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Will the Octopus Ever Find Its Way Into a Tidy Evolutionary Tree?

New finds in genetics and neuroscience both shed light and deepen the puzzle of the almost "alien" species

Just why the octopus — a short-lived, solitary, invertebrate exotherm — should seem as intelligent as a monkey has become quite the puzzle in recent years. Typical evolutionary explanations don’t really work. The octopus’s biological inheritance is precisely the type that we don’t associate with intelligence. For one thing, it is much more closely related to clams than to monkeys.

What about the fact that the octopus has nine brains? Well, do nine invertebrate brains add up to more intelligence than one? That’s a question worth asking because it probably wouldn’t work with grasshoppers or worms. That is, both types of life form have brains but it isn’t clear how an installation of nine of them in a single individual would be any smarter than just one.

Gallipoli, Canakkale, Turkey; close up of an octopus eye (Octopus vulgaris Cuvier, 1797). Generative AI

Naturally, the octopus has been singled out for a lot of research attention and a recent genetic find has attracted attention: A detailed genetic analysis found that the common octopus has 2.8 billion base pairs of genes:

To gain a deeper understanding of their biology and evolutionary history, validated data on the composition of their genome is needed, which has been lacking until now. Scientists from the University of Vienna together with an international research team have now been able to close this gap and, in a study, determined impressive figures: 2.8 billion base pairs – organized in 30 chromosomes.

University of Vienna. “New insights into the genetics of the common octopus: Genome at the chromosome level decoded.” ScienceDaily. ScienceDaily, 18 October 2023. The paper is open access.

For comparison, humans have about three billion. Chimpanzees have about the same. Is a large genome a necessary factor in advanced intelligence? It’s too early to be sure but the researchers hope to advance investigations into “more distantly related molluscs such as clams or snails” — species hardly known for intelligence. That might provide a more focused comparison.

Why some researchers have wondered if octopuses are alien species

Some other finds about octopus intelligence in recent years give us some sense of why one researcher wondered if the species had an extraterrestrial origin. As PBS tells it,

The unique nature of octopus intelligence has sparked a rather peculiar debate recently: A group of researchers … has suggested that an octopus’ mind might seem so foreign because it may be alien. The hypothesis, published in 2018, states that octopus evolution may have arisen, in part, because of a retrovirus (a type of RNA virus) delivered to Earth by an asteroid during the Cambrian explosion about 541 million years ago.

A J Fillo, “Thinking is for suckers, but if you’re an octopus, suckers are for thinking, PBS, June 28, 2019 The paper is open access.

Anyway, here are some of the other finds researchers puzzle over:

● Many sources have noted that each arm of an octopus can communicate with other arms, bypassing the brain. But, says behavioral neuroscientist and astrobiologist Dominic Sivitilli (who does not think that octopuses are aliens!), it’s even more complex than that: “There are tens of thousands of both chemical and mechanical receptors in each sucker,” he says. “To put that into perspective, each of your fingertips has a few hundred mechanical receptors.”

The team found that if one of an octopus’ suckers finds something interesting, like food, it triggers a sucker next to it to double check. If that sucker is also interested in the potential treat, it triggers the next one. This creates a cascade of neurons down the arm’s ganglia (nerve cell clusters), encouraging the octopus’ arm to then wrap around the item of interest.

This entire process bypasses the animal’s brain—but the system isn’t perfect. Because the suckers can act independently of the brain there’s not always consensus, Sivitilli explains. “Sometimes, the arm plays tug of war with itself,” he says.

Fillo, PBS, 2019

Such a system of information-gathering seems fundamentally different from that of the intelligent mammals we know. That raises a question. Are comparisons in intelligence between octopuses and, say, mammals even meaningful?

● Another factor that may be linked to high cephalopod intelligence is gene editing:

A team of scientists led by Joshua Rosenthal at the Marine Biological Laboratory and Eli Eisenberg at Tel Aviv University have shown that octopuses and their relatives—the cephalopods—practice a type of genetic alteration called RNA editing that’s very rare in the rest of the animal kingdom. They use it to fine-tune the information encoded by their genes without altering the genes themselves. And they do so extensively, to a far greater degree than any other animal group.

Ed Yong, Octopuses Do Something Really Strange to Their Genes, Atlantic, April 6, 2017

● In February of this year researchers got a look at octopus brain waves and found out, in one reporter’s words, that their brains behave in an “alien” way:

[Tamar] Gutnick and his colleagues were able to pick up clear signals of brain activity, but deciphering these patterns is another story. Some of the brain waves resembled the size and shape of mammalian brain activity, but other pulses from the neurons of octopuses were completely bizarre. These were long-lasting, slow oscillations with large amplitudes, which indicates relatively strong electrical activity. These have not been reported before.

Unfortunately, the researchers were unable to find a strong correlation between this activity and the way the octopuses were behaving. Even when the octopuses were moving around, they could find no obvious changes in signal, despite drastic changes in motion or remaining still.

Troy Farah, “The first observations of octopus brain waves revealed how alien their minds truly are,” Salon, February 28, 2023 The paper requires a subscription.

This is what scientists like to call an “active research area.” It is anyone’s guess whether the octopus will ever find its way into a tidy evolutionary tree. Perhaps it’s not wise to wade in with that goal foremost in mind.

You may also wish to read: Octopus intelligence shakes up Darwin’s tree There does not seem to be a tree of intelligence, which deepens the mystery of intelligence. How does a life form gain the ability to process large amounts of information to make intelligent decisions (perhaps feeling pain as an inevitable outcome)?

Denyse O'Leary

Denyse O'Leary is a freelance journalist based in Victoria, Canada. Specializing in faith and science issues, she is co-author, with neuroscientist Mario Beauregard, of The Spiritual Brain: A Neuroscientist's Case for the Existence of the Soul; and with neurosurgeon Michael Egnor of the forthcoming The Human Soul: What Neuroscience Shows Us about the Brain, the Mind, and the Difference Between the Two (Worthy, 2025). She received her degree in honors English language and literature.

Will the Octopus Ever Find Its Way Into a Tidy Evolutionary Tree?