What if humans had 6 arms?

[Think Ahead]

What if humans had 6 arms? All fully functional (with hands) detailed answers are appropriate. I can't figure out how the shoulder would work. Drawings are do too. Thanks

[Avianmosquito]

There simply isn't enough room for two extra sets of shoulders. One I could see (and they would have to be smaller arms), but not two. In order to make this work, you'd need to make somebody's torso much longer, and that would make them less stable and more prone to back problems.

[PapaQuackers]

https://images4.alphacoders.com/237/237456.jpg

[Afrodactyl]

I would say an extra set of deltoids, lats, pectorals, and trapezius muscles for every extra set of arms. I also imagine the body would have to get exponentially larger the more limbs you had, especially if you want the limbs to be of any kind of real strength.

So something Goliath sized on the lower half and midsection, with human sized (but broader) torso sections stacked on top of one another.

[Eldan]

I don't think it would work. Or at least not fully. THere's no way you could fit three scapulas into a torso, then connect the levator scapulae for all of them. I mean, they'd have to go through the arms higher up.

[Spiryt]

I don't think it would work. Or at least not fully. THere's no way you could fit three scapulas into a torso, then connect the levator scapulae for all of them. I mean, they'd have to go through the arms higher up.

Isn't it levator connected to spine anyway? So there would be 3 pairs of those, connected to spine that can be immobile... They would just have to go somewhere under the muscles of arm above....

Anyway, I would guess that operating 6 arms together with any kind of coordination would require immense brainpower. As in, two times larger cerebellum, or something.

[MikelaC1]

We would all be mariliths

[Bohandas]

There simply isn't enough room for two extra sets of shoulders. One I could see (and they would have to be smaller arms), but not two. In order to make this work, you'd need to make somebody's torso much longer

Or the viscera much smaller

[Admiral Squish]

I think the only way to get 'realistic' six-armed humans would be to basically stack three torsos on top of each other. However, careful design might be able to rearrange organs and string up muscles so that each torso could be significantly shorter than a normal one. I think there would have to be at least one full-sized rib-cage to accommodate the lungs and heart, but the other two could probably be shortened.

I do think there would have to be some increased processing power, brain-wise, but I don't think it'd be significant. Animals coordinate their limbs just fine with small brains. The portion in charge of movement would be proportionally enlarged according to the increase in limbs and muscles it needs to control, but since that only makes up a very small percentage of the brain's total volume, it probably wouldn't be more than 10-15% larger.

[Spiryt]

I do think there would have to be some increased processing power, brain-wise, but I don't think it'd be significant. Animals coordinate their limbs just fine with small brains. The portion in charge of movement would be proportionally enlarged according to the increase in limbs and muscles it needs to control, but since that only makes up a very small percentage of the brain's total volume, it probably wouldn't be more than 10-15% larger.

No animal really can do complex things with their arms like humans do, though. And readily come up with new ways to use it's manipulation capabilities, kinetic abilities to swing, etc.

This would all depend on what would be the point of those 6 arms, I guess.

Rather simple things, like, hanging on/holding on stuff with one pair of arms to comfortably work with the other arms (carve, pick fruits, hack, disarm Death Star, whatever) would require relatively small amount of motor control.

Plenty of apes show that you can just do it with using legs instead though, so what's the point of additional arms?

[TripleD]

Assuming that you could actually get a skeleton and muscle groups working, not much would be different I imagine. Some things would be easier, basically anything that makes you wish "what I would give for a second set of hands!", but there's nothing that would be flat out impossible to do with two that you could do with six.

Musical instruments would definitely be different though.

[Bohandas]

The further addition of a tail might be required to not be frontheavy.

[raygun goth]

Would require multiple stacking shoulders, as previous posters have said.

An interesting thing to note is that we're already at least partially wired for this. Our processing power has the ability to turn a new implement - something that isn't even actually physically attached to our nervous system - into a part of the body. Human neuroplasticity is insane.

How would it happen? Well, we have the limb configuration we do because our ancestors were four-limbed fish called Sarcopterygians (of which five species survive to this day - two are oceanic, and three are freshwater). We've got two arms and two legs - all tetrapods do, which includes reptiles, mammals, dinosaurs, and so on. The gene that controls the way your arms and fingers develop hasn't really changed that much since day one of tetrapodia, and it's called sonic hedgehog, part of the hedgehog series of genes that helps pattern your nervous system, namely the connections to your notochord. Ordinarily it makes four connections. A mutation of the hedgehog series could result a higher number, though most of these results would lead to death or nasty deformity. Let's assume a mutative developmental miracle, though. Replication of the hedgehog series responsible for your arms once or even twice would result in your body attempting to build your shoulders several times. A single duplication might be enough - you could end up with four armed human lineages probably just fine.

As others are saying, a double duplication might be too much. The trunk would be horrifically long and likely severely impair movement and balance.

Not sure how it would impact culture, though.

Assuming that you could actually get a skeleton and muscle groups working, not much would be different I imagine. Some things would be easier, basically anything that makes you wish "what I would give for a second set of hands!", but there's nothing that would be flat out impossible to do with two that you could do with six.

Musical instruments would definitely be different though.

[LudicSavant]

Yup, it's apparently actually called Sonic Hedgehog! https://en.wikipedia.org/wiki/Sonic_hedgehog

Also, a potential inhibitor of the Hedgehog signaling pathway is called 'Robotnikinin.' Because scientists who name stuff are gamers too

[Yabvi]

Four arms could would if we were programmed that way; If we were to have a larger and longer torso then six arms most likely wouldn't be a problem, it's just humans would have needed to evolve for the use of six or four arms, two works better because better coordination and dexterity.