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Because I need a spine that works for massive and small creatures I'm thinking of making a plant-based spine (which has its own DNA). The spine acts kind of like a cucumber, in that when it sucks up more water it becomes sturdier, but when it loses water it becomes soft and malleable. A system of muscles squeezes on the spine to make it lose/gain water, like a sponge.

Because these creatures are humanoids, I figured I could put some form of photosynthetic hair on them, like a root comes up through the neck and sprouts out of the skull, allowing the spine to get all of the light it needs to grow with the organism.

Is this feasable? And, if so, what do you think the hair would looke like? (more like wide flower leaves, pine needles, or perhaps even hair-like?)

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  • $\begingroup$ This rigidness in water-saturated plant tissue is called turgor pressure, and is the result of passive water transport into tissues made from cells with cell walls. $\endgroup$
    – user458
    Jul 7, 2022 at 20:25

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I like this idea. I am mildly confused why you are comparing the spine to a cucumber rather than to existing human structures that firm and lengthen in response to proper stimulus. No matter.

Some animals (notably the sea slug Elysia chlorotica) become photosynthetic following an algal meal. The mechanism is an area of active study.

Perhaps when your creatures need to photosynthesize they ingest algae, sprout hair and capture sunlight.

Green hair is currently en vogue, so even though flat leaves are better designs I'd probably opt for hair.

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  • $\begingroup$ Thanks for the link, it's been helpful in design. Also, algae is an essential part of their diet, so this would make a lot of sense. I appreciate the comment! $\endgroup$
    – Xivote
    Aug 28, 2017 at 0:13
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Does the spine need to have separate DNA? It might be much simpler if these creatures evolved chloroplasts by themselves or by absorbing algae. What I'm saying is that if it's not a hard requirement, don't have the spine be a separate organism. Heck, even humans have ... organs which vary in rigidity based on liquid content. (I'm being as delicate as I can here)

An interesting side-effect of this might be that your creatures only keep their spine rigidity when they need/want it. They might spend half their time being soft and malleable like molluscs. Huge implications for their architecture, if nothing else.

Now moving to the hair ... Check out this page as a reference ( https://www.hunker.com/13428809/what-is-the-difference-between-needle-leaf-and-broad-leaf-trees ). Takeaway is that broadleafs are better photosynthesizers but require more water. Needle-leafs aren't as efficient as sugar production, but are way more efficient w.r.t. water loss. You might want to have both types on your people, depending on their original climate.

Further note ... don't look to photosynthesis to solve everything. It would take an impractical amount of green hair to make a person carbon neutral (ie sugar neutral as well). What it can do is stretch out the time before you starve to death. So maybe this hair evolved in an area with marginal life support, where dearth is common, and even the tiniest edge might allow you to live til the next good season. So these days, maybe the well-fed yeomen look down on those who still rely on hair-support. The most grossly spendthrift wastrels in the big cities even get buzz-cuts to flaunt their wealth!

Whoah, went off on a big tangent there. But you've got two fascinating biological ideas going on there, have fun with them!

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  • $\begingroup$ Wow, I didn't really think of that. This is why I love this forum, so many different ideas. Thanks for the comment! $\endgroup$
    – Xivote
    Aug 28, 2017 at 0:12
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    $\begingroup$ What's wrong with their fictional creatures being symbionts? As you no doubt already know, humans along with all plants and animals, are also symbionts, as they possess mitochondria with their own DNA. $\endgroup$
    – AngelPray
    Aug 28, 2017 at 9:01
  • $\begingroup$ Oh, there's no problem with the spines being symbionts. It's a question of whether it's key part of the story or background that they be so, or if anything which can get similar physical results will do. I was just pointing that out. Symbionts are great, especially if they talk back to you. I can just imagine if these guys' veggie-spines evolved the ability to speak. You could have a hero of these people who is simply -made- of courage, but his spine is a coward. Or is wanted for some crime which only veggie-crimes can commit. Or... ;D $\endgroup$
    – akaioi
    Aug 28, 2017 at 22:20
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Okay, a few years late here. But my idea is essentially: why don't you make the hair solar collectors, instead of complete leaves?

I've done some research on the topic (for different reasons), but the primary problem I see with the idea of hair being a complete leaf is its thickness. Human hair (if that's what you're going for) has a maximum diameter of 200um. Non-human hair can be as thick as 350um, and whiskers can be even thicker. But unless you're planning to give your animal a head full of whisker thick (or thicker) hair (porcupine head, anyone?), I just don't see how you're going to fit the entire photosynthetic and material transport apparatus inside the diameter of a single hair.

So, instead of making them complete leaves, my idea is to make them a sort of solar collector, using pigments that convert sunlight into voltage. If you're looking for plausibility, look no further than the oriental hornet, whose pigmentation is able to trap sunlight to create a voltage difference across its inner and outer layers. So our hypothetical hair will have a conductive core, surrounded by a layer of photon capture pigments enmeshed in structural proteins (which may even aid in light absorption: keratin is an excellent absorber of UV). The benefit of this approach is that it won't require massive structural changes to our hair, as the basic architecture is the same as normal hair, with slightly different materials. The voltage generated hence will be proportional to the length of the hair.

What to do with this generated voltage, you ask? Well, our lovely friends bacteria already have a solution to this conundrum. Microbial electrosynthesis is a form of autotrophy that involves using electricity to reduce carbon dioxide to acetate. Acetate can then be used as a base material for lipid generation, or even gluconeogenesis via the glyoxylate cycle. If bacteria can do it, I see no reason why cells in the hair follicle of our hypothetical animal cannot. This works better when you consider that hair follicles are already encapsulated with blood vessels, which can supply the required carbon dioxide and water while taking away the finished products in our animal.

That's it. Let me know what you think!

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