How does science define life?
If it helps, I believe a living thing:
A) gets nutrients
B) disposes of wastes
C) reproduces
D) responds to stumuli
E) …there was another bullet for this list, I believe…blasted freshman biology
What about a donkey?
Does it needs cells? (I should have asked this in the OP)
Try again. Fire does all of that:
A) consumes fuel
B) releases combustion products
C) can spawn smaller fires through disemination of sparks
D) moves towards sources of new fuel
As you can see, life is VERY hard to define precisely.
…what about it? Isn’t a donkey a cross breed of some sort? So it wouldn’t repro–
Ah.
I see.
Q.E.D., you never fail to show me up. 
Wait-- what about this? Am I reading it incorrectly?
I’m going to ignore the attempt at perverting facts until fire=life because sparks actually being a reproductive action of fire is just silly.
When I was in high school (granted, it was in Alabama), I remember that anything defined as living must be composed of one or more cells.
I remember this because then a virus is no longer considered a living organism. I argued that one for a long time saying, “If you agree that you can kill a virus, it must living. You can’t kill what was never dead.”
Really, though, it may just depend on your own interpretation as to what life actually is because there tends to always be an exception, even to what is living and what is not.
And (blast, triple post–crud. Please don’t mod me; I’m only trying to help!) from here:
It was a demonstration (and not an original one, I must admit) that simplistic definition are inadequate when attempting to define what “life” is:
From this article, and interesting discussion of the definition of life.
Cecil speaks on Why don’t we consider fire alive? What is life?
Just for the record, I wasn’t suggesting fire is alive, in case you missed my point.
In the biological sciences, something is deemed to be ‘living’ if it exhibits certain properties:
- autonomous identity
- growth and development
- response to environmental stimuli (known in some old-fashioned textbooks as ‘irritability’, oddly enough!)
- ingestion
- excretion
- reproduction / propagation
- homeostasis (regulation of factors such as temperature, humidity, pressure within a ‘tolerable’ range)
This is a simple list, and simplicity always comes at a price. For every single property on the list, one can always suggest an example which presents difficulties of strict definition. Also, the further down the microscopic level you go, the harder it gets to observe such hard and fast distinctions, leading to endless debates about what is and is not ‘life’. We can leave these fine details to those who need to wrestle with them, such as theologians and doctors on ethics committees. Most of us are concerned with things bigger than specks of dust, and the above list holds up pretty well when you want to tell rocks from swans.
More generally, ‘organic’ chemistry simply refers to the carbon-based chemistry typically found operating at the cellular level in high-order animals.
Of course, if you try to define 'intelligent life’ it gets even harder, because intelligence tends to be easier to recognise than it is to define. The first rule is simple: if it posts on the SDMB, then it’s intelligent (with a few spectacular exceptions). More generally, for higher-order species, intelligence is most easily defined as ‘the apparent purposeful pursuit of optimised strategies for survival, reproductive success and comfort’.
Basically, living things try to eat, get laid and get comfy. Non-living things don’t.
Ten bucks says this makes someone’s sig line in the next three days.
Who should he make the check out to?
Ah, Q.E.D., you always brighten my day.
All checks payable to QueenOfTheShire, tyvm!
Q.E.D. I feel suitably proud and honoured.
Bah! that’s easy; only the queen can eat swans, whereas anyone can eat rocks, if they wish to.
Life is just a dumb word denoting a dumb idea.
This is a guess, but I suspect Golfer meant to ask about “mules” rather than “donkeys”; a mule is a cross between a male donkey (a jack), and a female horse (a mare). It is a sterile hybrid.
Not that it is really relevant, but I dimly recall that when Larry (of "Larry, Darryl, and Darryl) took an exam for his G.E.D. in an episode of , Newhart, he listed “partying” as an essential characteristic of living organizisms instead of reproduction. Rising to his defense, Bob Newhart argued that this was maybe a matter of semantics…