I would assume the species evolved using a similar biochemistry to humans carbon based etc..and come from a planet with Earth like gravity and climate

What's the smallest size an alien species could be while maintaining the same intelligence level as a human? If this species had a voice, would it most likely be high or low pitched?


closed as too broad by Aify, fi12, James, Frostfyre, Mołot Feb 26 '16 at 11:33

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Welcome to the site Stephanie. This is a tough question for us to answer as there are literally no examples upon which to base an answer. We simply do not know what an alien biology is capable of. That said if you add some constraints to the question, for example that it evolved with a similar biochemistry to humans (carbon based, electrochemical signals, etc) we may be able to get you an answer. If you have questions let us know. Worldbuilding Chat | help center $\endgroup$ – James Feb 26 '16 at 4:03
  • $\begingroup$ Yes I would assume the species evolved using a similar biochemistry to humans carbon based etc.. $\endgroup$ – Stephanie Feb 26 '16 at 4:07
  • $\begingroup$ Good to know, please edit your constraints into your question (people may not read all the comments when reviewing. The more detailed your question's constraints the more detailed an answer we can give you. Welcome again to the site. :) $\endgroup$ – James Feb 26 '16 at 4:09
  • $\begingroup$ I hope you don't mind, I tweaked your question a little bit based off of what you've said (which is not a lot). I think this question has a lot of potential, if you add a few more constraints, or possible your intentions. I don't think I'd close it, but it could improve a little. I do like the question, though. $\endgroup$ – Xandar The Zenon Feb 26 '16 at 5:15
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    $\begingroup$ A good place to start would be with the smallest fully functional human who does not suffer from any detectable mental defect. $\endgroup$ – Sean Boddy Feb 26 '16 at 5:52

These two questions are totally different. The voice one is easy -- if it has a smaller voice box, it will likely have a higher pitched voice due to physics. However it would be trivial to construct a small creature with a large voice box. The vocal tract is a small portion of human from.

Intelligence is a more difficult question, given that we really aren't very good at defining what intelligence is. However, you may enjoy working with the Sentience Quotient (SQ). It was a logarithmic measure of processing rate vs mass. If you can process more data with less mass, you get a higher score. A few interesting data points: * Most plants score a -2 (very little processing per unit mass) * Carniverous plants cluster around +1 (more processing than other plants) * Humans score a +13, and most animals cluster around that * A Cray-1 scores a +9 * IBM Watson scores a +11 or +12

The theoretical limits of SQ are -70, processing 1 bit in the lifetime of the universe, using all the mass in the known universe, and +50, which is a limit by quantum mechanics.

Thus, if you want to shrink the size of a human brain by 10 fold, you need a 10 fold increase in processing per unit mass. SQ is on a log scale, so that means you would need a SQ of 14, one higher than humans. Clearly this suggests that one could get quite small with advanced processors like Josephson Junctions (which score a +23), but if you want to stick to using neurons like you or I have in our head, you can't get much smaller without compromising SQ.

Now as to other approaches to increase intelligence, being more efficient with what you have, that's an open ended question. You could play a lot with that, and maybe even explore the difference between intelligence and wisdom. However, SQ is a decent numeric approach you can play with.

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    $\begingroup$ To be specific then, an SQ23 race, scaled down appropriately, could be about $10^{10}$ times less massive than us. If we presume similar density and proportions to humans, that's about $\sqrt[3]{10^{10}}\approx 2154$ times shorter than us. Average humans seem to be around $1.5\text{ m}$, so the aliens would be about $0.7\text{ mm}$ tall. An SQ50 race could be about $3\times 10^{-17}\text{ m}$ tall, which seems very suspicious given that's like 4% the radius of a proton. $\endgroup$ – MichaelS Feb 26 '16 at 4:18
  • $\begingroup$ @MichaelS When they say upper limit, they mean it =) The upper limit is derived from the minimum amount of energy needed to measure a bit (which derives from plank's constant) and the effective mass caused by that concentration of energy by E=mc2. Such a creature would not have mass like a proton, but rather its mass would all be effective mass from its energy, and it would be as energy efficient as the known laws of physics permit. $\endgroup$ – Cort Ammon Feb 26 '16 at 14:06
  • $\begingroup$ Alternatively, maybe the universe is smarter than we think ;-) $\endgroup$ – Cort Ammon Feb 26 '16 at 14:07
  • $\begingroup$ A mouse or cat sized brain with human intelligence would have an SQ of? I don't understand how to calculate SQ $\endgroup$ – Stephanie Mar 14 '16 at 23:33
  • $\begingroup$ @Stephanie If you wanted a creature that is 1/100th the mass with the same intelligence as a human, you would need a SQ that is 2 higher than ours: +15. This means they can process 100x more per unit mass (SQ is logarithmic, so 10^2 better processing is +2), and have 1/100th the mass $\endgroup$ – Cort Ammon Mar 15 '16 at 1:25

Taking your assumption of a human-like biochemistry and Earth-like conditions:

Brains in Earth biology, from which neural networks are emulated, follow the same model: numerous very simple cells network together to form a vastly more complex structure called the brain. How inherently intelligent a particular brain is depends on a few factors:

  • Number of neurons. Naturally, the more cells you have the better. Teamwork!
  • Configuration. The exact science is beyond me, but how your available neurons are wired up with each other affects the various aspects of intelligence. For example, capacity for forming and interacting with societies, complexity of communications, capacity and length of memory, capacity for creative thinking etc.

The "technical specs" of individual neurons matter much less than the network with respect to the level of intelligence that brain possesses.

Absolute size also matters not. Functionally equivalent brain cells can differ in both size and shape between species.

Also, take note that intelligence isn't a clear cut metric. It consists of various aspects. Whether a certain species is more intelligent than another depends on what aspects the assessor considers to matter.

As such, in order for a different, smaller species to be as intelligent as a human:

  • It should have the same number of neurons, assuming the same brain configuration. This means the body needs to be smaller, or the neurons need to be smaller to have a correspondingly smaller head, or a combination of both.
  • If the number of neurons differ, then any deficits or surplus in any metric of intelligence being measured must be compensated with a change in the brain configuration - quantifiable, but via a non-uniform 3D specification with a nonlinear relationship to performance change.

This is based on my understanding of neural networks and biology in general. I'm not a neurosurgeon.

The range of a species' voice range appears to evolve independently of the brain. It depends on other frequently environmental factors that seems to be independent of physical size. There are animals both smaller and larger than humans which emit sounds outside the human range of hearing at both ends of the spectrum. The species hearing range does evolve alongside its vocal range though, logically.


Question in full at time of answering:

What's the smallest size an alien species could be while maintaining the same intelligence level as a human? If this species had a voice, would it most likely be high or low pitched?

The alien species could be very very small. Even a future Earth may have areas inhabited by computers that are as intelligent as humans and smaller than some modern-day flying insects. To a visitor from another planet or Earth's past, those creatures inhabiting the planet would "just" be the aliens inhabiting that planet. Such creatures could even be carbon-based if we figure out how to use graphene etc. for such purposes. See also this article for more on computing with the same biochemistry as humans & plants.

Such a small creature would have a voice higher than a human's; the minimum frequency (lowest tone) is proportional to the size of the thing which is vibrating to produce the sound. Of course, it is distinctly possible that the aliens might not communicate via pressure waves (sound) or if they do, the waves might not be within the range humans can hear. For example, they could communicate using electromagnetic waves on some part of the radio spectrum (as most of our wirelessly communicating machines do these days).


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