If all the neurons of a brain would be distributed uniformly in the entire body, keeping the same connectivity, there would be no difference in the behavioral abilities of any animal (except the reaction speed), even if it would not have any recognizable brain.

There are two reasons why all animals with a great number of neurons concentrate them into ganglia, and eventually into a single big brain.

The first is that when moving most of the neurons close together the total length of the interconnections between them becomes much smaller, so a much less quantity of materials is needed to build them.

The second is that the speed of signal transmission on the interconnections between the neurons is quite low, so when the interconnections become shorter, i.e. the nervous system becomes more concentrated, the propagation times decrease and the speed of reaction of the animal increases.

The very low speed of signal transmission is why all animals have the main brain in the head, close to the most important sensors.

For a humanoid robot, the speed of light for signal transmission makes irrelevant where the brain is located. Instead of having the brain in the head, a better position is in the chest, where it can be better protected. So what is seen in many SciFi movies, where humans completely disable some killer robots by cutting or shooting their head, would be unlikely to work against a correctly designed robot.

>I think centralizing learning into a brain is smarter, if you pardon the pun.

even we humans don't really do that entirely. the gestalt of different nervous systems that interconnect between themselves and our brain appear to be responsible for a significant portion of the constellation of traits associated with learning.

Evolution doesn't care what seems smart or efficient; it just cares about what works.

That’s true, but it’s also true that what’s efficient generally works _better_ than what isn’t.

OTOH, a redundant brain is more resilient. These things have been around since well before we decided to have bones (and brains) and that alone proves the worth of this approach.

I doubt we'll ever find a very smart jellyfish, but I hope no box jellyfish decides I am a threat. Or a treat.

It also doesn't care too much about what's better when good enough is sufficient.

That's a good point. But there are throughput considerations at the boundaries to the things that the brain wants to control. It makes most sense to centralize logic, and to delegate specialized control out to subsystems only where those specializations are relevant. Essentially making interfaces for control of appendages into APIs where the finer control logic is hidden from the main orchestrator. Exceptions exist where extra control at high levels is warranted (e.g. digits).

I disagree with you but more importantly, so what if you're right. Are you going to design a proper brain for these jellyfish, or advise them to evolve one? What you say is just so totally non-actionable and uninformative as to be entirely useless.