How many times did the brain independently evolve?

It depends what counts as a brain.

Nervous systems themselves probably evolved just once, although it's not completely clear.

It may have been twice.

There's a huge collection of animals that includes us and insects and octopuses and earthworms and almost

everyone who have a nervous system that comes from a single invention of that thing probably

sometime around 600 million years ago or so. Now it may be that there was a second invention of the nervous

system, which, whose descendants we only see today in comb jellies, those little light bulb-like

jellyfish that have beautiful, colorful filaments that glow, really, along their sides. They look like jellyfish, but they're not

ordinary jellyfish. They're quite far from other jellyfish and other animals, it seems. And it's

not impossible that they invented the whole thing, the nervous system, separately for themselves,

and that there were two origins.

Now, that's still a minority view, as I understand it.

And let's just proceed by talking in terms of the invention of the nervous system.

Probably about 600 million years ago, probably in a jellyfish-looking creature, radially organized rather than left-right symmetrical like us,

certainly marine. And that wasn't a brain. Brains themselves come on the scene later.

I mean, as I say, it depends what counts as a brain. Let's talk about a

brain as a, you know, significant concentration of neurons in a sort of head-like or front

region of the animal that has a kind of central centralizing control. I'm not sure even quite,

you know, what the right number is for that.

It would be several times, maybe three, maybe half a dozen,

something like that, again, depending on the boundaries.

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