Is it possible to live without killing?

Question

Hooray! Aliens are discovered, the alien community is out there, and we want to join them.

However to join their illustrious organisation, the Galactic Federation, it is a deeply moral group, and the condition is that no member can harm any life at all. They have a 'zero tolerance' policy on harming any life. This includes:

• a member is not allowed to kill animals (even to eat)
• a member is not allowed to kill plants (even to eat)
• a member is not allowed for any life to be extinguished by their existence, or industries that enable their existence at the time are prohibited from killing any life.

Assume that all people on Earth are wanting to join the Galactic Federation and support this change, that we are willing to use any resource and create technology to do so, and past transgressions up to the moment of Acceptance do not affect a members Application for Membership. It is not necessary for the entire of humanity to comply, and membership is individual only.

So the question is: Is it scientifically possible for a future human to exist without killing any life form?

Answer 1

It is inconcievable that any evolved non-autotrophic life form could exist without preying upon and killing other life forms for their sustenance, whether they be sessile or motile (that we call plants and animals respectively)... except possibly for life forms that follow one particular strategy: Parasitism.

Parasites gain a living essentially by stealing energy and resources from another living being without providing a benefit to the parasitised organism. They don't neccesarily kill their host, and it is not in their interest to do so.

So... it would appear that the members of the Galactic Federation are all parasites or autotrophs... wouldn't it?

This is where evolution comes into it.

An autotroph has little evolutionary need to develop intelligence. All of the autotrophs that we know of (i.e. on earth) are non-sentient. They don't even have what we would think of as a nervous system. Their strategy is to be to maximise their energy input and minimise their energy expenditure, and to avoid being eaten by developing passive deterrents - such as toxins or thorns - or to encourage other species to help them reproduce by offering them something edible as a reward. None of this requires any intelligence or even very much reactivity. Why would an autotroph need to develop intelligence? I can't think of a good reason that wouldn't result in something else dying.

A parasite also has little need for intelligence. As long as they are able to find a host and attach themselves, their host can do all the thinking necessary. The less energy that the parasite expends - such as in having a big brain for thinking, which it doesn't really need to do - the better the probability that the host will survive, benefiting both host and parasite... at least until the parasite needs to reproduce, after which, the host may become less important.

Since it is pretty much impossible for a heterotroph to exist without relying upon other organisms - and as L. Dutch said, without an immune system causing the deaths of pathogens, I can only come to three conclusions:

1. The Galactic Federation are trolling us, by demanding that we do something that is not possible, that they are probably not capable of themselves.

OR

2. The Galactic Federation essentially expects us to transition into an intelligence-bootstrapped existence as beings that rely upon generated or collected power for their source of energy... essentially that we transition away from relying upon organic food supplies, and rely upon machines to supply electrical or other power that can somehow transform our waste products back into nutrients and supply inorganic, non-living elements that can be synthesised into nutrients that we require, essentially turning us into cyborgs dependent upon our machines for our own survival.

OR

3. We develop mind uploading technology, and shed the burdens, needs and drawbacks of the flesh entirely, and live in computing substrate powered by non-harmful technologies.

Personally, I'd prefer to believe option 1. They're trolls... and most of us have probably heard the saying, "Don't feed the trolls."

Answer 2

There Is A Simple (Sci-Fi) Solution

We can easily join the Federation, though not as we are now. But all we have to do is develop mind-uploading technology and live as machines on a sterile world. (Presumably not a sterilized Earth, but maybe Mars.) Those humans not willing to abandon the flesh will be be left out, but may have their interests represented by the post-flesh folks.

Alternatively, if we develop an AI sufficiently sophisticated to be permitted to join, we can hope that it will have fond feelings for its creators, and while that's not exactly as good as being members ourselves, it might be something.

If the other members of the Federation are really killing-free (including individual cells in multicellular organisms?!), they have probably already made the transition away from biology, themselves. Or they were AIs from the start, maybe with harsh constraints like 'no killing at all' put in them in attempt to stop them from going rogue.

Answer 3

• a member is not allowed to kill animals (even to eat)
• a member is not allowed to kill plants (even to eat)

to satisfy these two, one would need to turn into a plant, which are notoriously autotrophic.

• a member is not allowed for any life to be extinguished by their existence, or industries that enable their existence at the time are prohibited from killing any life.

This is more difficult, if not impossible:

• a tree branch can snap and fall, killing whoever gets it on its head (even another plant happening to grow where the branch falls)
• plants are known for producing chemicals to repel/arm organisms trying to feed on them
• any immune systems would be causing the death of the pathogens. Even making the beings immunodepressed would require sterilizing their surroundings, which is equally forbidden.

Answer 4

We could relatively easily bypass the eating restrictions by transitioning to a diet consisting of synthetics, fruits, milk, honey and mushrooms - or if we allow for inhumane acts, the carefully excised parts of living beings, or eating the corpses of naturally deceased lifeforms (whose deaths we have not caused directly, just merely intentionally not prevented). The Federation Ambassadors will definitely love the sight of thousands of legless cattle kept alive by surgically attached tubes and millions of newly hatched chicks left to starve until their carcasses can be processed.

Or a loophole might be abused if the interpretation of "industry" allows it - if we can carefully calibrate an ecosystem which generates all our necessary food and readily kills it for us, we only need to collect the leftovers. But doing that on a large enough scale without it becoming an "industry" is a matter better left to the lawyers who can argue away the definition.

The really hard problems start with the microorganisms - we'd have to transition to a completely sterile environment, but that would cause enormous issues when we need to artificially replicate the effects of bacteria in agriculture, animal husbandry, skincare, digestion, and so on. But on the bright side, surgeries will become a lot simpler if no infections are possible.

Answer 5

No, because of definition

There are many reasons why. We can already say the immune system is a harsh threshold. It kills pretty much anything, including your own cells. Apoptosis is another self destruction of cells because of age or simply because it has done its function. Like that we have apparently webbed fingers during our development in the belly, of which the cells terminate themselves.

But it gets much worse. This is mostly active killing. How about killing by not acting? Or taking resources from an environment, causing others to not have enough?

There's bacteria dying on your skin right now, because they do not have access to the resources just beneath your epidermis. There’s creatures, large and small, dying because you ate something. Intelligence is also a huge consumer of energy, requiring a lot of resources to be maintained. All resources you take, arguably inefficiently, that now aren't available to other life.

We can go even further. You have done nothing to prevent one creature from killing another, while you could.

That means that even if your own body isn't killing itself or other things, you are still responsible for some death in some way. There is no non-killer in existence. Existence itself means you have supplanted at least one other life form.

Answer 6

I think this part needs more clarification:

They have a 'zero tolerance' policy on harming any life.

You said:

This includes:

• a member is not allowed to kill animals (even to eat)
• a member is not allowed to kill plants (even to eat)
• a member is not allowed for any life to be extinguished by their existence, or industries that enable their existence at the time are prohibited from killing any life.

But this is not a "zero tolerance policy on harming any life", this is a zero tolerance policy on killing any life. "Harming life" extends way beyond "terminating life", and, as it stands, our very existence causes harm to pathogens in the air when they get trapped in our various mucus secretions. How do they define harm exactly?

But even beyond that, this comment of yours:

I have considered killing harmful bacteria as also forbidden.

Kinda gets in the way of human reproduction. The male side of the human reproductive system depends on millions of cells, which are "alive" as much as bacteria are , dying on their way to the target and there's no way around that as far as I know. And the female side consists of periodically dropping a cell whose only options are "get fertilized" or "die", so whether or not humans partake in reproduction, death happens as a result of our actions.

EDIT: As L.Dutch points out, this point doesn't hold up if your definition of "life" for unicellular organisms hinges on "they can reproduce on their own", as sperm and ovum can't (there are exceptions regarding ovum, but parthenogenesis in humans is nigh impossible) but bacteria can. They actually aren't equally alive, or alive at all, depending on your definition of "life".

Someone else's answer suggested uploading our minds into machines and living on sterile environments from then on, but that would mean leaving our bodies to die, which would also mean causing the death of every micro-organism forming a symbiotic relationship with us, from the bacteria that compose our intestinal flora, to the mites living in our pores; including our immune system and literally every single cell in our bodies. If bacteria are "life", so are neurons and skin cells, even if they were part of a "higher consciousness with conception of self" that no longer inhabits the body.

So no, I don't think it's feasible the way you present it.

Answer 7

No.

Your immune system is constantly killing large quantities of life. You did ask about living in a non-bacterial environment in the comments, but even putting aside the question of if that would be survivable, your own cells get regular killed by your immune system (that is for example how we prevent cancer).

Answer 8

Is it scientifically possible for a future human to exist without killing any life form?

No, it's not possible in a strict sense. Our biology kills without us having to do anything. We could fake it a bit by eating plants without killing the plant. Animals by chopping off a leg and leaving the animal alive etc,. This might be good enough for a political solution, we have enough of those already which are patently crap but tick the right boxes.

But nothing that would stand up to critical and sincere scrutiny.

Answer 9

Is it scientifically possible for a future human to exist without killing any life form?

Without killing? Sure. Maiming is enough for sustenance. E.g. humans can easily go without killing a pig for obtaining ham, you can simply amputate one of its legs, give it prosthesis instead, and call it a day. Of course you need to raise much more pigs then, but you ain't killing them and it is simply an logistics / engineering problem about finding correct sustaining number. You can even try to do it in non-painful and net-beneficial way (e.g. comparing pig happiness over the lifetime compared of such pig living in the wild by itself). Or we can become scavengers (although that is likely to be more repulsive, and probably require reducing overall human population more significantly).

However "no member can HARM any life at all" would be much taller order, especially if you consider single-celled microorganisms as alive (as we humans currently do). It would involve at the very least:

• moving out from Earth to completely sterile world (otherwise, good luck in never stepping on any blade of grass, or ever inhaling a grain of pollen or some air or waterborne microorganism -- even if we were to build 100% effective filters, those filter would harm microorganisms by trapping them). Even then, good luck in making sure you don't accidentally e.g. swallow one of those eyebrow mites in your sleep.

• there is "damned if you do, damned in you don't" factor too - if you stop eating those plans / animals and go for e.g. IV-nutrient-feed, you are going to commit mass-genocide of those microbiota in your body. Even slight changes in diet cause different groups of microbiota to flourish or die out. So Galactic Federation would in fact be ordering such mass-genocides as prerequisites of becoming worthy to join them, which would be kinda hypocritical.

• you would need to completely separate people one from another in almost all circumstances (much better then during COVID-19), otherwise first microorganism which threatens life of one individual would wipe-out complete human civilization, as you're not permitted to allow your body to fight back (as it would be harming that microorganism!)

• how about your own cells? e.g. when macrophage in your body disassembles your own cell (be it old cell, or malfunctioning, or cancerous one which displays many characteristics of life, or independent-microbe one - symbiote or parasite), does it counts as "harming life"? if it does, then the prerequisite for membership is for humans to become immortal first. Unless Galactic Federation grants us those tech first, we cannot achieve it at our tech level.

• even with all that, you'd likely be needing for humans to become machinery on sterile worlds (would they still count as humans then?) or plants (i.e. being able to live off sun energy and non-living materials only). Although even surviving as plants is dubious without those microbiota. At last at our tech level.

---

Possible twists:

• One way I can see this might work is if human diplomacy comes to the rescue there: "nonono, we're not really killing those microorganisms, we're actually reintegrating their constituent parts into a greater whole! So are beneficial to them, even when they case to exist in form in which they used to, as they now exist in improved form!" (hey, Borg were able to rationalize their behavior that way, so it might work for humans too).

• Or, we can pull it back on them: "it is obvious that by not accepting us to the Galactic Federation that you are intentionally harming humans by denying us access to all the benefits of the membership, possibly costing many millions of humans lives due to poverty, lack to advanced tech/medicine etc., thus, by you own definition, you are the ones who are unworthy of being members. So, are we going to ratify the rules to make them more sensible and inclusive, or are you disbanding Galactic Federation by eliminating every member today?".

Answer 10

Yes. Milking, shearing and pooping bacteria.

Now that my weird summary has your attention, allow me to elucidate.

Food: Milk is a blood-like substance secreted by mammary glands. It contains all the necessary nutrients of blood without any of the cells. So dairy products are on the table. However the bacteria inside milk should be extracted first either by centrifuge or some other humane means.

The sugar water from plants like sugarcane, symbiotic myrmecophytes or even flower nectar also does not contain living cells. In addition, since insects like aphids aren't part of the Federation, the sugar water they poop out (called honeydew) could also be harvested. As part of the Federation, I assume humans will also gain access to more viable alien flora & fauna for nourishment.

Materials: Things like hair would also on the table since it's made up of nonliving chitin. So shearing animals for wool would still be acceptable. Ivory would still be an option. Materials that have been shed by creatures by moulting would also be acceptable like discarded reptilian skin or the exoskeletons of arthropods. As part of the Federation, I assume humans would also also gain access to more viable alien flora & fauna for these materials.

Spider silk is perhaps the most exciting of these ethically sourced biomaterials since it has many desirable properties. (Harvesting silk from moth pupa is done by boiling them, so no regular silk I'm afraid...)

Also the remains of animals that died of natural causes would also be acceptable. Bones for example. Just... get a good space-lawyer in case this creates misunderstandings.

Lastly and most challenging: the immune system! I have to admit this one is a real doozy, however, it is not insurmountable. It would require some serious genetic engineering to perfect this but immune cells could be made to swallow pathogens whole without digesting them. Basically reprogramming immune cells to treat foreign organisms not as invaders but as toxins to be expelled. The brimming immune cells would then be made to 'expel' their cargo in the bladder or lower intestine.

Also noteworthy, as Matija Nalis has commented, expelling germs out of your body could kill them. So to avoid this Federation members could wear diapers attached to tiny bioreactors in order to keep the germs alive even after expulsion.

The Galactic Federation thanks you for your attention. [End transmission]

Answer 11

No. Humans are the apex predator of their current planet whose entire system of survival consists of a chain of recycling materials through everything's life cycle. Unless we find ways to live like plants do, on air, water and sunlight, with all our sensory, cognitive, movement and reaction speeds intact.

Answer 12

The alien word is not a perfect translation of "alive" and there is a loophole

If we're not even allowed to kill bacteria, then it sounds impossible, but in a boring way.

Since the aliens already have their no-killing Galactic Federation, it's fair to assume that they draw a line: animals and plants count as "alive", but bacteria don't count. There is a threshold somewhere. Bacteria are below the threshold. Skin cells that are shed from your skin every fourteen days, and dandruff flakes that fall from your head, also do not pass the threshold. Although these cells are alive by our current definition of "life", they are meant to be part of a larger multicellular organism, and hence don't count as alive-on-their-own by the aliens' definition.

Of course, aliens have their own language, and their word which we translated as "alive" really is some nuance between "alive" and "sentient", which includes animals and plants but excludes most bacteria and dying skin cells.

Right now we're not very far from being able to grow meat in laboratories. Heap of meat cells in a testtube that is alive enough for cell multiplication, but that never was an animal. If we could really understand the aliens' definition of "life" and why they draw the line precisely where they do, it's conceivable that we would be able to grow meat and plant in laboratories that would stay just below the threshold for "life" in the aliens' sense.

During the years when humans are trying to perfect this process you could even mention several scandals, where some companies claim they have managed to achieve no-life-meat in the alien sense, everyone start eating their food and joining the Galactic Federation, and after a while it is found out that actually their meat is just above the life theshold, not below, forcing the Galactic Federation to evict all humans (and possibly also aliens who have eaten our food).

Answer 13

If you can't join them, beat them.

The Galactic Federation has a REALLY big flaw it it's basic concept... even bigger than the Immune system issue. Thier absolute prohibition of killing means they have no concept of military doctrine, weapons technology, or antibiotics... and even if they could figure out how to weaponize any of thier technology, they would be ethically prohibited from doing so.

So, if they won't give us a seat at thier table, we can just bring our own... or heck, we could just take the whole damn table. What are they going to do to stop us?

No matter how primitive we humans may be compared to them in all other realms of technology, we are millenia ahead of them in at the art of killing things; so, all we need to do is fly around to all thier planets, bomb them into surrendering, and then we get to steal all of thier advanced technologies and rule over the entire Galactic Federation... ehhm... I mean the Human Empire, ourselves. No more Galactic Federation, no more need to figure out how to stop killing things.

Could they Fight Back?

Military technology is always a bit different than its non-military counterparts. A generator is fundamentally different than a cannon. A nuclear bomb is fundamentally different than a nuclear reactor. And a rocket ship is fundamentally different than a guided missile. A civilization forbidden to kill will have all sorts of missing infrastructure and research that will make militarizing thier tech a long and difficult process. Especially if thier scientists haven't already spent thier whole lives sitting around daydreaming ways to weaponize thier tech like humans do. Trying to figure out something as simple as making a missle will be like modern man trying to figure out Roman Concrete on Damascus Steel. For all of our chemistry and scientific tools, these were still a multi-decade processes because we don't think the way these Ancient civilizations did, and we simply did not know what we did not know.

The transition is made especially hard for a civilization that is committed to doing no harm. Thier entire techstack that they have been working on for countless generations would be full of failsafes designed to prevent either accidental or intentional harm. Let's say they try to take an existing ship and fly it into Earth as some sort of improvised doomsday weapon. The central AI will take over and course correct. So they have to redesign and train a new systems AI that is able to kill... except your standard SDK will recognize that you are making a dangerous AI; so, it won't let you compile forcing your to make your new AI from scratch using old, slow, and mostly forgotten programming techniques.

Oh, but what about the chip-set (or alien equivalent) that ship AIs run on. Those likely have hard-printed fail safes in them to prevent AIs from killing too; so, you'll need to design and manufacture new hardware to run your killer AIs on too. Oh, and don't forget the star-drive has a built in gravity detector that will manually override the AI if the ship gets too close to a planet; so, they have to design a whole new star drive control system too. Oh, and did I mention thier navigation array also has a failsafe that will EMP the AI and shut the reactor down if the AI tries to plot a course that intersects a star or planet.

While this may sound excessive, a good analogue to this would be the the Apollo Missions. After the Apollo I disaster, NASA adopted a thier own engineering doctrine of doing no harm. As a result, by Apollo 11, many systems had 6+ redundancies in place to reduce the risk to life as much as possible; so, with something as dangerous as a ship that could depopulate a whole planet, these aliens will have every backup in place they can imagine to stop themselves from misusing the technology they have as a weapon.

All of this together means that to make a weapon against the humans, they need to design thier new weapons and infrastructure from the ground up having no idea how exactly weapons really work. It would probably take them 10-20 years just to make a basic ballistic missile. Making one that can get past human active defensive that we've been RnDing since the mid 20th century: even longer.

Would they fight back, even if they could?

All of this is a moot point if the aliens don't even choose to fight back. While they may follow the no killing rule, at least some of the member races will have experience with dangerous predators and parasites meaning that maintaining this doctrine will come with the acceptance that sometimes a primitive, less evolved species will come along and kill one of them. So, a necessary part of this doctrine will need to be "Not even for self-preservation". If you allow killing for self-preservation, then humans as a whole would have no problem joining the Galactic Federation as we are now, and the whole question is a non-issue, but if you disallow it, then we primitive humans would just be seen as no different than a particularly dangerous species of wolf.

They would do thier best to avoid us, hide from us, contain us, relocate us, etc., and they could actually be very good at it, but every once in a while, we'll find a way to catch them off guard. But unlike wolves that occasionally steal a lamb: we are stealing ships, lab equipment, blueprints, research notes, and star-charts. Eventually we'll learn enough of thier technology that our non-military tech will all catch up, and our military tech will be far more advanced than anything they could improvise last minute when they realize that they can no longer keep us contained.

Answer 14

Depends on how you define living. Even if we put ourselves in a completely sterile environment that has no contract with even single-cell organisms and place our minds into a digital dream world that keeps the body alive through renewable energy and gives the brain a constant dopamine high, our bodies still work to kill potential cancer cells. Also, I wouldn't consider that living but if you do then the answer is yes

Answer 15

Why join if you can rule?

Take their stuff. Eat them for breakfast if you feel like it. Someone have to teach the dumb tree huggers about survival of the fittest.

While humanity tires to solve the dumb puzzle aliens given them a small but determined faction takes control over the federation and makes the rules irrelevant.

In other wards, the federation in question can not exist. It rewards the members who violate the rules and have no means to punish them.

Frame challenge I guess?

Answer 16

Under a strict definition, no creature remotely similar to any life on earth can even come close.

You said "They have a 'zero tolerance' policy on harming any life.". But for a strict definition of "harm" this is impossible.

Every organism that we are remotely familiar with exudes waste products. Those waste products are often beneficial to certain types of other creatures. But those waste products are almost certain to be toxic to other types of life. Prior to the rise of cyanobacteria, there was a plethora of anaerobic single celled organisms. They were nearly driven to extinction because cyanobacteria excrete oxygen which are toxic to many other types of life.

And even simple, single celled plants compete with each other for space and resources leading to harm to others nearby if only be depleting those resources and that space.

You might point out those particular example is taking the definition of harm so broadly as to be pedantic, and I wouldn't disagree.

But even setting those aside, no multicellular life could possibly avoid harm for a broad definition of harm. Just about all multicellular life needs to defends itself from infection. Even plants have ways to fend off fungi and other diseases that could kill them, and those methods often involve things that kill the fungi. Also, that resource competition becomes more obvious at a multicellular level. Large trees often limit the amount of smaller ground cover around them simply by casting shadows. And trees like the Black Walnut often excrete poisons that seem intended (as much as a tree can intend something) to limit other plant growth around them. Things like this often fall under allelopathy incidentally.

Anything with an immune system is killing other creatures all the time to protect itself.

If redefined as murder, then it could be done.

As mentioned, it is hard for anything with an immune system to avoid actively killing other life forms.

But if the rule was limited only to deliberate killing and perhaps unreasonable harm, then even humans could manage it, although it would likely require a much smaller population of humans.

The obvious thing that we usually need to kill for (other than what our immune system does) is food. But there are ways to get food without killing. Fruits do not require killing the fruit tree. While most vegetable harvesting involves harvesting the whole plant and most grain harvesting effectively destroys the plant in the process, there are already exceptions in the real world and if we began selective breeding with that in mind we could readily increase the number of options.

Answer 17

No, it is impossible

The only way to achieve their standards would be to go for a mind-upload tech path and live in space: probably in matrioshka brains. But then we wouldn't be human anymore...

Not that humanity would attempt to join such an organization in any case. If they are such pacifists we would just take the tech from them... Considering the human nature they would be lucky to survive after we dealt with them.

Answer 18

Genetic Engineering

People already living, who want to join are genetically modified (with the help of carefully designed viruses, a future tech that outperforms CRISPR/Cas9 or something different) to start producing their own chlorophyll, chloroplasts, and everything else needed to become autotroph. After that, people eat ground and take sunbaths for feeding. Future generations should inherit the threat, along with the already human senses and motility.

I'm no expert in plant biology, but I think you might need some handwaving (or a lot of further genetic engineering) in order for that to work, e.g., to get rid of all the captured carbon without developing rigid cell walls.

Answer 19

I found the loophole, that makes this possible, and easily.

"It is not necessary for the entire of humanity to comply, and membership is individual only."

Farmers and hunters, any who kill life, intentionally or otherwise, do not have to join. You cannot pay them to provide food, it must be slavery, or you are guilty of contract killing. As for the Immune System... I hope they don't have a way to check.

There are several questions about the legal implications of hired killing... But few about forcing slaves to do so. I recommend looking at those.

Answer 20

Yes sort of....

The technological singularity

The only way to "live" (very very loose definition of this) is to upload our minds into computers and live in space, nowhere near any form of life.

There is no other choice because existing as a biologically creature will always cause death as our bodies are in a fight to the death situation with the life around us. We're covered in life trying to kill us and our immune system killing it right back. Half the cells in your body aren't even yours.

Only by becoming a program living in space could we avoid killing life.

Answer 21

Many plants can be eaten without killing, for example fruits. If you eat an apple, you do not kill anything. You can even drink milk, because drinking milk does not kill the cow. Note, that is normally forbidden for the more hardline vegans.

Problem happens with the unicellular beings. You have an immunsystem and that kills the bacteria and virus entering you. If it would not happen, you would die. Question is, does that count as killing, and do bacteria count as killable beings.

If yes, my suggestion would be to not enter such a braindamaged Galactic Federation. Life should mean only life with self-conscience, and that Galactic Federation is actually a Galactic Empire masked by hypocrysy, so you want independence.

Answer 22

Super Science!

I think that if you super-scienced up a new GI tract and lungs for humanity you could basically remove the need to eat/excrete. You're adding the need for fuel rods or some such, but that's only once every N years and is entirely artificial. Bonus points if you can mine your new fuel out of some uninhabited rock (Mercury).

So you've got a system that can take in CO2 and produce O2. You funnel that extra C into the new 'digestive' system that is again producing Stuff We Need (sugars, nutrients, proteins, etc etc) from locally available matter.

We might need to replace our skin too, since we shed a non-trivial amount of mass that wouldn't otherwise be recycled. Ditto for hair.

Now all that could be either a biological or technological undertaking, or some combination of the two.

Hmm. So maybe we can overhaul a few other systems while we're at it. Eyes! Those are exposed, and we don't want to lose mass via either sweat (covered during the skin replacement) or tears. And given Sufficently Advanced Technology, we can come up with something much better than human eyes, oops but now we need a better visual cortex to process all that additional information... and we could definitely use better long-term memory, and more short-term memory bins (most people have 5-7).

And now we need to be able to convert someone from Old Human to NuYu (TM)! Shades of Old Man's War by John Scalzi (artificially enhanced new bodies from old people on Earth, consciousness transferred from old body, to coexisting in both briefly, to new body... continuity of consciousness is a big deal).

Letting the old body die is fine so long as it is done before joining galactic civilization. These are individuals joining up, so when they join is individual too. Is there a deadline?

"Easy" way

Or we could all just eat vat-grown meat and bacterial products (cheese, tofu). And fruit. And anything from a plant or animal that died of natural causes? Setting up 'natural causes' sounds really sketchy.