I am designing an semi-aquatic sapient species known as the Tetrapi. They have an appearance similar to that octopi, only with 4 tentacles comprised of 3 opposable digits. Unlike octopi, they are air-breathing and show full control of their behavioural responses. They are at a technological level of around Ancient Classical Greece and have devised a colour-changing language by chromatophores and a non-linear writing system of carving. They have a central brain with a size of around 1550cc although neural clumps can be observed at the tentacles.

How can I make the Tetrapus brain smaller than a human's while not sacrificing neural capacity? Would a greater density of neurons even work or would there be frequent misfires? Also, should I scrap the neural clumps or would they prove to be an advantage?

Your task is to find if this change is plausible within natural or artificial selection and why this change would occur in a logical way.

I'm sorry if I'm asking too much. I am a new user and I don't have much experience on this website so please be gentle!

  • 4
    $\begingroup$ An interesting line of reasoning to go down is how do you intend to measure these things? You mention being more efficient at storing and accessing things. Science currently does not know a bound as to how much information can be stored in the human brain. All tests we know how to produce simply don't show a limit. $\endgroup$
    – Cort Ammon
    Jul 6, 2017 at 14:59
  • $\begingroup$ Asking how to make a creature more intelligent, less aggressive, have social cohesion, have behavioral control, and be more efficient at storing & accessing information than a humans is a lot of questions for one post. Perhaps narrow it down to one question. $\endgroup$
    – sphennings
    Jul 6, 2017 at 15:07
  • 1
    $\begingroup$ @sphennings, we're discussing an organism here, not a robot. All these factors may be interlinked in any particular species $\endgroup$
    – Monty Wild
    Jul 6, 2017 at 15:19
  • 6
    $\begingroup$ @MontyWild Behavioral traits like aggression and brain structure aren't closely linked in known animals, though. Bonobos and chimpanzees, for example, have physiologically similar brains, but behave very differently. It would make more sense to ask what type of brain, structurally, would be more efficient, and what environmental factors would lead to the desired behaviors as two questions. $\endgroup$
    – ckersch
    Jul 6, 2017 at 15:34
  • 1
    $\begingroup$ Welcome to worldbuilding stackexchange! Perhaps just a suggestion but, have you ever heard of "Sandbox for proposed questions? Your question is quite broad and would benefit narrowing down or detailings, so I suggest you to post your question here for revision before actually posting it in the main site. Your current reputation would allow you to post on meta as well, as the minimum requirement is 5 rep. Here's the link: worldbuilding.meta.stackexchange.com/questions/4835/… $\endgroup$ Jul 9, 2017 at 19:59

4 Answers 4


As previous posters also has stated there is no direct correlation proven between brain size and intelligence. A possible venue of investigation would be brain wrinkles or folds. (Gyri and sulci) These create a greater surface area in the brain and may be linked to intelligence and greater processing capacity.

Dolphin brain (left) compared to human brain (right)

Please note that the dolphins brain (left) is roughly the same size or and in possession of more gyri and sulci than the human brain (right) and yet the dolphins have not invented fire, thermonuclear war or market economy, but instead just swimmed around eating fish and making wicked back flips. So the case for intelligence may be circumstantial.

An octopus brain looks completely different from a mammal brain. It is more or less completely alien to us. They seem to have a distributed brain with the majority of their neurons actually residing in their arms (which have some semi-autonomous control over movement and their own sense of taste) and a lot of it's processing capacity seems to go towards instinctively controlling a highly complex body.

So what is required for your tetrapi to be smart? Well... actually most likely not much. They are probably already smart (as I recall there is a Question regarding this already on the site, you should check it out if you can find it) and what they lack is social structure (cephalopods being known for being solitary, aggressive, and canibalistic by nature, although there is evidence for them to be surprisingly social as well... so you probably need to talk to an cephalopod specialist, not me). From what I have understood, though, the main case against cephalopod civilization is not their brains nor their smarts but rather physical limitations in terms of life span and gestation. They spawn their young in a fire and forget way and never care for the offspring, which puts limits on social development. Also they die after spawning, making it hard to become a venerable elder and carry on the legends of your people.

Solve those things (moving from water to air will probably do that actually as hatching a litter of a thousand might not be a viable strategy compared to carrying the young internally) and you'll find there actually may be no limit to your cephalopods.

  • $\begingroup$ Exceptional answer! I think they would be egg-laying, having around 5 offspring at a time. They are fertile all-year round and live for a good 40-80 years. I think they would be social creatures and rarely territorial (unless you're talking about stealing the offspring). They have a socialist mindset working for the needs of the many. There is birth control, though, and the tetrapi have figured out how to use IQ tests and birth control to improve the overall intelligence of the race. $\endgroup$
    – Andsaur
    Jul 11, 2017 at 19:56
  • $\begingroup$ Thank you, I'm glad you liked it. Smaller batches of eggs will definitely help with getting the parents to actually parent their offspring. Also I suppose having one parent guarding the nest would help with developing social tendencies as the other parent would be compelled to bring food to it's mate and offspring. $\endgroup$
    – Doomfrost
    Jul 12, 2017 at 7:27

While we don’t fully understand how the human brain actually learns, processes, and stores information we can take a few educated guesses about ways to make it do those things better and faster based on what we do know. The brain appears to function as a large network of neurons with complex thought arising out of the sheer complexity of a network with millions of nodes. In theory, we can increase the “intelligence” of the brain without increasing its size by increasing its speed. If we could somehow increase the rate at which neurons function it would increase the rate at which the brain could process information and make decisions. Neurons form a network by extending long protrusions of their body called axons to make contact with the dendrites of another neuron to form a junction called a synapse. Each neuron receives chemical signals from other neurons’ axons with its dendrites and then can produce an output in the form of an electrical action potential that will travel down its axon to another neuron’s dendrites. In theory if we could accelerate the rate at which this process occurs we could make the neurons faster and therefore the network faster. There are a couple different ways we could go about this like increasing conductivity or axon diameter, ditching action potentials for something even faster like fiber optic cables, etc. There are plenty of ways to build a smaller, faster, and more efficient neuron when starting from scratch. The basic operation of a neuron isn’t all that far from a transistor which we can pack millions of into a silicon chip.

But if you’d prefer to stick with Earth-like neurons and brains there’s one thing we can change that should increase neuron speed across the board. The temperature. The rate at which nearly every molecular biological and chemical process occurs is temperature dependent and generally increases with increasing temperature. This is because temperature at the molecular level is a measure of the average speed of molecules. The higher the temperature the faster molecules are moving. At higher temperatures molecules bump into each other more frequently and with higher energies. Increasing temperature will increase the rate of neurotransmitter release and diffusion in synapses, the speed with which voltage gated channels open and close, and the chemical and electrical conductance of the whole system. Increasing the temperature of a neural network could substantially increase its speed. Of course, we can’t just heat up a human brain because it isn’t designed for that sort of temperature and critical components would break. But an alien that evolved on a much hotter world, or one that had an energy efficient means of heating itself above the ambient temperature of its environment, could have a similar brain to us humans that simply worked much faster.


Increase the surface area of the Tetrapi brain.

Why (Size matters not; surface area does)

The relationship between brain mass and intelligence has been a hot topic in neuroscience and biology for a long time. It derives from a correlation between brain size and body size; however, multiple studies have shown that while body size strongly affects brain size, the brains size does not strongly correlate to higher intelligence. Instead, the primary correlation appears to be brain's surface area. Further neuroscience then showed that the grey matter at the surface of the brain is responsible for thinking. Therefore, higher surface areas increases the brain's processing power.

How can I make the Tetrapus brain smaller than a human's while not sacrificing neural capacity?

Increase the Tetrapi brain's surface area to volume ratio to be greater than humans.


Brain size is not a direct measure of "intelligence" by whatever metric You chose to measure it, otherwise elephants would be much more intelligent than we are (not to speak about whales).

A better, though not very reliable either, criterion is "encephalization factor" which is the size of brain relative to body mass. Rationale behind this is a large part of the brain is used for "normal body maintenance" and only the "excess brain mass" is used for "special functions".

Intelligence is but one of the many functions that are "implemented" is brains; other example is dolphin and bat sonar which accounts for their "abnormally large" brains.

You can have a sentient Tetrapod "just" by reducing its (or should be "his"?) body size to match the reduced brain size (i.e.: preserve encephalization factor).


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .