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One thing that is fairly common amongst nearly every macro-scale living thing on this planet is the brain. The brain controls when creatures breathe, move, talk, etc., but the brains of said living things have one major thing in common: they are all fairly globular in shape.

Now, this got me thinking why isn’t the brain formed into a different shape. To put it more definite, why doesn’t the brain form into a square or a triangle?

There isn’t any real world example of a different shaped brain, so I couldn’t find any disadvantages or advantages to having such a differently shaped brain.

How would a creature evolve a square shaped brain? What advantages or disadvantages would arise from this brain compared to the common globular-shaped brain?

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  • $\begingroup$ Cephalopod brains are tori. That seems like a pretty different shape to me.... $\endgroup$ – Logan R. Kearsley Mar 2 at 1:52
  • $\begingroup$ I just find out that growing into adult our brain volume increased by 20 times, surface area by 30 times thank you wrinkles! More area more contacts more bridges and more blood vessels branches think how shape of trees help photosynthesis ignore xmas tree in cold places. $\endgroup$ – user6760 Mar 2 at 2:14
  • $\begingroup$ Recently, researchers found out that there is a golden ratio in human skull which is a pattern found in nature: (Source: sciencedaily.com/releases/2019/10/191003083252.htm). This might explain, in a bigger picture, how things shape. Other possible and related topic is gravitational biology and how the gravity might affect the evolution of living organisms. $\endgroup$ – 0.. Mar 2 at 2:20
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    $\begingroup$ brains actually come in a wide variety of shapes, but you don't get many perfect geometric shapes in biology. $\endgroup$ – John Mar 2 at 2:31
  • $\begingroup$ While rare, cubes are not completely unheard of in nature. Just ask the Wombat. $\endgroup$ – Andon Mar 2 at 3:14
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Lack of structural integrity

Essentially, the reason that the brain is spherical in nature is because the cavity it grows in is spherical in nature. And the reason for this is simple - brains are important. Break an arm, and you can fix it. Break a brain - not so much. And when it comes to strength, spherical and round objects are inherently more structurally sound than square objects.

In order to have a square brain, you need a square container, which means a square head. And square heads aren't as structurally sound as round heads.

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The Brain is a very fascinating organ. There are many aspects of it we simply do not know. It's shape is one of them.

Perhaps a look at embryonic Brain formation would provide us with clues as to why brains are the way they are. Looking at early cell creation and sequences in our egg cells after conception usually tells us clues about genetic instructions required to layer on top of each other to develop organs into what they are today.

This technique can be used to see that we structurally evolved from fish, with early embryos looking 'tadpole-like' and having tails - to be lost later as genetic instructions evolved later to lose our tails.

enter image description here

The Brain forms in our 3rd week of gestation with 3 main cells forming the forebrain, midbrain, and hindbrain. These are expanded to form the main axis, which slowly grow in size and length. The brain is very early split into hemispheres, although it is worth noting at this stage the Brain appears to be linear in nature, curling up on itself to form the classic Brain shape at 3 months.

enter image description here

From four months, folds in the brain become evident as cells are continuously added. No-one really knows why but there are several theories why these folds are evident in all animals. One theory is that in order for parts of the brain to communicate, increased surface area and internal cell structure is important and need to be closely aligned. Cell formation then follows a folded wrinkled structure as all parts of the brain need to be kept close to the central stem, that supplies blood and enables communication with other organs.

enter image description here

This may be a factor preventing the brain from being 'square' often in nature, as it may interfere with the ability for the parts of the square far from the middle, the corners, from being able to access supply and communication structures at its centre.

We also know that many animals develop protective structures around their brains to protect its delicate cell structure, which is easily damaged by trauma and sudden movement. Squares have weak corners which given any impact would easily dislodge.

So to summarise:

  • Brains are actually formed as linear in early development based on a central stem
  • complexity is added as cells grow to form the major components of brains
  • as time continues they scrunch up into wrinkled spheres, for a yet-unknown reason but likely associated with surface area and accessibility to the stem for supply and communication.
  • brains require protection. Spheres are best as well for this.

So can an organism evolve a square brain? There needs to be a major advantage for this to occur - perhaps it lives underwater in a static environment, such that structural protection is not an issue, and its development creates more rigid stems that develop corners early in gestational formation due to mutation. Rigid external structures could determine advantages of this, or an internal square structure (sensory organ perhaps) that the brain stem must wrap around during development.

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Cubes are rare in nature. It isn’t very energy efficient. Spheres are more resilient, and things that grow tend to accrete material, which means it is easiest to add at minimum distance from core.

If you want a cubic brain, it probably needs a substance that naturally forms cubes to be its primary structural element.

Polonium is the only metal with a cubic crystal form... happens because of its atomic arrangement. https://www.e-education.psu.edu/matse81/node/2131

But there are other substances that form cubes. Carbon can, but only under high pressure. Most notably for this discussion: silicon does quite easily. There are many silicon-based amalgamations that cube, and we know silicon makes a good platform for computation. And silicates, unlike polonium, are common in the environment.

So if you’re going to get a cube brain, use a computing substrate that likes to form cubes anyway. Silicon would be my choice.

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a square brain

Very unlikely. Aside from physical structure considerations (e.g. for an animal with a skull, the corners will be very easy to "concuss" at mechanical shocks to the head), the connectivity between neurons will benefit by the shortest to their necessary connections and shortest distance to the meninges.

In this regard, the neurons in the corner of the cube:

  • don't have as many neighbors to connect to. As such, they are a waste in regards with the "processing power" (they aren't helping...)

  • even more, they "shield" their deeper neighbors from the source of nutrients, making the "food" harder to reach (... they are only making the problem harder)

I don't know, this may explain the behavior of PHB
(no, its not polyhydroxybutyrate)

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