Greatshells and Gemhearts

[Kav]

So this theory just occurred to me and it appears that it hasn't been discussed before. Obviously the gemheart is an extremely important part of a Greatshell's biology, though we haven't been told so far what exactly it's for. Despite the name, I would imagine that these animals still have regular hearts pumping blood around their bodies and the gemheart serves a different function.

We also know from WOB that these animals are so large that they have to enter into symbiotic relationships with certain spren to survive. What we don't know so far is exactly how this works. My theory is that the gemheart inside the animals works in the same way that the gem in a fabrial does - it contains the spren inside it. The power of this specific spren contained in such a way is what allows it to grow so large. When it dies the spren are released and this is why you only see these Greatshell spren at that point. What I can't decide is whether the spren are contained in this way by choice or are somehow forced by the animals. This theory makes sense to me but let me know what you guys think!

 

[Calderis he/him]

If it works the way fabrials are implied to, the shape of the gemhearts would draw the Spren in naturally.

Alternatively, the physical bond between the material of the gemhearts and the greatshell body could be what draws in the Spren, facilitating the animal/spren bond. I lean towards this explanation, as I doubt a mineral growth within a living creature is going to maintain a consistent shape over the creatures lifespan. 

[The One Who Connects he/him]

1 hour ago, Kav said:

My theory is that the gemheart inside the animals works in the same way that the gem in a Fabrial does - it contains the Spren inside it. The power of this specific Spren contained in such a way is what allows it to grow so large. When it dies the Spren are released and this is why you only see these Greatshell Spren at that point.

Well, we know that gemhearts are an attempt to make things that hold Stormlight indefinitely, so... perhaps you are on the right track with this logic.

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Brandon Sanderson

[Chasmfiends are] an introduction of gemhearts and things like this, and the ability of certain creatures to hold investiture permanently, as Szeth says, rather than it seeping away like it does to humans.

[+Extesian he/him]

Hmmm it appears the bond is voluntary symbiosis, not trapping the spren like a fabrial does. 

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Q: How tall would the average chasmfiend be, and how much would they weigh? On a scale from ant to Godzilla.
 
A: So, they're big. Not godzilla big, but larger than elephant big. On average, they're going to loom over you at about twenty feet high, which is deceptive to their size, as they're longer than tall. And some do get even bigger. Weight, though, is a tricky matter with greatshells on Roshar. The symbiosis with spren is how they get around crushing themselves. (Even on a lower gravity planet like Roshar.)
 
Q: Symbiosis is a two way relationship. The chasmfiends get a huge benefit, the ability to not immediately die. So what do the spren get out of it?
 
A: Yes, the symbiosis is a two-way relationship. You'll find out more in future books, but suffice it to say, the spren DO get something out of the deal. (At least, when it happens naturally.)
 
Q: Are you saying that a chasmfiend and whatever spren it binds with can be forced to bond?
 
A: Not in relation to chasmfiends. Go read up on fabrials. 
 
Q: Fabrials are exactly why I asked this question, I thought there might be a way to, I don't know, shove a spren inside a living greatshell's gemheart or something
 
A:  No, that's not what I was implying.

 

[dendrophobe he/him]

I agree about trapping the spren, but from that quote he does seem to imply that the spren do enter the gemheart.  It is simply voluntary, as opposed to fabrials, where they are forced into gems.