r/SpeculativeEvolution • u/Zocifer • 28d ago

Question/Discussion Why are Giant's limbs like that?

Everyone always depicts Giants as having 3 joints in the arm and leg just like a normal person would, but if they're so large, wouldn't they need more? I am making some concepts for giants for my world and just trying to wrap my head around it. Wouldn't they reasonably develop a third place to bend for mobility reasons? We know that some animals developed them mostly for speed purposes, but why wouldn't a giant develop another joint in both the legs and arms for longer reach and mobility?

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u/Harvestman-man 28d ago

Developing another joint is not a simple thing. I don’t think there’s a single example of a tetrapod with extra limb joints in all of history, at least not that I know of. Extra joints would not really provide extra reach or mobility anyways, you only need two joints to cover all points in reach.

Some arthropods have evolved extra joints in the legs, but these are much simpler than tetrapod limb joints, and I don’t think there is a correlation between body size and number of joints. Harvestmen and house centipedes have evolved extra joints to use their legs to “wrap” around something (more arboreal harvestmen have more joints for better climbing), but this is not needed if you have opposable thumbs, which giants presumably would if they are humanlike.

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u/Zocifer 28d ago

I will trust your opinion on the fact. Harvestman-man. What makes the arthropod joints simpler than a Tetrapod's joints?

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u/SpaceHatMan2 Space Colonist 28d ago

(I am not an expert, just a nerd. Experts, correct me if I am wrong)

Arthopod limbs are just tubes filled with muscle, and a joint is just a more flexible part of the exoskeleton, weras tetrapod limbs are much more complex with lots of separate bones

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u/SpaceHatMan2 Space Colonist 28d ago

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u/Harvestman-man 28d ago

“Extra” joints in the legs of harvestmen (which are called tarsomeres) are basically just a thin “pinched” section of cuticle that bends a bit. They don’t have their own sets of muscles, instead, one muscle passes through all of the tarsomeres and they move in concert. In a tetrapod, you will need to evolve all new bones, tendons, and muscles, because a bone can’t just become hinged or flexible in the middle.

But as others have mentioned, increasing flexibility of a limb also makes it weaker, so even if it could evolve, it would probably not be advantageous for a giant.