If you took a visual snapshot of a recent corpse that hadn’t had time to cool down and a live body, would there be any differences?
If not, what are the differences?
I guess there’s a beating heart although it’s conceivable that, with the right technology, someone could go on without a beating heartand yet we wouldn’t think the person is dead.
Is it the flowing blood which brings fuel and oxidizer to energy-consuming body parts?
Is it electric impulses in the nervous system?
Is it something else?
This is not an abortion thread. Please do not bring up foetuses even if it’s germane. I would ask the mods to be strict about any abortion-related tangent otherwise it’s going to be impossible to discuss this sort of question without being derailed by axe-grinding.
A thing that isn’t living is not metabolizing, is not reproducing, its cells are not dividing. Different definitions may apply depending on the animal. I deliberately made my definition broad enough to cover sponges or a human kidney, because that stays out of the thorny ground of consciousness or human consciousness.
The Biology 101 answer to this is that “life” is recognized when an organism has the qualities of:
**organization **(being made of one or more cells, not a jumble of undifferentiated molecules)
**metabolism **(sometimes called “digestion”)
a mechanism for maintaining homeostasis
capacity for growth response to stimulation
potential for **reproduction **(of course an individual specimen may be infertile, but that doesn’t make it not alive)
capacity for successive generations to **adapt **to the environment through natural selection
The bolded ones are the key words most people use to remember the list.
self-sustaining within a well-defined environment (from which it is distinguishable)
capable of adapting to changes in its environment given certain parameters such as types of change, rate of change and numbers of changes which happen simultaneously
I think by this definition it’s why you can say that a virus is alive but a prion isn’t.
I think any difference would boil down to the simple fact that somewhere within the corpse, some vital (heh) chemical reaction(s) has (have) stopped happening for some reason.
I wonder if we could find “life” in stars, for certain definitions of “life”. Since stars comprise, what, 90% of the known mass of the Universe, they’d be much more likely to harbor life. Of course, this wouldn’t be like life as we know it, probably not even made of atoms.
In a less philosophic and more medical vein, life (human) is generally equated with brain activity, in the sense that when there is irreversibly none, a person is medically and legally dead. Thiswikipedia article sums it up nicely.
Many of these responses have provided what seem to be qualities or effects of life. According to James Be Reichmann, life is the ability of a thing (organism) to move itself toward activity of some kind. “This motion must be centered within the living thing itself…Growth, repair, and reproduction are…incontrovertible signs of life…The living thing provides its own dynamism and the direction for the development that takes place within it.”
Full disclosure: Reichmann is a Jesuit working from an Aristotelian-Thomistic philosophy and eventually argues for the presence of a soul as the “first principle of life” in all living beings, but his argument is based on reason rather than faith.
Only if you use an analogous meaning of the word “growth.”
Also, the movement of a robot is pre-programmed from another source. Everything that we generally refer to as “living” has its own inherent code or predetermined structure toward which it grows. That’s not to leave out adaptation, mutation, etc., since adaptation is a change of that of the structure (which doesn’t destroy it) in order to fit the environment; and mutation, however beneficial, is a departure from the “source code.”
WhyNot’s answer is really as good as you’re going to get for a functional definition.
What I find very interesting is that parts of a recently dead corpse are still alive. You can isolate and culture cells given the proper conditions and those cells do continue to reproduce, metabolize nutrients, etc.
So a human being is a living thing composed of living things. As long as all the living things are working at some level of function and coordination, we’d say that the whole human is alive. When the function of the whole drops below a certain level, we can only point to individual components that might be called alive.
In fact… even looking at a single human cell, you see that it contains smaller mitochondria. Mitochondria reproduce independently within the cell, containing their own DNA even. It is conceivable that you could kill the cell and continue culturing the mitochondria.
So it really is a huge oversimplification to think of a human being as a single living entity. We’re really colonies.
Possibly even composite organisms such as lichens since we are only beginning to discover the extent of the interdependence between the biochemical processes coded for in our DNA and those of the multitude of organisms that make up our microbiome. In fact the new microbiome project will probably have the same impact as the human genome project did.
A bullet through your brain will kill you almost instantly. It will not instantly shut down all metabolism (of which the Krebs cycle is one aspect) in every cell of your body. Nor will other causes of death. Cellular metabolism will continue for many minutes or even hours, and if a cell was about to divide before the shooting, and it was well away from the site of physical damage, it is still going to divide. Eventually metabolic activity in the cells will run down because the heart has stopped and so the blood is no longer supplying them with fresh nutriment and oxygen, but that will take a little while, and until it happens the cells remain alive even though the person of which they were a part is not.
For the Krebs cycle, and other aspects of metabolism to run, you do not even have to have a living, intact cell, let alone a whole living organism. Generally speaking, it is by setting things up so that the Krebs Cycle, or whatever, can run outside of an intact cell, that biochemists are able to actually learn about these metabolic processes and how they work.
In my first lesson of high school biology, we learned a list that they called “The Seven Characteristics of Life”. It was more or less the same as what WhyNot said, and if you Google that phrase you will find numerous versions of the list (although I think the list I originally learned included excretion, and maybe left out adaptation). Life is a complex phenomenon, it needs to cover everything from humans to tape worms, oak trees, algae and bacteria. You cannot capture it with just a single, simple criterion. The “Seven Characteristics” is about the best, reasonably succinct answer that anyone has been able to come up with.