How small could humans be and develop a similar civilization?

[DSeid]

Not sure if this is the one but this was a cogent point made by @engineer_comp_geek in a different thread.

Size of Aliens and Space Travel

If you assume that the aliens in question have a somewhat similar biology to us, then the lower limit comes from the brain. Intelligence is basically limited by the number of neurons, and (again, assuming an Earth-like biology, which may or may not be a valid assumption) you can only make neurons so small. Birds, needing to minimize weight in order to fly, have a much higher neuron density than humans. The obvious conclusion from this is that humans are nowhere near the lower size limit. But yo…

And this thread!

Brain size needed for human-type cognition

I’m currently rereading Phillip Pullman’s His Dark Materials trilogy, and in The Amber Spyglass, there’s a species of humanoid beings that are about six or eight inches tall – small enough to ride a hawk, in any case. Since one of my cats was lying on my chest (with his head less than a foot from mine) as I was reading last night, I got to thinking about brain size. Could a creature that small have a brain large enough to handle human speech, do tactical thinking, etc.?