This question is designed to be the successor to Why don't most animals have "heads" in the middle of their bodies?

The previous question was flawed as it fails to accurately define what constitutes a "head".

Keeping on topic, the question here is largely focused on placement of brains and brain-like structures.

Intuitively, common sense would dictate keeping the brain roughly equidistant from everything it controls, decreasing the number of potential failure points between the brain and peripherals.

The standard argument in favor of putting the brain in the head rather than in the middle is for dedicated specialized visual processing. This argument is easily debunked seeing that there's no reason why you couldn't have a brain in the middle of the body and a smaller dedicated optical co-processor in the head. (similar to how a certain premium laptop design 7 years ago had only integrated video built-in but comes with a dock that supplies a high-end external video card). The smaller head-brain would run all of the intensive processing and send a compact representation to the central brain, adding a modest amount of extra reaction time lag. Extra credit if the central brain can partially offload high-level or heavily spatial thought processes to the smaller head-brain (think of it as using a CPU and GPU working together to solve a problem more quickly than the CPU could on its own).


closed as primarily opinion-based by kmm, canadianer, David, user22020, Bryan Krause Oct 4 '17 at 16:04

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Even if having a brain in the middle of the body was better in every way, that doesn't necessitate its evolution. $\endgroup$ – canadianer Oct 4 '17 at 4:07
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    $\begingroup$ The real answer to these "Why?" questions is just "Because". Way back in the pre-Cambrian, our long-ago ancestor developed a body plan with the brain & sensory organs at one end - which IMHO seems pretty sensible for a worm. That ancestor produced lots of descendants, who used variations on that fundamental plan. Didn't have to be that way: a few random choices made differently, and life might be descended from primitive octopus or starfish ancestors, or something entirely different that didn't survive past the Cambrian :-) $\endgroup$ – jamesqf Oct 4 '17 at 5:41
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    $\begingroup$ It's not clear what you mean by "advanced" life form. $\endgroup$ – kmm Oct 4 '17 at 12:55

Because the head is where most of the sensory organs are, and once the brain started developing there it was basically impossible to move it. There is so much relying on its placement, that if it was moved many nerves would no longer be directed to the right place, as there are myoskeletal constraints around it. Basically most of an animals form around the central nervous system and moving major basal organ complexes just doesn't happen in evolution. Moving the brain would be impossible once you got to things like vertebrates.

Smaller CPU only work in systems with lots of redundancy which is not an animal thing. Centralizing processing has it's own advantage because parts of the brain have to communicate with other parts a lot. You would basically have to have almost an entire other brain, which defeats any advantage.

Lastly, there really is not much of an advantage in moving the brain into the chest cavity, as for most animals the brain is small enough to be just as safe in the head as anywhere else.

That said, there are animals with a brain in their midsection; they are called cephalopods.


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