_Other Minds_

24 May 2018

A summary and highlights from Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness, Peter Godfrey-Smith.

The author is an avid diver, and focuses a fair share of the book on descriptions of his amusingly personal interactions with octopuses and cuttlefish.

The 250,000,000th-degree cousin you never knew you had

Wait,” you say, “what’s the difference between cuttlefish and squid, again?” Well, no need to scramble to Wikipedia, Mr. Godfrey-Smith has this covered for us in exquisite detail. It turns out cephalopods have evolved from simple snail-like molluscs that crawled on the seafloor. Over time, they started filling their shells with gas for buoyancy, and eventually started swimming. Once they did, their mollusc foot turned into the charming tentacles we know today, and they developed siphons for swimming.

An early cephalopod after lifting off the floor and growing tentacles.
Image by Smith609 on Wikimedia Commons. Shared under CC-BY-SA.

Faced with evolutionary pressure from fast-developing vertebrates, many cephalopods abandoned their external shells. The only surviving exception is the prehistoric-looking Nautilus. The rest developed into the octopuses, with eight tentacles, and squids and cuttlefish, which have ten. Cuttlefish can be distinguished from squid by the skirt-like fin that surrounds their head. A few evolutionary riddles also come up along the way: for instance, modern jellyfish are generally predatory, but it is unclear what jellyfish ate when they first evolved, as it seems there was nothing of importance in the sea then.

This story is important because, while the last common ancestor of cephalopods and vertebrates (likely a kind of jellyfish) had a nervous system, it was very rudimentary. This means that the emergence of complex cognitive functions in cephalopods happened almost completely independently of that of vertebrates. It gives us reason to believe that cephalopods could think completely differently from us (and also gives us amusing anecdotes: cephalopods’ esophagi go through their brain, so they have to be careful to chew what they eat!)

Shallow-sea llamas

So, just how smart are octopuses? Being social is thought to be a driving factor for the development of complex intelligence in vertebrates, but octopuses aren’t very social and seem to mostly interact when they want to fight.

The real driver behind cephalopod intelligence is most likely the fact that they’ve eschewed the physical protection of a shell, or even bones. They’re mostly soft, squishy, and prone to RUD when they meet a predator’s pointy teeth, so they need to be smart enough to avoid them (while still being able to find prey). Octopuses in particular are curious animals, being some of the few that will actively play with things they’ve determined aren’t food, like Rubik’s cubes. According to the author, a typical interaction with a new octopus can involve some cautious probing from the cephalopod, followed by a gentle attempt at tasting you once they’ve deemed you harmless, and, upon realizing that you’re probably too big to be lunch, showing you around its home.

Although they aren’t very social, octopuses have relatively complex interactions with other individuals: they can recognize other humans and octopuses. When in an aquarium or other research institution, it’s common for octopuses to like some of the humans around them, but not others. Annoyance with a human (or anything else, really) is generally signaled by squirting a fast-and-furious jet of water at the source of irritation (a trait they share with some like-minded chordates).

Pic unrelated.
Image by Johann Dréo on Flickr. Shared under CC-BY-SA.

The smartest specimens can exhibit behavior that looks like pouting when the food they are given isn’t up to their standards. And while cephalopods seem easily annoyed with the repetitive experiments that are often used to quantify animal intelligence, some have things as complex as rapid eye movement sleep.

Physiological relativity

So how does the nervous system that powers all this look like? At a very high level, it’s got about 500 million neurons, or about the same as a dog or 0.5% the number a human has. But look closer and the gap widens: the major areas of a dog’s brain (or even a fish’s or a bird’s) can be put into correspondence with those of a human because they evolved from a similar base, but the cuttlefish’s has a completely different structure.

Indeed, where chordates brain have grown out of an outgrowth at one end of the spine, cephalopod brains have evolved out of the merging of neuron nodules that were placed at some key points of the cephalopod body’s neural network. Brains are still far more distributed in modern cephalopods: each of a squid’s many tentacles has a complex network of neural infrastructure, and seems to be capable of some amount of independent behavior. A severed octopus tentacle can exhibit complex and autonomous movement, including probing and moving, for several minutes before it “dies”.

This probably makes complete sense to them.
From Denis Villeneuve’s Arrival (2016).

One explanation for this could be the extreme range of movement allowed by cephalopod tentacles. Since they have no bone and no inherent structure, they are considerably more complex to control than a vertebrate’s limbs, so they’ve kept a high level of decentralized computing power.

This can be related to recent theories of the evolution of the nervous system. While the mainstream hypothesis has long been that the nervous system evolved to allow the body to react to the environment, the author points out that another key role is coordination: as animals became more complex, they needed to have ways for different parts of their body to synchronize quickly and work together.

Mr. Godfrey-Smith uses these considerations to interrogate some aspects of the mind, like the nature of consciousness and pain. I can’t say I’m completely convinced by the points he makes, which often seem so speculative that it’s unclear what we can really conclude much from them.

Two stories about humans stand out: one about Brother John, a Canadian monk who occasionally lost all speech capacity, internal and external, but was still able to function to some extent during these crises. The other is patient DF, a woman who can no longer consciously see, but is still able to avoid obstacles in a room or place a letter in a slot. These examples both suggest the large computational power of the subconscious parts of our brains.

Memento mori

The book ends on a rather sad note: it turns out that octopuses have a lifespan of about two years. After their use-by date, they’ll start degrading rapidly, losing their sight, delicate color-changing skin, limbs, and, seemingly, their will to live.

An explanation for this short lifespan is that with its soft body, an octopus is likely to get killed by a predator within its first two years. Evolution then tends to select genes that are useful in the first years of life, even if they are detrimental (and possibly lethally so) later in life.

Other random interesting stuff

  • The cover of the book made me discover the book Kunstformen der Natur, available on Wikimedia Commons, which makes for a great screensaver slideshow.
  • The author also mentions the idea of “complex active bodies”, due to Michael Trestman, who points out that out of all the branches (33 animal phyla) that ever developed, only three, chordates, arthropods, and molluscs, are in part or in full capable of movement and complex physical manipulation of their environment.
  • Box Jellyfish seem mean.
  • TVSS: system for the blind where images are turned into pressure patterns on skin. People get the feeling of objects in space, but only if they can control the camera.

September 2018 update

A new study where octopuses were given MDMA suggests that social behavior is mediated by some of the same neurotransmitters (like Serotonin) in invertebrates and in vertebrates. This may be a sign that the two phyla’s neural systems are more closely related—and thus octopuses less alien to us—than thought previously.