You all probably know what a starfish is. When a starfish is ripped in half, if each half has part of the central disk, then it can regrow into two starfish. Worms can do something similar, if they are cut in half, they regrow into two worms. I was wondering, what is the plausibility of an intelligent starfish developing on an alien planet?

I was thinking the creature could be similar in shape to a human hand. It has some arms it moves around on, which are lower down, then several it uses to manipulate objects, which would be on its sides, and none on top. Its eyes would surround its starfish mouth, in the center of one side of the disk.

Is it possible for this creature be sentient, in the same manner humans are, and still be able to regenerate into two starfish if cut in half?

  • $\begingroup$ What do you mean by "sentient, in the same manner humans are?' Their sentience would absolutely be different from humans, because they're, well, different. Are you asking if they could convince us to treat them as sentient? $\endgroup$
    – Cort Ammon
    Commented Feb 12, 2016 at 19:01
  • $\begingroup$ Yes it is possible. It would need a compact brain though as the larger the brain the more needed to "regenerate". Also they don't regenerate fully they just heal up a bit. $\endgroup$ Commented Feb 12, 2016 at 22:37
  • $\begingroup$ Among the many aliens in Olaf Stapledon's The Star Maker I think there is one starfish shaped species. The Old Ones in At the Mountains of Madness have starfish shaped heads, inspiring the TV Tropes trope called "Starfish Aliens". tvtropes.org/pmwiki/pmwiki.php/Main/StarfishAliens $\endgroup$ Commented Feb 21, 2018 at 4:20
  • $\begingroup$ And there are starfish shaped aliens in Warning from Space (1956). $\endgroup$ Commented Feb 21, 2018 at 4:47
  • $\begingroup$ Correct me if I'm wrong, but I very much doubt that a halved starfish can regenerate into two starfish. For one thing, that'd literally be flawless asexual reproduction, and secondly, it'd destroy vital organs. As far as I know, starfish only regenerate severed arms. $\endgroup$
    – SealBoi
    Commented Mar 17, 2019 at 9:38

4 Answers 4


While Erik and Bowlturner have given good answers, I will suggest that evolution would discourage such abilities.

As the starfish creature ascends to sentience, more and more brainpower is being used to manipulate symbols and concepts, and presumably manipulating appendages at the ends of each arm. A complex visual processing system is also being developed (at the simplest, I would think one eye per segment, but there might be hundreds of tiny eyes scattered across the creature). In an aquatic environment, the senses of taste and smell would also be vitally important, so a good chunk of brain is working on that as well. In addition, the creature might have other senses, for example, the ability to register electrical fields (much like sharks have to sense the presence of potential prey).

When the creature was still a primitive starfish, the sense organs would have become highly developed and lots of brain power devoted to that. Regenerating after being ripped in half made it important that the surviving part(s) could still sense possible predators while regenerating, so the Starfish ability to renew makes sense.

As the creature gets more advanced, the "frontal lobes" (or whatever the equivalent in this being) need to become more and more powerful, and take more and more of the processing power and life support. Being severed by a predatory beast or enemy starfish wielding an obsidian axe is going to be massively disruptive to the higher part of the brain, and while the human and mammalian brains are very plastic, I suspect the limits are not high enough for a full fledged separation.

The regrowing of a lot of higher order brain tissue is not going to be enough, since the surviving half(s) of the creature will also need to learn everything all over again to replace the knowledge and memories lost in the destroyed parts of the brain. The evolutionary disadvantage of devoting so much metabolic process to being prepared to regenerate is probably going to highly disadvantage the beings who retain this compared to the ones who have "streamlined" their metabolisms and nervous systems. They will be simply out-thought by any non regenerating sub species.

Of course, in the very long run, as they become technologically more advanced, they may eventually discover ways to re engage these metabolic pathways via surgery or advanced genetic engineering or stem cells, much like human scientists are working of discovering how we could regenerate limbs.


In theory, maybe. First a starfish would likely be a very different animal should it evolve to have enough brain tissue to become conscious. The brain is an organ, and for a starfish to be able to survive a conscious brain being split apart it already needs to be compartmentalized.

Starfish are radially symetric and this is why they can survive being cut up. They have all the needed functions and organs duplicated. So their brains would also need to have this radial symmetry to have a chance.

It also means that while current star fish are 'identical' when they have finished regrowing, their conscious cousins would be two different beings since they would keep different memories and experiences in their quadrant. Partly because there isn't a real reason for radially duplicating the same memories multiple times. It would be very inefficient use of brain matter for something that you "don't want to happen" namely being split in half.

  • $\begingroup$ You can cut a hologram in half and both halves reconstruct the same image in slightly reduced fidelity. There are coding techniques that have similar properties. There is some weak evidence that our brains have "holographic" memory storage. No reason an alien shouldn't if there is a strong evolutionary pressure to be so. $\endgroup$
    – nigel222
    Commented Feb 12, 2016 at 20:34

I don't see why not, a couple years ago i read of a woman born without cerebellum (that's a big portion) and living a normal life, then there are surgery cases where a large portion is taken off. The brain isn't only characterized by high plasticity but lately it seems that the brain functions are more distributed between the various regions that what was thought. You can bring it to an extreme and make so their brain could have evolved and allowed separation exactly like everything else in the body. The reasons for keeping the memories is to maintain knowledge, so that one individual know all the predecessors knew

  • 2
    $\begingroup$ There is a HUGE difference in the plasticity of the brain when injury occurs early in life and later. Very few people "recover" from massive brain trauma in adult life. Conversely young children can go on to live relatively normal lives, even after having half their brain removed... $\endgroup$
    – Aron
    Commented Oct 28, 2016 at 1:39
  • $\begingroup$ Massive brain trauma means little, massive does not define a quantity in itself and rehab possibilities greatly depend on trauma location. Research has shown that the adult brain isnt as "fossilized" as we thought. Being this the website that it is you can extrapolate from that with a fair bit of wiggle room: think a distributed brain and maintain all the plasticity you prefer for as long in life you prefer... He is making up a creature after all. $\endgroup$ Commented Nov 2, 2016 at 12:23

Several answers have mentioned that keeping a sentient brain in a state where it can be divided in two and still function would take a lot of resources, and that that does not make much sense purely in preparation for a rare event which you are endeavoring to avoid. What if, however, division was part of the creature's life cycle?

Raising a sentient creature to a self sufficient stage of life is a resource hungry process, however you go about it. Humans spend a large proportion of their resources in raising their children, after all.

Here is how such a life-cycle could work:

  • Upon reaching adulthood the creature's brain begins a process of weeding out memories, keeping information and skills that are most useful. At the same time it begins to fatten up, storing resources in it's body. This time would be distressing for the creature due to it's memory loss, but at the same time it might find that key memories become much more vivid.
  • The weeded out memories are then duplicated to separate regions of the brain, and the structures of the brain are duplicated. Long term memory is significantly reduced, as any long term memories are stored twice. Short term memory and other brain function is also slightly reduced, as it is now split between the two brains. The creature might be at risk of split personality disorders at this point.
  • Body and brain divide. Two new young creatures are created with half the adult number of legs, organs, etc., and half the adult brain size. They have the advantage however of an adult level of experience.
  • The offspring re-grow the parts they lack.

A creature adapted for this life-cycle might survive an accidental division and regrow into two new creatures after such a division. However the success of this would very much depend on how close it was reaching to it's natural point of cloning. Early in the process one or both halves would be likely to have greatly reduced chance of survival, and greatly reduced brain function.


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