> > I think there's very little evidence for that. > The evidence is literally every other evolved form of intelligence.

Not really, even harsh environments don't really select for intelligence. Neither does predator-prey dynamics. There are very few significantly intelligent species, and except for octopuses they are all social.

> Do recall "the environment" also includes other intelligent agents an animal needs to compete with.

If you include members of its own species in "the environment" we don't have any thing to discuss, because I fully agree that "the environment" understood as anything external to the individual can trigger the development of intelligence. Because it's trivial to observe that it did.

My claim is more informative (if true), that for the development of intelligence the environment must include populations on individuals living in close proximity, social, interacting a lot, where the strongest evolutionary pressure on a given species is the species itself. That doesn't seem to be true for most octopus species today. As an exception to the rule, their intelligence is interesting. I personally believe it comes from the same source as every other intelligence. And as the living space for octopuses expanded, they became more solitary. Maybe there's something general about this too. That with sufficiently intelligent species (perhaps if the intelligence can't rise anymore due to physical limitations), the other individuals present such a high danger that the species must spread apart and become more solitary. Maybe humans reached this stage already and spread apart, but as they ran out of Earth, they were forced back into old, more social mode, just now on the planetary scale. There is evidence that humans in Europe lived in way smaller groups and used to be way more murderous and cannibalistic not that long ago.

> Basically all octopuses are solitary and die after breeding.

That fits. There's no point in extending the life beyond reproduction if your kids are gona kill you anyways.

> You're proposing that one group of octopuses developed social behavior and multiple breeding, then had a bunch of descendants who went back to exactly the normal octopus behavior.

I'm not proposing that at all. What I'm proposing that all ancestors of octopuses were social and could breed multiple times. However, because of the proximity they became their greatest evolutionary pressure for themselves as they got more intelligent. Eventually they spread out due to some environmental change and their social behaviors and multiple breeding atrophied due to danger from other members of theirs own species, that now could just be nearly completely avoided. And that's the case for nearly all descendant species except this special one for some local environmental reason. This species shows us that social octopuses are (and were) a possibility.

What you consider normal octopus behavior is as normal as eyes of a molerat.

That's a fun story, but it doesn't match the evidence at any point. Your fixation on intraspecific competition as the only significant driver of intelligence is leading you far astray.

The evidence is the lack of any solitary, highly intelligent species apart from octopuses.