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Really just what the title says. If a human was genetically reengineered (assume super-futuristic-magical level genetic engineering capabilities) for microgravity, what would be some likely changes? The only bounds I have are that they would retain basic human form, I.e. arms, legs, and a head. Would bone structure change at all? Could any improvements be made without compromising the body’s fitness in Earth’s higher gravity?

Edit: Comments have asked for more specifics on what the humans would be doing. A lot of the modifications would be around just living in low gravity without atrophy or decay, if that’s possible; for example, astronauts on the ISS have reported loss of vision and potential harm of radiation while in space. Some stuff would be mobility-based, like being able to move around in low gravity easier or more efficiently, preferably on a rocky or dusty lunar surface. These people frequently move around in EVA suits for the better part of the day, so they won’t always be in a fully pressurized or radiation-sealed environment. As far as what they do, some of them are soldiers, some of them are scientists, and the rest are clergy (think NASA base turned theocratic cult). I guess I’m just asking for ways humans could change in general to survive better on the moon.

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  • $\begingroup$ Look like? Just appearance? What is wrong with 100% the same, no visible changes? What kind of improovement you are looking for - reactive propulsion? Sticky hands? Why do you expect there is an answer to your q with its current form? Isn't an answer just a list of what one would like to have, like that reactive fusion antimater propulsion I mention. $\endgroup$
    – MolbOrg
    Sep 10, 2021 at 2:30
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    $\begingroup$ You could draw inspiration from Lois McMaster Bujold's quaddie race from en.wikipedia.org/wiki/Falling_Free . Among other genetically engineered zero-g adaptations, quaddies were designed to have arms where their legs should be, giving them a total of four arms (hence the name), which made them quite adept at their purpose, being zero-g construction workers. $\endgroup$
    – GrumpyYoungMan
    Sep 10, 2021 at 2:50
  • $\begingroup$ MolbOrg Humans evolved in much higher gravity than I mean in this scenario, so we don’t do well in low-gravity environments. There are plenty of videos of Apollo astronauts struggling even to walk on the moon. My question is if a human could be genetically engineered to fix this, I.e. I would imagine a lower center of mass/shorter legs would help a human keep balanced, or homeostasis could be altered to adapt to lower temperatures and pressures, or resistance to radiation could be improved, etc. Just seeing if people had more ideas $\endgroup$
    – Mark Price
    Sep 10, 2021 at 5:48
  • $\begingroup$ GrumpyYoungMan thanks! Gripping arms/legs do seem useful without much friction. I’ll give that article a look. $\endgroup$
    – Mark Price
    Sep 10, 2021 at 5:50
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    $\begingroup$ But to do what? If they're just going to be sitting doing paperwork at a desk, why any different? If they're engineers, then four hands would be useful, if long-distance couriers, then four long limbs for locomotion might fit. Could you edit to add a few details about the context? Without an edit, it's too broad to answer. $\endgroup$
    – Escaped dental patient.
    Sep 10, 2021 at 12:24

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I guess I’m just asking for ways humans could change in general to survive better on the moon.

Form follow function. Assuming breathable atmosphere from the majority of lifetime spent inside - at least 2/3 of it during active ages, almost all of it during childhood and retirement.

Thinner skeleton, probably longer bones. Weaker muscles - because more of them is a waste. On that note, weaker hearts - no need to fight gravity that much - but about the same volume (the nutrient transport and oxygenation needs is about the same, the brain will have its energy or else).

Gait switched to resemble a kangaroo jumping - more energetically economic that way in lower gravity. Shorter legs, though, with the current leg lengths you lose finer control jumping over distances (overshooting). Probably higher ceiling, to accommodate for this style of walking.

Falling over larger heights isn't that dangerous, so I suspect the architecture will evolve towards higher stair steps. Higher falling distances and longer time spent in free fall (jumping is free fall) will allow more time to get unbalanced or slightly improper attitude at landing. I suspect a set of movements of the cat righting reflex nature will become a muscle-learned habit the toddler will adjust before even walking. In time, those with a more mobile backbone and flexible joins will be at advantage, so expect to see joint flexibility as an evolutionary trait.

Could any improvements be made without compromising the body’s fitness in Earth’s higher gravity?

Nope, Earth gravity will kill them in short time. Their backbone first - better fit for mobility and less for weight, their weaker sinews that keep their organs in place, their brain used to the specific of locomotion in lower gravity causing frequent accidents (with a thinner skeleton in higher gravity). Prepare to have them living in mobile bath tubs while visiting Earth, the water pressure and buoyancy helping them survive.

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If your people live in both environments it would be pretty great to be able to adjust their centre of gravity and maybe even their weight to whatever environment they are currently in, which could be done by an ability to retain water in different areas of the body for example, making them and yourself heavier or lighter depending on the environment. The water storage could also be used in temperature regulation.

Speaking of water, maybe take inspiration from animals living in the oceans, maybe the solution is not (solely) managing to walk properly but controlling the floating around better.

An ability to use suction to hold onto the ground or objects, starfish style, would come handy with both strategies though.

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  • $\begingroup$ I didn’t even think of changing center of gravity, but that sounds really useful, actually. I thought of using a suction (or claws) to hold onto stuff, but figured if the astronaut was going to be wearing a space suit anyways I’d just leave that to the suit itself. Thanks for the answer! $\endgroup$
    – Mark Price
    Sep 10, 2021 at 15:54
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NOTE: below scenario would not require magic. Maybe it can be done easily.. certain cettle breeds have already been bred back to restore ancestor size and strength. I'm not sure about the implications for humans, such as brain size, so let's suppose there is genetic engineering able to do a selective mix of properties..

https://en.wikipedia.org/wiki/Breeding_back

Ape

With advanced generic engineering at hand, consider integrating ape DNA to reconstruct body size, limbs and motoric control as found in bonobo and chimpansee (in case of back-breeding: our common ancestors), featuring gripping feet, with short, jumping legs and relatively long arms. Being able to go forward jumping and grabbing obstacles is what apes do best.

Of course, you'd want to preserve the mental capabilties of the human cortex, the gene swap would need to be partial.. but also in the brain, there are some nice features in apes that would be handy in space. Balance involving center of gravity, a sense for rotation, the accurate muscle control when grabbing.. these ape-properties would come in handy when you move around freely in zero-gravity circumstances.

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    $\begingroup$ Becoming ape-like is cool concept, especially for zero gravity where yanking yourself around is more crucial. I might implement that. Farting to get around would be really funny but I figure an EVA jetpack is probably more efficient lol $\endgroup$
    – Mark Price
    Sep 10, 2021 at 15:51
  • $\begingroup$ jet packs ? you know how much these things cost ? (lol ;) I've removed the farting part.. guess I got downvoted for it ) $\endgroup$
    – Goodies
    Sep 10, 2021 at 16:17
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(assume super-futuristic-magical level genetic engineering capabilities)

Ok, the humans look like whatever they want to look like. Mostly that's a normalish but very attractive human. (Whatever their beauty standards are). But one of the crew would prefer to be a writhing ball of tentacles and that's ok too.

At this stage, the bones degrading from lack of use is just trivially not going to happen. For high G environments there are some restrictions, depending on how high G. You can look human but have greatly enhanced muscles and still have no problem walking around in 10G. But some of the spindlier designs favoured by the low G folks can't work there. Of course, these folks change their genes as easily as their jeans. If they aren't expecting to be in a high G environment today, they might use a body plan that is designed for whatever they are doing in low G. For really high G or other extreme environments, there are specialized body plans, but you wouldn't use them unless you intended to go into those environments.

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Heavy and Robust

It seems like a thin, lightweight form would be useful for these humans, and it would be if not for the fact that humans have to move

As far as my research has found, spacesuits have a mass of around 130kg. This means, factoring in human body mass, that the weight, and therefore normal force, on real moonwalkers' feet is around 320N, which is over 3x the normal force for a regular human on the moon, and much higher than a more gracile species

Why does this matter? Because of friction: Frictional force is the Coefficient of Friction multiplied by the normal force. Hence, a low normal force implies low friction, which is not conducive to getting around

Your humans will need to be at least 200kg in mass to get around, assuming similar grip to spacesuit boots. If they have less grip, they'll need to be heavier to compensate

Most of this extra weight should be concentrated in the torso, as it moves the least. The legs should also have a portion of this weight, both to lower the centre of mass for balance, and to make sure the legs are strong enough to carry the weight comfortably on Earth. The arms would have similar weigh to the legs, as they serve the purpose of balancing the body as the legs move

Apart from that, there are other changes that must be made: Specifically, the excretory parts and the inner ear, alongside other organs that sense weight, will have to be more sensitive in the reduced gravity of the moon. This will mean that on Earth, among other effects, they will relieve themselves 6 times as often as on the moon

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