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My question is quite simple and should be relatively easy (for a biologist maybe) to answer. How small can a creature evolve and become sentient? How likely is this and what environmental factors might lead to their evolution?

I recognize that certain cartoons feature extremely intelligent yet extremely small aliens on Earth (Ben 10) and want a race of beings (micro-Dwarves?) even smaller than dwarves on my world to help combat an evil Mage. While my world has magic I don't want the evolution to be impacted in any major way (assume that magic cannot influence evolution).

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    $\begingroup$ So you want some Dwarf Dwarves? $\endgroup$ – Shadow Z. Mar 25 '15 at 17:44
  • $\begingroup$ I thought there might be a similar question out there. $\endgroup$ – JDSweetBeat Mar 25 '15 at 18:30
  • $\begingroup$ I think the second part of this question, about evolution factors for a small intelligent creature, has not yet been covered, though its very possible I just didn't find it. Might be able to change the wording to focus this question more on that. $\endgroup$ – DoubleDouble Mar 25 '15 at 18:39
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I've moved the summary to the top, read the whole thing to see my reasoning (or lack there-of) ;)

How small can a creature evolve and become sentient?
Unknown for sure. I would guess about an inch large at the very smallest. More likely is that it requires brains bird-size or larger (simply based on the intelligence of crows).

How likely is this and what environmental factors might lead to their evolution?
Extremely unlikely. An environment which allows time to think and benefits for doing so.


The smaller the creature is, the smaller their brain is. Eventually, it is debatable whether that clump of neurons can really be considered a brain. Worms have several clumps of neurons at different points in their body. Are these brains? They probably don't give enough room for sentience though.

One thing to possibly consider is that anything with a spine (vertebrates) has what we can call an "actual" brain (no offense, non-vertebrates, I know some of you do too). According to Wikipedia,

The smallest vertebrates (and smallest amphibians) known are Paedophryne amauensis frogs from Papua New Guinea, which range in length from 7.0–8.0 millimetres (0.28–0.31 in), and average 7.7 millimetres (0.30 in).

Another source for frogs with similar size

I would imagine that the smallest brain you could get that is sentient would have to be a bit larger than that, maybe about the difference of brain-to-body ratios between humans and frogs. However, this is just my thoughts - I am no biologist.

It could very well be that certain brain functions require a certain number of neurons to pull it off. This is actually very likely, judging by the number of species in this world and how many we know to be sentient. I don't think the answer to that is actually known, but someone can correct me if I am wrong.


There are a lot of factors, in my opinion, why such a creature is not likely to evolve, but here's three:

Looking at the proportion of known sentient species in existence compared to non-sentient species, statistics are simply not in our favor.

The smaller animals get, the faster they need to be able to respond to danger. This is because their perspective is so small. Imagine if anything within distance of how far we could see on a clear day outside could be within range of hurting us. Generally a brain to allow thinking about options and decisions would only slow you down.

Body heat will be an issue. The smallest mammal is the Etruscan shrew or Bumblebee Bat at just over an inch long. These animals have to eat a lot to have the energy to keep their body heat up. Going smaller than them would likely be fatal if your creature is warm-blooded.

That shouldn't stop you from allowing such creatures. If there was a gap in fast-responding predators or the intelligence to create tools aided escape, allowing a great advantage, then it would be believable that it could happen.

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Brain size does not correlate with intelligence.
Humans are the only known/acknowledged sentient species, but we don't have the biggest brains. We don't even have the biggest brains compared to body mass. And there are animals with smaller brains that are very intelligent, like crows.
Humans are just wired differently. Our brains work in a different way that we choose to label Sentience, and so I don't see why you couldn't have beings with the same wiring in smaller bodies with smaller brains.

Brain science is still not that well understood.

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  • $\begingroup$ Of course brain size correlates with intelligence. The Smithsonian just doesn't know what "correlation" means. $\endgroup$ – BlindKungFuMaster Aug 22 '16 at 11:34
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Well the smallest man (full grown) in the world is 21.5" (54.6cm) tall. Chandra Bahadur Dangi So that gives you a minimum actual to work with.

Now if you are talking 6" fairies, likely they wouldn't be very intelligent, but they might be self aware.

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