[MarianaM (OP)]

Dhruv asks...

What is life in biological terms? What parameters are considered to declare a thing as living?

What's the answer?

[alancalverd]

Living things transpire, either oxidising carbon compounds to produce energy, or using some other form of energy  (solar, volcanic, etc) to produce complex carbon compounds from inorganic molecules. 

[Halc]

What is life in biological terms?

Asking in this way already assumes that life must be biological, hence any answer given will not be useful when deciding if some newly discovered thing (on a new planet say) is life or not.

So the answer to the question above is: It is life if you and it share a common ancestor.

[hamdani yusuf]

So the answer to the question above is: It is life if you and it share a common ancestor.

What about fully synthetic bacteria?

[alancalverd]

deciding if some newly discovered thing (on a new planet say) is life or not.So the answer to the question above is: It is life if you and it share a common ancestor.

That's a very prejudiced religious statement! Since life evolved from non-life on this planet, it could equally have evolved elsewhere in the universe with no common ancestry.  And whilst some people might claim to trace my ancestry back to Adam, any anti-Semite would be horrified at the thought of common ancestry

[Hayseed]

Can assemble(grow) matter.  Most Replicate.  Then dissolve.

[alancalverd]

Mules don't replicate, but they are alive.

[Halc]

So the answer to the question above is: It is life if you and it share a common ancestor.

What about fully synthetic bacteria?

If it's bacteria, then its genetics has been copied (and perhaps modified) from some sample, making it related to that sample.
Thinking about this brings up an interesting point about being related to something.  Bacteria doesn't really have ancestors, and hence I'm technically not related to it by the exact wording I used.

[Hayseed]

Asking what causes life is like asking what caused the cosmos.  We can not discover or determine these things.

We can only study and describe the activity of the present.  What life is doing now.  Life is completely different from nature. Life has a transmittable code(information), thru off spring.

The only thing that has permanence, is the code, which gets changed/adjusted along the way.

And the physical result is, a self adjusting biosphere of duration.

This extra life force/property is only detected on earth.   And it is an extremely stubborn force.

The nature of the cosmos can make atoms, elements and certain molecules. And all this nature follows a set of rules, which can not be changed by nature.  It's limited.

But this life force can build very complicated molecular structures, and give the structures function and animation.  Structures building structures.  Something happens here that is very unique, growth.  And as a double whammy.......reproduction.  And a final bummer......an unavoidable tragedy, death.  We are a stepping stone.

[alancalverd]

Life has a transmittable code(information), thru off spring

I have huge, sterile trees in my garden - no transmissible code, but you can grow another tree from a cutting, and they are definitely alive. I have live human friends whose genetic code is not transmissible. Monsanto have spent a fortune patenting sterile wheat. Most bees are sterile. Reproduction is not a necessary characteristic of life.

Nobody has ever detected a "life force". Its existence is only demonstrated by its absence! There are plenty of candidate planets in the universe where terrestrial chemistry is possible, but we haven't explored them yet.

We don't know that the "rules" can't be changed. All the evidence suggests that they changed significantly about 13.5 billion years ago in this corner of the universe, and they are in any case descriptive, not prescriptive.

Death is not a tragedy. It is essential for the life of animals that plants die, and vice versa, and if we did not die the world would be full of old people with no room for our offspring. Some deaths are inconvenient but the graveyards are full of people who considered themselves indispensable.

[Hayseed]

All context has a bell curve.

[hamdani yusuf]

Mules don't replicate, but they are alive.

Right. But the cells making up the mules do replicate.
I think it is possible to use technology to make mules reproduce, perhaps by modifying some of the genes that prevent proper conception and gestation.

[alancalverd]

If you modified the genes of a mule, it wouldn't be a mule.

A mule is the offspring of a male donkey and a female horse. Horses and donkeys are different species, with different numbers of chromosomes.

[hamdani yusuf]

If you modified the genes of a mule, it wouldn't be a mule.

A mule is the offspring of a male donkey and a female horse. Horses and donkeys are different species, with different numbers of chromosomes.

Not necesarily. A few percentage of non-african modern humans' genes came from Neanderthals and Denisovans. We still call them humans. Humans with a few novel mutations are still considered human. I don't know how much genetic change is the threshold to stop calling them humans. Ditto for the mules.

[alancalverd]

There is no consistent definition of "species"  - it's a label of convenience for whatever is different from anything else. But a mule (equus mule) is an animal bred from a female horse and a male donkey and they are all sterile but alive. By all means muck about with the genes and make something that looks like a mule but is fertile (you will probably need to make two!)

[evan_au]

Mules don't replicate, but they are alive.

A horse has 64 chromosomes and a donkey has 62. A mule inherits 63.An even number of chromosomes is needed to divide into pairs and reproduce.

In other words,
- Mitosis (normal cell division) can work with 63 chromosomes: Each mule's "daughter" cell ends up with 63 chromosomes, and survives.
- But Meiosis (production of egg and sperm) takes matched pairs of chromosomes, and puts one of each pair in the egg or sperm cell.
- In a mule, there is one chromosome with no partner.
- So the egg or sperm can end up with a random mixture of horse and donkey genes, with or without the extra horse chromosome.
- The odds are greatly against it, but it is possible that the egg or sperm could end up with 100% horse or 100% donkey DNA, which would be fertile.

For an exception, see: https://www.denverpost.com/2007/07/25/mules-foal-fools-genetics-with-impossible-birth/

[cleanair]

Asking what causes life is like asking what caused the cosmos.  We can not discover or determine these things.

Why do you consider that statement to be valid?

[alancalverd]

Valid, because it contains a subject, verb and object that plausibly relate to each other. Whether it is provable is an entirely different matter! 

[Hayseed]

It's been a valid statement so far.  Does anyone know how the cosmos started?  Do you believe that we can "discover" how it was started?  How are you going to do that?

Do we even understand, what we are looking at?

Same with life.   No one has ever seen it start.  It is passed, not started.

Will we ever understand the passed on life, in order to be able to start it.

Could it be possible......that new life can not be started at the present time?

Is it possible for a new cosmos to form now?

Is life in it's own separate "time zone"?  Like light.

Let's first try to answer the questions that we CAN answer............it MIGHT change the way we ask the BIG questions.  And look for those answers.

[alancalverd]

Obviously we can't literally discover something that has already happened, but we can put together a plausible hypothesis of how. This leads me to wonder why anyone would bother. Apart from idle curiosity, that is. Do you want to build another cosmos?

As far as we know, life is a very improbable, complicated and temporary phenomenon, but there is no reason to think it hasn't happened elsewhere or won't occur somewhere else in the universe at some time, or that biogenesis is dependent on a law of physics that has been repealed. We have found (indeed we are) one needle in a haystack, but that finding doesn't preclude the possibility of others or imply a magical haystack.