# Biologically, what is life? (not an abortion thread) **URL:** \ **Category:** Factual Questions\ **Created:** [March 2, 2013, 12:29pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816 "2013-03-02T12:29:16Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\ **Post date:** [March 2, 2013, 12:29pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/1 "2013-03-02T12:29:16Z")
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. ---
**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\ **Post date:** [March 2, 2013, 12:38pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/2 "2013-03-02T12:38:15Z")
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. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [March 2, 2013, 12:43pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/3 "2013-03-02T12:43:50Z")
Absence of the Krebs cycle in the corpse. ---
**Author:** ![WhyNot](https://avatars.discourse-cdn.com/v4/letter/w/c77e96/32.png) [@WhyNot](https://boards.straightdope.com/u/WhyNot)\ **Post date:** [March 2, 2013, 12:48pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/4 "2013-03-02T12:48:35Z")
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. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [March 2, 2013, 1:14pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/5 "2013-03-02T13:14:40Z")
[A relevant Cecil column](http://www.straightdope.com/columns/read/1255/why-dont-we-consider-fire-alive-what-is-life) regarding whether ‘fire’ is alive… ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [March 2, 2013, 2:50pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/6 "2013-03-02T14:50:25Z")
fI like this definition: 1. self-sustaining within a well-defined environment (from which it is distinguishable) 2. 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. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [March 2, 2013, 3:22pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/7 "2013-03-02T15:22:44Z")
> [@MichaelEmouse](#): > > 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 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. ---
**Author:** ![BrotherCadfael](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@BrotherCadfael](https://boards.straightdope.com/u/BrotherCadfael)\ **Post date:** [March 2, 2013, 4:51pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/8 "2013-03-02T16:51:08Z")
Here’s one take on it, from a 1930 murder mystery: > [@Dorothy L. Sayers](#): > > ‘What is Life?’ I asked, suddenly. > > ‘Well,’ said Waters, ‘if we could answer that question we should probably not need to ask the others. At present – chemically speaking – the nearest definition I can produce is that it is a kind of bias – a lop-sidedness, so to speak. Possibly that accounts for its oddness.’ > > ‘I’ve said that kind of thing myself,’ I said, rather astonished, ‘just as a sort of feeble witticism. Have I hit on something true by accident?’ > > ‘More or less. That is to say, it is true that, up to the present, it is only living substance that has found the trick of transforming a symmetric, optically inactive compound into a single asymmetric, optically active compound. At the moment that Life appeared on this planet something happened to the molecular structure of things. They got a twist which nobody has ever succeeded in reproducing mechanically – at least, not without an exercise of deliberate selective intelligence, which is also, as I suppose you’ll allow, a manifestation of Life.’ The science is, I suppose, just a bit dated, but this question was essential to the solution of the mystery. You can find the text of the novel [here](http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&ved=0CEUQFjAD&url=http%3A%2F%2Farthursbookshelf.com%2FHorror%2Fsayers%2FThe%2520Documents%2520in%2520the%2520Case%2520-%2520Dorothy%2520L.%2520Sayers.pdf&ei=JC0yUcy4G5Ki8gTKwIDQAQ&usg=AFQjCNHJ62oDnJljngCkweZAQFvhsdjr9Q&bvm=bv.43148975,d.eWU). (PDF warning) ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [March 2, 2013, 4:57pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/9 "2013-03-02T16:57:29Z")
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. ---
**Author:** ![Oly](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/oly/32/8255_2.png) [@Oly](https://boards.straightdope.com/u/Oly)\ **Post date:** [March 2, 2013, 5:42pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/10 "2013-03-02T17:42:00Z")
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. [This](http://en.m.wikipedia.org/wiki/Brain_death)wikipedia article sums it up nicely. ---
**Author:** ![BlueMit11](https://avatars.discourse-cdn.com/v4/letter/b/7feea3/32.png) [@BlueMit11](https://boards.straightdope.com/u/BlueMit11)\ **Post date:** [March 2, 2013, 6:48pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/11 "2013-03-02T18:48:54Z")
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. Source: Philosophy of the Human Person ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 2, 2013, 9:14pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/12 "2013-03-02T21:14:46Z")
> [@](#): > > According to James Be Reichmann, life is the ability of a thing (organism) to move itself toward activity of some kind. How would that definition rule out, say, a car? ---
**Author:** ![Darth\_Panda](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Darth\_Panda](https://boards.straightdope.com/u/Darth_Panda)\ **Post date:** [March 2, 2013, 9:17pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/13 "2013-03-02T21:17:29Z")
> [@Chronos](#): > > How would that definition rule out, say, a car? The car can’t move itself. Something alive has to intervene. ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [March 2, 2013, 9:38pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/14 "2013-03-02T21:38:03Z")
> [@Darth\_Panda](#): > > The car can’t move itself. Something alive has to intervene. Or forget to set the parking brake. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [March 2, 2013, 9:38pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/15 "2013-03-02T21:38:46Z")
> [@BlueMit11](#): > > 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.” By this definition, it would take maybe 15 minutes to create a robot that is alive. ---
**Author:** ![BlueMit11](https://avatars.discourse-cdn.com/v4/letter/b/7feea3/32.png) [@BlueMit11](https://boards.straightdope.com/u/BlueMit11)\ **Post date:** [March 2, 2013, 9:59pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/16 "2013-03-02T21:59:04Z")
> [@Blake](#): > > By this definition, it would take maybe 15 minutes to create a robot that is alive. 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.” ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [March 2, 2013, 11:04pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/17 "2013-03-02T23:04:09Z")
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. ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [March 2, 2013, 11:18pm UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/18 "2013-03-02T23:18:44Z")
> [@dracoi](#): > > 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](http://www.sciencedaily.com/releases/2013/02/130228093831.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+sciencedaily%2Fhealth_medicine+%28ScienceDaily%3A+Health+%26+Medicine+News%29&utm_content=My+Yahoo) will probably have the same impact as the human genome project did. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [March 3, 2013, 2:01am UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/19 "2013-03-03T02:01:07Z")
> [@HMS\_Irruncible](#): > > 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. > [@kayaker](#): > > Absence of the Krebs cycle in the corpse. 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. ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [March 3, 2013, 2:12am UTC](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816/20 "2013-03-03T02:12:27Z")
> [@njtt](#): > > The “Seven Characteristics” is about the best, reasonably succinct answer that anyone has been able to come up with. But it might be too “earth-centric”, IOW it just describes what we already know. What if you want to describe what you don’t know yet? [Next page](https://boards.straightdope.com/t/biologically-what-is-life-not-an-abortion-thread/651816.md?page=2)