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Comment by lawpoop | Hacker News Reader

There was a definition I encountered in high school, which I never found a source for, but seems to be pretty robust and address many of the non-living things other definitions include.

This definition is a rubric of several qualities:

1. Metabolizes energy

2. Stores Information

3. Self-replicates

#1 rules out crystals; they are formed by outside forces, they don't metabolize themselves. It also rules out viruses and prions; they don't ingest any "food" to perform metabolic activity. #2 rules out fire; it doesn't store information in a DNA-like molecule or anything simliar. It's purely a chemical reaction. #3 is the obvious thing that differentiates non-living things like rocks from plants and animals.

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There are still some cool edge-cases. Is a sperm cell alive? An X-chromosome sperm (do X-chromosome sperm have a (probabilistic N)-stage lifecycle?) Are red blood cells alive? Is every molecule of an organism that's alive also considered alive, or just the ensemble? If only the ensemble, are mitochondria alive?

Also, why we consider a single human as living organism, but not a society? Single human without society is a pitiful and helpless chunk of meat, who unable to replicate btw.

Sperm cells can be seen as a haploid phase of many organisms' lifecycle, so are alive by pretty much any definition.

In humans, the haploid phase of the lifecycle is single-celled, while the diploid phase is multicellular. In contrast, in mosses and fungi the haploid phase is multicellular while the diploid phase (sporophytes/zygote) is single-celled.

Red blood cells are discussed in the article.

> Is a sperm cell alive?

The unfertilized eggs of bees become drones, so they must be alive. As a side effect, this indirectly make bee-like insects evolve a lifestyle with a big colony with a queen.

In fungus, most of the life is as haploid (i.e. a single copy of the chromosomes, like sperm and eggs) instead of diploids (i.e. two copies of each chromosomes, like most of our cells.)

In some ¿unicellular organism? [I can't find a good link now] the haploid and diploid versions are almost equal.

[And plants are also weird, some have 4 or 6 copies of the chromosomes instead of 2.]

Self-replication doesn't seem necessary. A human who is infertile is clearly still living. Worker ants who can't reproduce would also be well within the living side of the spectrum to me. I give these examples because it seems to me the definition of living should apply at the individual level, not the species. Individuals after all are the ones doing the dying.

What about cloneability?

The infertile human still came from some fertile being.

replication is still happening in the lower cellular/molecular scales, even when the aggregate organismal level isn't reproducing that pattern. People who take these definitions very seriously aren't implying that elderly people aren't still alive :)

Self replication of information with mutation and evolution would be my definition, which would include viruses, but not crystals, AI could be included if it could evolve on its own.

I think in reality like most things its not black and white, there is a continuum of life and some things are more alive than others.

Edit: perhaps adapting to environment through mutation/evolution or learning or both might be better.

Evolution has led to life but I'm struggling to see why it should be a criterion. What if something happened that stopped humans evolving, and we maintained the same general genetic distribution for the next few millennia? Would we stop living?

Which is why I added the edit. The thing I consider most defining of life is its ability to adapt to its environment both through evolution and later through intelligence and learning.

Yes, without adaptations over time we would probably die as species. I guess that as long as universe is evolving we need to as well to survive.

Simple historic example: change of oxygen level, change of temparature is another likely event

I’d say life is defined by identity (a bunch of information defining a structure), or a self, and the processes that allow this self to stay identical to itself in time. Something like homeostasis at the organism level. #1 and #2 would be utilities to realize this, and not necessarily integrated. Arguably #3 isn’t necessary as others have said and could be seen as only one manifestation among others of the self-preservation process. A trivial illustration of this definition on which we can all agree is death, where self-preservation processes break and identity disintegrates.

Interestingly this definition would encompass countries and probably any social group as long as they have a name, an identity and processes to maintain it. I think life doesn’t need integrated intelligence to be life, though intelligence could probably be defined as a predictive kind of self-preservation process. Essentially devising a chain of actions for moving from state A to state B with a limited set of possible operations and minimized energy consumption. An efficient way to return to initial state, or to another state that increases likelyhood of identity preservation.

As someone else said in a comment, life may be seen as a continuum where these characteristics are more or less developed and integrated, for instance making coutries or viruses living organisms while still distinguishing the unique character of humans or animals.

As is typical for them, viruses are debatable under this definition (and how about computer viruses?)

I would definitely say biological viruses are a life form. They use as a substrate. However, you need the ability to mutate in order to evolve. Computer viruses can't do that at the moment, they are dumb machines/tools that just keep doing the same thing over and over until we wipe them out.

IMO, self-replication is the most fundamental characteristic, and the ability to mutate/evolve is key as well. The rest is all details.

The "metabolism" requirement is an important one, though. If you remove it, and you allow for "self-replication" that's entirely dependent on an external agent, then it seems like you would have to consider all kinds of things as "alive" that would fall outside any common-sense definition of the term. For example, works of literature.

It seems to me literature doesn't self-replicate, we replicate it... And apart from the bible and such, literature usually dies out fairly quickly in the grand scheme of things.

So if humans stopped mutating/evolving (due to gene therapy or some drug), we would stop being life?

Many species “stopped being life” because they took a wrong turn at evolution crossroads. But that may become irrelevant for us in few centuries.

I agree with the other responder. However, humans stopping evolving seems unlikely to happen. For instance, right now, we have birth control. Birth rates are declining rapidly. I don't think that's going to continue. We are in the process of selecting for people who have more children. Nature will find a way to evolve around birth control.

Both you and the other responder just completely ignored my question though. I'm not asking if humans will stop evolving or if other species have gone extinct. I'm saying that if we somehow used CRISPR to stop genetic mutation (let's assume it's possible), but in every other way remained the same, are you saying we would no longer be life?

I'm asking this question because the aforementioned definition of "life" is flawed in my opinion. Evolution has nothing to do with it.

Two things:

1. Unless you have some way to stop time, it is impossible to stop humans from mutating/evolving.

2. I would argue it is part of being human, and being alive, to evolve and adapt to your environment. Humans have multiple ways of doing this. Beyond our ability to genetically evolve, our intelligence is a mechanism we use to adapt to your environment much faster than genetics permit.

Viruses rely entirely on the host cell's proteins for all of their replication. They don't metabolize anything themselves, nor do they create their own copies of themselves. The host cell creates copies of the virus.

Perhaps exploiting an entropy gradient would be more accurate.

"(and how about computer viruses?)"

They don't metabolize energy.

Until you turn on the computer and receive electricity bill?

> viruses are debatable under this definition

I think it's a thin pro-argument. Viruses are completely dependant on the host cell and the host cell's metabolism. The host cell's protein unwraps the jacket, and the host cells' proteins replicate the viral DNA/RNA payload. The virus does not reproduce itself, and it does not metabolize anything. There are no inputs to a virus.

Whereas living cells, give them the proper inputs, and they metabolize energy, catalyze reactions, and create copies of themselves.

You might be interested in the little-known Chemoton model: http://web.archive.org/web/20210221212235/https://www.nation...

    1. metabolic cycle
    2. ~~stores information~~
    2. membrane/boundary
    3. template replication

More recent origin of life theories (even proto-cellular) focus on:

    1. periodicity/cycles
    2. compartmentalization/boundaries
    3. microdiversity/entropy

https://sci-hub.st/10.1016/j.cocis.2007.08.008

Life is self-replicating energy states. As thus, i would include stable energy phenomena.A https://en.wikipedia.org/wiki/Extraterrestrial_vortex could fulfill the requirements for life if it was able to manipulate its environment into producing a re-occurrence aka offspring. So self-replication, aka storing the instructions for re-occurrence into the environment system, is kind of in a flux in extreme cases.

#3 removes the whole class of AI based life forms that would not need to replicate. Our future AI citizens may not appreciate not being thought of as living.

That seems to me a form of begging the question: you assume "AI based life forms" will indeed be life forms, then argue the definition from the parent post fails to account for this new life form.

But that such a thing as AI life forms will exist and be accepted as such by scientific consensus is not a given, at all.

Not really. There is no objectively true unarguable definition of life. When in silico life becomes reality and humans do their human thing of devaluing anything that's not like them, it won't matter what human consensus deems as life. I'm not worried about determining what "indeed will be life forms" no more than I worry about objectively defining what is a good meal or which is the most beautiful color. Humans have no standing it determining what true life is. What's important is developing an intentional stance towards whatever is not us.

The human mind invented the concept of life. There’s no objective definition other than what people decide that it means, because no other form of intelligence tries to make the distinction.

I’m pretty sure siliconers do pasteurize their silk and disilfect medical equipment as well. Life is too intrusive and too eager for food to not care about it.

> When in silico life becomes reality and humans do their human thing of devaluing anything that's not like them

That is, again, begging the question.

I'm not sure it is begging the question, at least not if framed properly.

The question seems to be to be "what exact criteria categorises what is commonly meant when people talk about what is alive". I think you could interpret OP as claiming that there is an idea of artificial or alien life as presented in science fiction which people would commonly describe as life but may not replicate.

That's not what the OP claimed, and in a second comment he/she implies AI life forms are inevitable. This is... debatable, to put it mildly.

You cannot say "this definition of life fails to account for an uncertain future phenomenon not everyone is convinced will count as life, therefore your definition of life is incomplete".

Fictional life is not real life. Authors, especially fiction authors, are not bound by the rules of nature. Sometimes they guess right, sometimes they don't, sometimes they simply provide thought experiments or parables.

A bee hive and a country fit this definition. Is that intended? I'm not against it.

This seems like a higher order definition.

Bees and Humans fit the definition. Therefor, aggregations of bees and humans, like hives and countries, also fit the definition.

"Countries" seem more of a stretch, as replicating would technically mean creating other countries like itself. Not just sustaining itself into the future.

Do hives seed other hives? I suppose they would, so they better fit the definition.

Individual humans don't quite fit the definition, many don't reproduce at all, the ones that do only do in groups of two. Strictly speaking you'd have to wait and see whether a given human child eventually reproduces to decide it's alive...

But with bees it's much worse -- in each hive, only the queen and some drones reproduce, most bees are worker bees that can't. So this definition fits bee hives better than it does individual bees.

Seems the definition would need to say something about the species as a whole reproducing. But that leads to the species definition problem. And what about that tortoise that was the last of its species?

> "Countries" seem more of a stretch, as replicating would technically mean creating other countries like itself. Not just sustaining itself into the future.

The world is full of countries, nations and so forth. At some time in the distant past there was no nations. After that there was one. Now there is over a hundred, with the corpses of many more lying in our past.

All usable land on Earth has been claimed now so they have no space to grow in number without cannabilising one another. Their walls have grown hard and inflexible with the passage of time and laws and agreements, and the evolutionary pressures of conflict have subsided of late, as they cannot move against one another without incurring the wrath of alpha predators, and the alpha predators cannot attack one another without the assurity of mutual destruction.

But countries live a long time, and their frame of reference is different from our own. Their moods encompass entire generations of the lives of mankind. They will eventually again fight among themselves unless ordered into cells within a higher organism. They will fight and devour one another, birthing new border states or vassal states. To any greater being it would appear like an almost peaceful dance, the ebb and flow of lines on a map, the respiration of civilisation.

To us it would be every bit as savage and chaotic as it must be for the cells and bacteria which comprise us.

And some day it'll start again when they can colonize foreign planets.

Well EO Wilson posited certain eusocial insect colonies, including bees, as a super-organism. I think the idea has some currency in biology. The idea is that Darwinian selection is acting upon the colony, so it is the unit of evolution. Remember that eukaryotic cells are a symbosis of two prokaryotic cells.

Not sure how often or even if countries self-reproduce.

> Not sure how often or even if countries self-reproduce.

Colonialism and independence.

I'm mulling this over... It's an interesting idea for sure. I'm not sure that it can't be reduced to human populations in general, which makes it more like the super-organism Wilson describes.

OTOH, not all human populations are states, as in countries, and arguable that is the "organism" said to be reproducing itself....

Are people who are sterile, and therefore incapable of #3, no longer alive?

Cells self-replicate. Cells are alive. People are composed of cells. Therefore, people are alive. Sterility is irrelevant.

following the same logic (AFAICT):

People self-replicate. People are alive. Societies are composed of people. Therefore, societies are alive.

(may or may not be a hole in your argument depending on whether you think a society is "alive")

Don’t know why you were downvoted, this is exactly it. Is a book club alive because all its members are alive?

I'd think of those as shared properties rather than definition of lives

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