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Essentially, the organism (Homo Armyus) has 4 arms, 2 placed at the shoulder and 2 at the hips. All bodily functions in Homo Armyus are the same as Homo Sapiens, just the arms are different. Would Homo Armyus have any advantages over Homo Sapiens in an earth-like setting, on planet?

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    $\begingroup$ Isn't this question asking whether monkeys really exist? $\endgroup$
    – AlexP
    Jun 26 at 17:43
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    $\begingroup$ Bujold wrote a book about this; "Falling Free" in her Vorkosigan space opera series. It describes the trials and tribulations of Quaddies shortly after their creation (gene-manipulated). Another later book in the series visits their homeworld. Quaddies were designed to live in null gravity, where hands are much more useful than feet. Recommended, by the way. $\endgroup$
    – RedSonja
    Jun 27 at 6:43
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    $\begingroup$ @AlexP It's asking if The Librarian could exist. $\endgroup$
    – Trish
    Jun 27 at 7:13
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    $\begingroup$ @Trish You realise what you just called The Librarian? $\endgroup$ Jun 27 at 8:10
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    $\begingroup$ @SeanOConnor Dr. Horace Wor... the rest of the word is swallowed in strangling sounds as long red-pelted fingers close around the neck of the speaking person and draw them into the vast spaces of L-Space $\endgroup$
    – Trish
    Jun 27 at 9:30

8 Answers 8

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Arboreal life.

https://www.serengeti-park.de/en/siamang-symphalangus-syndactylus/

siamang

Here is a siamang, one of the "little apes"; this as opposed to the "great apes" which count humans among their number. The siamang has prehensile feet like other arboreal primates. Prehensile feet help with climbing and that would give a genetic fitness advantage. I could imagine in nonarboreal primates where the juvenile must hang on to its mother, prehensile feet would be an advantage to the juveniles. Maybe they would convert to weight bearing less prehensile feet as the juvenile grew bigger and started walking.

I could imagine that in a zero gravity artificial space environment, prehensile feet might again be a help. If the homo species does not need weight bearing feet, extra appendages capable of manipulation might be useful. Phenotypic variables like prehensile feet probably have less effect on genetic fitness for a species capable of space flght.

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    $\begingroup$ Not even necessarily 0 gravity. Martian or lunar gravity would also massively suffice, since even when those hand-footers walk, there is far less weight/pressure on their feet, so less reason to optimize for it, even if they walk a lot during their day $\endgroup$
    – Hobbamok
    Jun 27 at 11:16
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Homo armyus is misnomor.

In truth, Homo Armyus is a member of the family Hominidae, but he doesn't belong to the Homo. He's most likely more closely related to the Pongo than to Homo. In fact, I want to propose that this is actually Pongo sapiens! Let's look at the 1758 depiction of them:

enter image description here

This in turn means, that they will love to work in your libraries as librarians and enforce the rules with iron hands and muscles that can bend steel rods. They also will gather titles such as "DThau & Professor in L-Space Studies".

Because they are better at climbing and stronger, the Pongo sapiens will flock to universities and win in the cutthroat society there while also having access to all the books in the library. Due to their colossal strength compare to Homo sapiens, they drive people out of military positions and fight crime by bending the shackles around the criminals, not simply locking them. They also excel in the thieves' and assassins' guilds, accessing high entries others can't access easily.

Due to their role as gatekeepers in the education sector (There might not be a single Homo sapiens librarian left!), NASA and other high-tech companies might be effectively run by Pongo sapiens, so most space travelers are Pongo sapiens by the necessity of the qualifications anyway.

Their better muscles and climbing arm geometry come also in handy in low gravity: where Homo sapiens need special boots to stay connected to a spot, Pongo sapiens just grab a handrail and have two hands to work, and a third hand to hold the toolkit accessible or move around.

And also, they look rad in orange:

Honorius from Planet of the apes

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Monkey business.

The kind of thing you're describing seems in many ways like a more specialized, less muscular and weirder version of a chimpanzee. Many primates, including many apes, have feet that function much like hands, as their habitat and lifestyle makes it so they're regularly climbing trees and moving around in 3 dimensions among the branches. Because of this, legs and feet that act like a second pair of arms is highly beneficial.

On the other hand, a habitat where there's little to no opportunities to climb and things such as walking and running efficiently is much more important, said apes start to fall behind compared to humans, as we adapted away from a climbing lifestyle and into a lifestyle of traveling long distances bipedally. Your handymen might also be less capable swimmers than humans, though I can't say for sure. The fact that you didn't mention things like muscle mass leaves me something to add: as chimpanzees are more adapted than humans to an arboreal lifestyle, including changes to the spine and pelvis, it's to be expected that your handymen would face heavy competition, especially if their arms are each about as strong as an average human's.

Overall, nature is all about trade-offs, generalization and specialization most of the time. To become the best at something, you must become at least bad or downright terrible at another, especially in activities that demand opposite traits (being a good runner relies on long legs, while being a good burrower requires shorter ones. Being a good climber means you need flexible limbs, while running specializations require less flexible limbs. The list goes on). There's no such thing as a creature that is great at everything, and more often than not you can only get close to being decent at everything, or as they say it, the "jack of all traits, master of none", who often looses at something to the master of one (kinda like Mole crickets, who looked at swimming, burrowing, flying and running and said "all of them, please!").

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  • $\begingroup$ Nature is only about trade-offs because if you dominate another species, that other species tends not to exist much longer. A species, when dominated out of their niche, can flee into another (probably smaller) niche. What survives are specialists; either a generalist who wiped out previous specialists then evolved into new specialists, or specialists who managed to survive being out competed. This doesn't mean there can't be a "better lower limb" that is as good as arms and legs; rather, it means if that if it is found, there might no longer be the other species to compare it with. $\endgroup$
    – Yakk
    Jun 27 at 21:57
  • $\begingroup$ @Yakk the only reason I speak with decent confidence on some limb specificalizing processes such as for running or climbing is because I'm aware that those come from polar opposite pressures: an efficient arboreal creature usually must have flexible limbs because without them it can't move in a 3d environment as well as a specialized version of itself would. Meanwhile running and walking happen on a 2d plain, and so the most efficient limb in this case is an inflexible limb that uses associations of tendons to mitigate the loss of kinetic energy, making the movement more energy efficient. $\endgroup$ Jun 28 at 0:50
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    $\begingroup$ The phrase is actually "jack of all trades, master of none". $\endgroup$
    – Martha
    Jun 28 at 16:51
  • $\begingroup$ @Martha Thanks for the heads-up, I mistyped. $\endgroup$ Jun 28 at 16:58
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I think its simpler to look at this in reverse, what factors make feet more efficient then hands and how can we remove those pro-feet factors to make all-hands more efficient.

Feet are basically hands that require less thought to operate and are specialized for one activity (over hands) walking and running. Where you use the fingers on your hands for all sorts of things, your toes and ankles are designed solely to assist with balance without having to put any thought into what they up to.

To make feet sub-optimal, you thus need an enviroment where it is impossible to walk or run for long distances - which means you may as well have hands instead of feet as they provide more utility. Ergo, you species either lives far above the floor or in an environment which doesn't have a floor (giant chasm ledges ect.).

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    $\begingroup$ Evolutionarily speaking, I think it would be more accurate to say that hands are specialized (generalized?) feet rather than that feet are specialized hands. But I agree that coming at the question from the other side is very useful and identifies the types of environments where an all-hands anatomy would be ideal. $\endgroup$
    – ibonyun
    Jun 27 at 19:11
  • $\begingroup$ @ibonyun Good point. The foot probably predated the hand :p $\endgroup$
    – Alot
    Jun 28 at 8:11
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A healthier back.

The main issue with the upright stance is the load placed on the spine. Quadrupedal animals have an arc-shaped spine which is perfect for that stance. Your "Homo Armyus" has a surprisingly convenient secondary arm placement. Arms closer to the ground remove the need to crouch or bend over to pick something up. This in turn reduces the risk of spinal injuries (a major epidemic in our modern world). Your Homo Armyus probably don't realise how lucky they are to have a pair of arms so close to the ground.

Heads up in battle!

In a hunter gatherer lifestyle, these extra arms allow them to pick up weapons without making themselves vulnerable to a counter-attack. For example, they could use a slingshot and pick up rocks as they shoot. The same is true for spears, arrows or any projectile weapon.

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    $\begingroup$ Many scientists believe that back problems are not inherent to bipedal motion but rather are a side effect of using a spine that was originally optimized for quadrupedal motion. This advantage primarily comes into play if Homo Armyus evolved from a quadrupedal animal in the recent (on an evolutionary scale) past. $\endgroup$
    – Brian
    Jun 27 at 14:12
  • $\begingroup$ It has more to do with keeping a straight back, instead of having to bend over to pick something up. The spine is still vulnerable, but could evolve to be stiffer. But you're completely right. $\endgroup$ Jun 27 at 19:18
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Space Travel

Maybe the species was designed for space travel, i.e. zero gravity, where legs do nothing useful, while more hands can be used for grappling/holding onto walls, equipment etc. Perhaps your species was bred for that purpose, landed on a distant planet and forgot about the technology through generational degeneration?

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To put it simple Homo Armyus would be less mobile on land, but more dexterous and a more efficient worker in fine motor skills. I imagine in an earth-like setting they'd be good swimmers and possibly live by or on lakes. They'd also be good climbers, so alternatively live on trees would also be an option for them.

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Most obviously, dropping legs would cause your poor organism to lose abilities which could not be replaced by arms. (More usefully, why have you not included your own ideas? How far did your imagination take you before something failed and then, what was it that failed?)

Do you not believe that walking upright on legs is the single most obviously important difference between humans and the other apes?

bbc.co.uk/programmes/m000z2cw spent most of an hour this evening explaining both how hard a time Evolution seems to have had in teaching us to walk, and why that matters. Could you watch that?

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