. Watch My Octopus Teacher documentary and you can get an idea of the special intelligence these creatures have developed. We loved watching it, even though it has sad parts.

  2. As a 8 yr old I lived next to the Ocean in Niu Valley. I had a dingy and would paddle out over the reef to visit my friend 8, an octopus that I made friends with while taking a break from spear fishing. 8 lived in a deep grotto in the reef and I would take live minnows for 8s snack. I would sit on the edge and 8 would come up and sit next to me wrapping a couple of tentacles around my leg. 8s head was about the size of a softball 🥎 with arms a foot or more. I talked to him or her and 8 would flash color or change color especially if I whistled. I could pick 8 up and look in his eyes and he would look at my face and would tighten his grip on my arm if he liked the experience. We were friends for 2 years and he would come up Ben if a month went by between visits. 8 made me realize that all animals in the ocean and land had their own intelligence. 8 loved crawling into my mask and feeling the rubber straps.

  3. Steve Trustman, what a lovely story. Thank you for sharing.

  4. A couple of years ago I read or watched a story about a small family (of humans) who were vacationing at a coast somewhere. One day, as they walked alongside the water’s edge they noticed a small octopus who had gotten itself stranded on the beach outside the water. The family, speaking softly, gently helped the little octopus back into the water. As they continued their walk alongside the water’s edge the little octopus followed them, swimming at the edge of the water along with them for some time.
    The following day the people again went for a walk along the water’s edge just as they’d done the previous day. They looked to see if the little octopus was nearby and sure enough they spotted him. He swam up, nearly out of the water, so the people stopped. The octopus walked just out of the water, paused, began to seem to sort of uncurl, when suddenly he let go of a small shell he’d been hiding. He dropped the little shell at the people’s feet and then backed away from it and stopped just in the water, seeming to wait. The people realized the little octopus was gifting the shell to them as a show of gratitude and friendship. They picked up the shell and exclaimed joyfully. The octopus then swam away.
    This story fascinated me as well as warmed my heart.

  5. “Cephalopods like octopuses, squids, and cuttlefish are highly intelligent animals with complex nervous systems.”

    It’s pathetic if this “Scientific Director” doesn’t realize it’s also true of fishes.
    “He says that looking at an octopus is very different to looking at a fish: ‘It’s not very scientific, but their eyes do exude a sense of intelligence.’”

    “They are very curious and can remember things. They can also recognize people and actually like some more than others.”
    Fishes can, too! He should read What a Fish Knows

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