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Take the average human and scale them down to be 55 cm in height, or 1.8 feet essentially, with their body parts being as proportional as the average person's are and keeping neuron density and efficiency the same but lower volume due to their size decrease. Think of them as knee height more or less.

What would the intelligence range be of a mammalian humanoid species as small as this? I've handwaved them as having some form of sentience, but what I do not want to handwave is the intellectual capacity their smaller brains would provide and what would otherwise be their capability to learn and apply their knowledge.

Also, what would be their intelligence range if they instead had the neuron density of something like a raven or some other what could be described as intelligent bird?

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  • $\begingroup$ The phrase "intelligence range" has no generally understood meaning. What do you mean by the "intelligence range of a mammalian species"? (Ah, and we already have such small humanoid species here on Earth. They are called monkeys. They are quite smart in their own way.) $\endgroup$
    – AlexP
    Commented Sep 24, 2021 at 11:54
  • $\begingroup$ @AlexP I suppose intelligence range could be an IQ measurement, but without actually having one of them to test that's going to be a hard if not impossible ask. Would it be reasonable to stick them with 'smart enough to be primitive tribes, not smart enough to figure out metalworking without being taught'? $\endgroup$
    – Giffen
    Commented Sep 24, 2021 at 12:20
  • $\begingroup$ And let's not forget crows. Tool making and use (despite fairly poor manipulators), apparently detailed communication between individuals (can pass along human facial recognition), excellent memory. Brains the size of half a walnut, near enough. $\endgroup$
    – Zeiss Ikon
    Commented Sep 24, 2021 at 12:23
  • $\begingroup$ Related Does size limit intelligence? is you're answer not found in there somewhere? $\endgroup$
    – Pelinore
    Commented Sep 24, 2021 at 20:28

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Letting apart the debate on what makes "intelligence" and how we can measure it, the answer to your question is that we don't know.

Bigger brains do not seem to ensure major intelligence, nor smaller brains seem to ensure lower intelligence: compare whales with dolphins, for example, or crows with cows.

Also, staying in the realm of humans, people suffering from proportionate dwarfism, if the underlying syndrome doesn't affect the brain, do not seem to exhibit a lower intelligence and mental development than their normal counterpart.

And don't forget that the environment also affects the manifestation of what we see as intelligence: feral children, despite being physically normal, are far from displaying signs of basic intelligence.

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  • $\begingroup$ "Bigger brains do not seem to ensure major intelligence" that statement needs challenging I feel, bigger in weight no, but bigger in the total number of neurons yes, particularly when it comes to the number of neurons found in the higher thought centres of the brain // elephant brain in numbers / Birds neurons in the forebrain // you may be thinking of older less complete work on the subject? $\endgroup$
    – Pelinore
    Commented Sep 24, 2021 at 22:34
  • $\begingroup$ "bigger in the total number of neurons" & of course as there are limits on how small you can make a neuron, how tightly you can pack them & how many connections you can squeeze in that inevitably imposes physical limitations on how small for how intelligent a brain can be, the limits just aren't anywhere anyone was looking b4 though, & it's also not in the whole brain that they were measuring in the old studies that were confused by the apparent lack of correlation between size & intelligence they found. $\endgroup$
    – Pelinore
    Commented Sep 24, 2021 at 22:44
  • $\begingroup$ "feral children, despite being physically normal, are far from displaying signs of basic intelligence" no, what they are is far from displaying signs of basic education & normal socialisation (which is unsurprising of course), it's rather important not to confuse cultural norms, learning, experience or knowledge with intelligence. $\endgroup$
    – Pelinore
    Commented Sep 24, 2021 at 23:16
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monkey-level to human-level

If everything scales proportionately, then your humanoids will have brains roughly the size of monkeys. Beyond raw size it's both neuron density and brain structure (where those neurons are used) that matter.

Humans have a similar neuron density to monkeys but a very different layout. If they have a human-like brain layout then your humanoids will concentrate more of that brain mass in the forebrain where "higher" functions exist. That would suggest a very smart monkey.

Corvids (crows, ravens, etc.) have a much higher neuron density and also disproportionately concentrate those neurons in the forebrain. I haven’t seen any research on scaling up corvid brains (because how would you get a grant for that?) but I suspect there would be problems associated with heat management. But assuming you can scale a corvid brain to monkey size, I think you could have the potential for full sapience in your humanoids.

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    $\begingroup$ In many ways we could be talking about primordial dwarfism here, brain development issues & a 'somewhat' lower intelligence is generally associated with that (though you'll not find any definitive studies) but they far outstrip a 'smart monkey', go to college, get degrees, speak multiple languages & so on, so (with a small but otherwise human brain) I think we can do better than a smart monkey even without bird style neurons :) there are going to be limits though & the birds techniques may help counter some of those yes. $\endgroup$
    – Pelinore
    Commented Sep 24, 2021 at 21:48
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    $\begingroup$ @Pelinore I agree. I actually went back and forth over how to express that sentence. $\endgroup$
    – legio1
    Commented Sep 24, 2021 at 22:10

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