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Is it possible for any organisms in the animal kingdom to have more than one brain?

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    $\begingroup$ Do siamese twins count? $\endgroup$ Commented May 29, 2012 at 14:50
  • $\begingroup$ Would siamese twins count as two organisms? $\endgroup$ Commented May 29, 2012 at 15:54
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    $\begingroup$ "Is it possible" and "does it occur" are different questions. Which one are you interested in? $\endgroup$
    – kmm
    Commented May 29, 2012 at 17:55
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    $\begingroup$ Oh I thought if someone could show me where it occurs, then it would be possible. I am interested in either. $\endgroup$ Commented May 29, 2012 at 19:02

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To some degree the answer depends on your definition of what counts as a brain.

Bilaterally symmetrical organisms tend to have some level of cephalization, which involves the concentration of sensory and inter-neurons at one end of the organism (the head).

This aggregation of neurons at the head is typically more complex than aggregations of neurons elsewhere in the body and so it gets designated as a brain whereas the others are designated as ganglia (if they are outside the central nervous system or nuclei if they are within the central nervous system).

In vertebrates, cephalization is very well developed so the brain is typically much more complex than the ganglia (although the enteric nervous system is pretty awesome, its not the brain). However in many invertebrates, the ganglia at the head of the organism (its brain) is not much more complex than the other ganglia around the body.

For this reason, many invertebrates can survive decapitation (at least for a while) and some like the flat worm, can famously survive and regenerate their head after decapitation.

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  • $\begingroup$ Spot on. Great answer. $\endgroup$
    – AliceD
    Commented Dec 18, 2014 at 10:06
  • $\begingroup$ It may be interesting to add that the octopus has a central brain and eight rather autonomous brains per leg, the legs can do things by themselves that the main brain doesn't know, but they follow its instructions. The octopus is widely considered one of the most intelligent and far developed species, with almost no common dna with humans (it split 600mln years ago) and some consider it therefor the most 'alien' organism known to man. $\endgroup$
    – Abel
    Commented Nov 2, 2017 at 16:01

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