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On my fictitious planet, a 1/2 pound mammal has a brain to body mass ratio similar to that of a human, could they have human-level intelligence, or would the brain be too small to develop that level of intelligence?

Edit: Human intelligence being defined as an high level of problem solving skills, reasoning skills, long term memory, and the ability to recognize one's reflection as a reflection.

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    $\begingroup$ I think that's more suited for biology, and much more complicated than that. First, we don't even have agreed upon definition of intelligence. Second, it's both, and not only, mass and ratio. There are more factors, not all known. So whilst I guess answer would be no, I don't think your question is really answerable without more details. $\endgroup$
    – Mołot
    Feb 15, 2016 at 7:13
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    $\begingroup$ Hmm, I don't see why this was closed. Sure, it might be hard to give a definitive answer. But maybe there's someone on this forum who CAN give a definitive answer. "I don't know" is not the same as "It is unknowable". Even if not, most of the questions on this forum call for speculation and extrapolation. I thought that's what the forum was for. $\endgroup$
    – Jay
    Feb 15, 2016 at 16:42
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    $\begingroup$ A question being on-topic elsewhere does not make it off-topic here. Creature design is clearly on-topic for world building given the OP contains effective parameters. $\endgroup$
    – James
    Feb 15, 2016 at 17:06
  • $\begingroup$ I this the correlation (or lack thereof) of brain size to intelligence is an interesting and useful thing to explore in this forum. $\endgroup$
    – King-Ink
    Feb 15, 2016 at 17:22

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Can we actually know anything about that? As far as I can see, there are only one species with a larger brain-to-mass ratio than humans, the elephant fish.

They are smart but... they lack the opportunity to manipulate their surroundings significantly. After all, they are just fish.

I see you have included:

the ability to recognize ones reflection as a reflection

Image analysis is the sole reason for the large size of their brain, they have evolved to very precisely navigate in the muddy mangrove environment.

Intelligence is complicated, and is not necessarily proportional to brain size nor mass ratio. We also often define intelligence from human-like behaviour, a biased metric that makes us the uncontested overlords of the planet.

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    $\begingroup$ So Long, and Thanks for All the Fish $\endgroup$ Feb 15, 2016 at 8:10
  • $\begingroup$ Surely you mean that is the only living animal you know of with a larger EQ? $\endgroup$
    – Adam Wykes
    Sep 14, 2016 at 20:27
  • $\begingroup$ Elephant fish are also absolutely tiny, brain to body mass is allometric. $\endgroup$
    – John
    Aug 21, 2023 at 18:33
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high level of problem solving skills, reasoning skills, long term memory, and the ability to recognize ones reflection as a reflection is actually found in:

  • dogs and wolves
  • dolphins
  • cats
  • monkeys
  • parrots
  • rats
  • probably more

All can, to some extent, use tools. Communicate. Lie. Trade, in a way. Prostitute. Use mirror to remove sticker from their body, placed in a way they cannot see it. Domesticate other animals (cats domesticated humans, kinda). Only "problem" is - their problems to solve are not the kind of problems we have to solve.

So it's not really about level, it's about kind of intelligence.

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    $\begingroup$ Intelligent dogs certainly sometimes solve problems other than those we usually want them to solve. That's the root of a lot of "difficult" breeds' so-called "problem behaviors". $\endgroup$
    – user
    Feb 15, 2016 at 9:54
  • $\begingroup$ @MichaelKjörling Dogs are hardly a problem when you compare them to rats. Rats' problems are like "how to be where humans don't want us to?", "how to feed on things Humans does not want us to feed on?" and alike. And I think their problem solving beats ours at the moment. $\endgroup$
    – Mołot
    Feb 15, 2016 at 11:26
  • $\begingroup$ Well, I think the problem to be solved here is exactly what we mean by "high level" and "reasoning". Sure, animals routinely solve problems like "how can I get that food from a place that I cannot directly reach". But they don't solve problems like "how can I boost my rep score on Stackexchange". They don't write novels, construct mathematical theorems, mine and smelt metal, or calculate the distance to the nearest star. It can be difficult to define exactly what we mean by "intelligence", but it's blindingly obvious that people have more of it than animals. $\endgroup$
    – Jay
    Feb 15, 2016 at 16:40
  • $\begingroup$ @Jay People go to war. Destroy their environment. Kill for fun. Overpopulate areas they're in. Create tokens like money, and let them take over their psychology. Find cures for civilization diseases they created to begin with. Detonate powerful bombs just to see what would happen, without even planning to use them in real war, ever. It's blindingly obvious we're the stupid ones. $\endgroup$
    – Mołot
    Feb 23, 2016 at 11:52
  • $\begingroup$ @molot Hmm. So animals are also intelligent becfause they too can "use tools", "lie", and "prostitute" ... but people are the real stupid ones because we do these things more and doing these things isn't intelligent at all? Seems to me you just contradicted yourself. In any case, you seem to be confusing "not intelligent" with "evil" $\endgroup$
    – Jay
    Feb 23, 2016 at 14:29
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Corvids in general, and in particular Crows, are fiendishly smart. They recognize faces (though I don't think they recognize their own reflection, but not sure). They pass knowledge on to other crows. They solve multi-step problems without resorting to trial and error. They make and use tools. They are undisputedly some of the most functionally intelligent species on Earth.

This is fascinating because their brains are, quite literally, bird brains. They do not have a particularly high Encephalization Quotient. They do not have very large brains overall, in fact. Their brains are just more special than, say, a small monkey.

Due to the size of animal cells in general having a lower bound, doubtless there is some lower bound to brain size which will end up restricting how small you can get before you just cannot be as intelligent as a human. But if Crows are skirting that line, a half/pound mammal would also be.

And that's just considering the intelligence of the individual. Have you read Vernor Vinge's A Fire Upon the Deep?

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  • $\begingroup$ I always find these bird intelligence statements misleading. There is no doubt they are intelligent for their size of brain. Because if many years of evolution I even believe their brains have matured more than ours. Relatively more connections and mass per m³ inside the brain. They show a few markers of intelligence, but to my knowledge none is able to truly understand and operate in the complexities of even a mundane human life. Smart for their size, definitely. Smart compared to humans? Hardly. $\endgroup$
    – Trioxidane
    Aug 21, 2023 at 18:12
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Humans are primates. We have a pretty standard neuron density and brain to body mass ratio compared to other primates. What stands out is the way our synapses interact and interconnect large regions of the brain. It's more of a software thing.

Our brain waves have a very low frequency relative to what is biologically possible. If your tiny creature had a much faster frequency a few dozen kilohertz as opposed to our few dozen to few hundred hertz then they could process data as fast as we do, and with the appropriate synaptic connections be sapient.

A lot of scifi called intelligent beings sentient. All animals are sentient. They can feel and perceive. Only humans are sapient. Able to think abstract thoughts, have an imagination, have a sense of self, essentially having consciousness.

I adhere to cemi field theory. Basically it states that consciousness isn't just neurons, but also the constructive interference of brainwaves. A lot of brain models see brainwaves as noise while cemi field theory sees them as essential. To the best of my knowledge neither one has definitive evidence yet, but I think cemi field theory is the correct one.

Hope this helps.

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Yes the brain is too small. Neither measure works

Rats have the same brain to body mass ratio as humans. Smaller animals have proprtionally larger brains compared to bodymass. the ratio has to be corrected for total mass to even be helpful. Encephalization quotient (EQ) accounts for this, but there are still several birds with a higher ratio than humans. The measure is really only helpful within mammals which all have similar brain structure but even then it breakdown because some groups have denser brains that is more neuron connections for the same mass. Animals with denser neuron connections show more signals of intelligence than those with the same brain mass but lower density.

to get a brain capable of human level intelligence on a gross scale use Encephalization quotient (EQ) the formula for mammals is

(EQ)= Brain Mass/0.12×(Body Weight)^0.66

Modern humans have an EQ of ~7.6.

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