Something interesting about the octopus is that it is independent and learning from the time it is tiny.
It continually learns from the real world, as more and more neurons accumulate.
This layered learning may be an advantage in terms of compact representations.
No doubt, the human fetus brain learns much earlier than birth, or even from emergence of first neurons. But it isn't learning from the environment directly, or making survival critical choices, from first neural emergence.
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Another octopus advantage maybe that it has relatively independent "brains" behind each eye, and along each leg. The distribution of brain in a way that reflects its physical distribution, might offer optimizations too.
We know humans benefit from partially independent spinal cord activity. This is suggestive evidence that the distributed intelligence of an octopus may be an advantage.
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For exhibited intelligence per time, no other creature including humans comes anywhere close. They even learn "theory of mind", i.e. the ability to model other creatures situational awareness, ability to perceive, and likely responses to different situations.
To learn all that, without any mentoring or social examples, in the order of a year, along with their exotic body plan and amazing sensory configurations, would make the octopus a wildly implausible science fiction invention, if we didn't actually happen to have them living successfully in astonishing numbers, and pervasively in essentially all ocean environments.
It may have been enormous luck for us, that they live in an environment where technological progression would be very challenging.
The octopus is a very strong candidate for "smarter than humans", as an individual. If we equalize age, it isn't even a contest. If we normalize for lifespan, but equalize for lack of social mentorship, I expect they win decisively again.
(We often forget how much of our survival and progress is predicated on not being individuals. We have a species intelligence that is much higher than our individual intelligence. Since we as individuals gain so much from what is passed to us, we imagine that we would naturally know countless basic things, that if we actually grew up with people who did not know those things, would be far out of reach. Having people around to teach us things, allowed us evolve to be mentally lazy! Shades of current tool/dependency issues. The octopus has never had a crutch.)
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There is no credible estimate of how many octopus individuals inhabit our oceans. But the number is in the billions at a minimum. Including young, it may be tens of billions or more.
