(2024-11-11) The Silurian Hypothesis It Was The Cephalopods

The Silurian Hypothesis: It was the Cephalopods. Text, footage and photographs by Dr. Klaus M. Stiefel. A hypothesis called “The Silurian hypothesis” wins the title of “most interesting hypothesis most likely to be false” for all of science. In brief, the hypothesis postulates that previously a species different from ours had achieved high intelligence and technological civilization on this planet. The Silurian hypothesis (named after “Silurian” aliens in the brainy British TV series “Doctor Who”) was initially proposed by two astronomers, Gavin A. Schmidt and Adam Frank, as a thought experiment, to see if it would even be feasible to detect the traces of such a hypothetical civilization which had existed many millions of years ago.

They conclude that no ruins of ancient football stadiums, highways or housing projects would survive geological time. In contrast, unusual episodes of global warming and the presence of certain artificial radioisotopes (Plutonium-244 and Curium-247) would give an ancient civilization away. Mass extinctions could be a sign of an ancient smart, technological, fast-expanding species.

besides being an interesting nudge for geological thinking, the question if such an ancient civilization actually happened, and who would have been the species to sustain it is extremely intriguing. The proposition that this was the case, is what I consider the actual most interesting hypothesis most likely to be false, ever, by a wide margin

there is some really well-written science fiction discussing the question, but it hasn’t been tackled in a biologically well-informed way. This is what I’ll try to do here.

While much has been written about hypothetical humanoid descendants of carnivorous dinosaurs as the bearers of the ancient civilization, I believe that it’s the cephalopods – the octopi, cuttlefish and squid- who are the most likely candidates to have reached at least some level of civilization.

Two somewhat different levels of ancient cephalopod civilization are worth considering. The levels are quite distinct in how realistic (or: how more or less extremely unrealistic) they are.

The first level is the Neolithic stage, reached by a species of cephalopod eons ago. Reaching “only” the Neolithic stage could be described as a “Silurian hypothesis light”; it’s not highly significant achievement for a species, and even such a species can significantly turn over the planet’s fauna.

Some of these faunal changes might be detectable millions of years into the future.

Reaching the industrial or space age is much harder than reaching a stage of organized, wide-spread farming.

This level is nothing which can easily imagined following from what’s known about cephalopod behavior, which I will rave about below. This second level is the science fiction of the science fiction; it’s in the heavyweight division of the make-believe, and in this essay, I don’t want to go there.

I came to the conclusion that only the cephalopods are viable candidates for purveyors for an ancient civilization after plenty of reading of the scholarly literature on cephalopods, and also via my personal experience – I scuba dive a lot

As a scuba diver, I observe corals, sponges, sea stars, and most fishes. Squid, cuttlefish and octopi, I interact with. There is a definite two-way component in my encounters with these animals. I look at them, and then I come closer to them. They look back at me, clearly with a theory of mind (my mind), and without any doubt gauging what I intend to do in the next seconds.

These encounters are more like those of tourists from far-flung countries interacting with Austrians in the touristy spots of my home country. The tourists might not completely understand what the Austrians are thinking, when they perform their alpine folk dances, but it’s an encounter eye-to-eye, and neither tourists nor folk dancers doubt that the other side is sentient and conscious.

The scholarly literature is well in sync with my personal observations of cephalopod behavior being outstandingly complex (there is a great monograph with that title by Roger Hanlon and John Messenger). Cephalopods have been called “honorary vertebrates” for their complex nervous systems and sophisticated behaviors.

There is even an octopus named after its tool use, the coconut octopus (Amphioctopus marginatus).

And finally, there is a very sophisticated communication system between cephalopods, based on color and pattern changes in their skins

The skin color changes are used for a variety of purposes, including camouflage and communication with conspecifics

With all of these complex behaviors in place, couldn’t it all have come together sometime, just like it did with humans fifteen thousand years ago, when ecological conditions and human ingenuity came together to spawn the Neolithic revolution. We moved from being very smart creatures who were hunting and gathering in smallish tribal groups to beings involved in organized farming, organized in much larger and more complex groups

Since almost all cephalopods are carnivores, they would have been some kind of pastoralists, raising snails or clams for their consumption. This level of technological achievement is not likely, and certainly not supported by any actual evidence; however, it’s mildly realistic

In contrast, the next level, that of industrialized technology, chemistry, nuclear physics and space travel seems much more unrealistic to achieve by any squid or octopus

A factor which makes reaching this level even more unlikely is that experimental chemistry and physics would be harder to pull off underwater

So why are we not seeing octopus or squid societies today? Fish would eat them. Anyone who observes cephalopods underwater will notice a few striking aspects of their ecology: there are almost always fewer of them around than there are fishes

Consequentially, to understand then when an ancient cephalopod civilization could have happened, we have to look at the evolution of cephalopods, and of that of fishes, and see how they overlap:

The story of cephalopod evolution is an absolutely fascinating chapter in the development of Planet Earth’s fauna. It’s also murky, and some of the fossils supposedly representing the earliest cephalopods are not easy to interpret, even by expert paleontologists who interpret ancient fossils all day.

A crucial window where cephalopod civilization could have occurred is the time between when mentally high-performing cephalopods came to their own, and the time when aquatic vertebrates really took over. Modern (Teleost) fishes exploded, evolutionarily speaking, only in the late Cretaceous, the last of the three ages of the dinosaurs. These are the snappers, groupers, large wrasses and other predatory fishes which keep the octopus numbers on reefs low in this day and age.

Cephalopods got into their evolutionary gears earlier – the number of genera increased substantially, since the beginning of the Triassic, about 55 million years earlier than the diversification of bony fishes. That’s a long time for evolution to push a species over that last hump of intelligence and cooperation needed to attain simple farming civilization. If there ever was an ancient cephalopod civilization, my bet would be that it happened in the Jurassic.

the ancient cephalopod civilization is one of the poetic believes I keep for myself to remind myself of my pre-grad student, sci-fi devouring teenage self

Some papers worth reading if you’d like to dig deeper...