-1

High school students in India under the CBSE Board are taught that consciousness is a defining property of living organisms. This question lies under the topic of 'What defines living organisms?' Does that mean that if robots and other artificial intelligence have consciousness and can react to some external stimuli (just like plants), they are alive? Also, what about the patients in coma or those who are 'brain-dead', are they alive or dead?

Then, how do we define living in terms of science?

A possible answer in my opinion to the second question above could be that life begins at conception and an organism is considered alive till the point where it has no differences with the dead; i.e. a person who is 'brain-dead' would still be considered alive because he/she still isn't the same as a dead person.

So should consciousness be a defining property of living organisms?

Edit: Defining Consciousness-
In the NCERT textbook which is used to teach the CBSE high school students in India, consciousness is explained as the ability to sense the surroundings or environment and respond to the environmental stimuli which could be physical, chemical or biological.




For reference: NCERT Class 11 Biology Textbook~ Unit 1: Chapter 1, Page 5 (second paragraph) Link to book: 1http://ncert.nic.in/textbook/textbook.htm?kebo1=1-22

Roger Baker
  • 9
  • 4
  • 6
    Define consciousness. Is a bacterium conscious? How about a potato? Seems like an appropriate question for the (insert choice of religion) site. – jamesqf Jan 05 '20 at 18:34
  • @jamesqf It is mentioned in the textbook that, 'All organisms, from the prokaryotes to the most complex eukaryotes can sense and respond to environmental cues.' So this should mean that bacteria and potatoes are indeed conscious as they can react to external stimuli. I've edited the answer and added the link to the book, you can check it out. – Roger Baker Jan 06 '20 at 15:24
  • 1
    Someone in a coma doesn't respond consciously, but their body absolutely continues to sense and respond to stimuli. A brain-dead person can still maintain body temperature, metabolize nutrients, and maintain blood pH, none of which are possible without some kind of feedback loop that requires response to the environment. Consciousness could be a necessary condition of life, but it's certainly not sufficient - my TV isn't "alive" even though it responds to the stimuli of me pressing the buttons on the remote. – Nuclear Hoagie Jan 06 '20 at 15:27
  • 1
    As someone who studies consciousness...that definition of consciousness would be a very unusual one in the field. – Bryan Krause Jan 06 '20 at 15:51
  • in my long-ago high school textbook this was defined as "irritability" (i.e., the capability of sensing and responding to changes in the environment). This is mentioned in the Khan Academy materials – Ben Bolker Jan 06 '20 at 16:56
  • @Roger Baker: But in aany semiconductor catalog, I can find a large number of little pieces of doped silicon that sense environmental cues, and wire up circuits that will respond to them. Heck, I'm writing this on one such thing: my computer senses the environmental cue of me pressing keys on my keyboard, and responds by drawing characters on the screen. It senses the environmental cue of CPU temperature, and responds by turning on the CPU fan when it gets too warm, Does that mean integrated circuits are alive? – jamesqf Jan 07 '20 at 05:17
  • @BenBolker Thanks for your input, the linked resource also comes up with the same conclusion: consciousness is not a defining property. – Roger Baker Jan 07 '20 at 19:31
  • @jamesqf: I'm so glad that you have come to this conclusion because that exactly is my question too. Perhaps, consciousness is not the right property that can define living organisms as opposed to the non-living. Or maybe, we could come up with a better description of what's 'living' and 'non-living' to clear up the confusion.
    And conclude that consciousness should NOT be a 'defining' property as mentioned in the textbook.     – Roger Baker Jan 07 '20 at 19:33
  • @Roger Baker: I think the problem is that the authors of that text are using the word consciousness in a way that's far different from general use. Which is why I think it's really more of a religious question than a scientific one. – jamesqf Jan 08 '20 at 04:45
  • Hi and welcome to Bio.SE! No, consciousness should not be the threshold for being living since it only exists in animals, and even then it is very hard to define and measure. Behaviourism is one way of looking at this. I asked a question a while ago about why viruses don't meet the definitions of being alive here which might answer some of the things you are interested in. – James Jan 09 '20 at 11:32
  • 1
    I have to mirror Jamesqf here there are many very different definitions of consciousness, many with a lot of baggage attached. which is why a good definition would avoid the word entirely. – John Jan 09 '20 at 14:29

1 Answers1

0

tl;dr this is an extremely unusual definition of "consciousness" (I'd be surprised if you can find it in any standard English dictionary). If you prefer, like Humpty Dumpty in Lewis Carroll's Through the Looking Glass, to define words (in this case "consciousness") in any way you want — i.e., as above ("ability to sense the surroundings or environment and respond to the environmental stimuli ..."), then consciousness is indeed one of the defining characteristics of life.

This property is (arguably) necessary, but not sufficient, for life — things can be 'conscious' (respond to stimuli) but not be alive, but they can't be alive if they don't respond to stimuli.

This property is more typically called irritability. The Khan Academy article on "What is Life?" gives this property under the section "Response" (along with the the other properties "Organization", "Metabolism", "Homeostasis", "Growth", "Reproduction", "Evolution"). (You can also find it in lots of biology textbooks in this Google Books search.) The text you refer to uses similar criteria (growth, reproduction, metabolism, cellular organization, 'consciousness').

As Khan Academy also says, it's hard to be precise:

Living organisms have many different properties related to being alive, and it can be hard to decide on the exact set that best defines life

So, to answer your specific examples:

  • robots respond to stimuli (and, arguably, have organization and metabolisms), but they don't grow or reproduce. If they did, we might call them living organisms.
  • people who are brain-dead or in a coma still exhibit some degree of response to the environment/irritability. So do dormant seeds, spores, and other "resting stages" of organisms.

There are always edge cases; is a sterile person (or indeed one who can't reproduce because they're in a coma) "alive"? The Khan Academy web page uses a similar example, the case of mules (the infertile hybrid offspring of horses and donkeys), along with several other examples that illustrate some of the more difficult cases (dieocious/gonochoric organisms that are isolated from members of the other sex [can't reproduce, but still considered alive]; fire ["reproduces" but not organized or homeostatic]; crystals [not homeostatic, don't evolve]).

Ben Bolker
  • 5,354
  • 19
  • 33
  • And the edge cases can be even edgier. Consider HeLa cells https://en.wikipedia.org/wiki/HeLa or women in comas who've been raped by their attendants and become pregnant. – jamesqf Jan 08 '20 at 04:48
  • I don't think this answers the question (which I doubt could be answered on stack exchange...). "Life" in biology typically do they have the biological machinery to replicate at the cellular level given enough resources. For almost all life, that comes down to does it have ribosomes. – James Jan 09 '20 at 11:42
  • @jamesqf This is not a fringe case at all. HeLa cells are universally considered an in vivo ("within life") experiment. I don't understand why the rape example would be a fringe case. – James Jan 09 '20 at 11:43
  • The title of the question is not "how do we define life?", but "should consciousness be a defining property of living organisms?" (to which the answer is, "yes, if you define 'consciousness' as ability to respond to changes in the environment) – Ben Bolker Jan 09 '20 at 13:59
  • @James: HeLa cells are a fringe case because they're living cells derived from a person who once was conscious, but who is now dead. So are the cells "conscious"? Likewise the brain-dead rape victims. Not conscious by common definition, but still able to reproduce. – jamesqf Jan 09 '20 at 17:54
  • @BenBolker That definition is far too nebulous to be of much use in biology. Your roaring fire in a hearth will leap around when poked, whereas an oak tree wouldn't even flinch if I prodded it twice as hard! Being less pedantic, viruses respond in a very biological manner to their environment. Are they "conscious" in any meaningful way? A much more useful measurable and comparable classification for life is "does it have (active/translating) ribosomes in it"? There isn't really a need to drag any other qualifiers in. – James Jan 09 '20 at 18:49
  • @jamesqf This is starting to sound an awful lot like the definitions of a soul... – James Jan 09 '20 at 18:50
  • My final comment: as I say in my answer above (as do the various sources cited), (1) "response to the environment" is a necessary but not sufficient condition (i.e. 'fire responds to the environment' does not by itself imply fire is alive); (2) the particular environmental changes that organisms respond to vary enormously. Trees respond to changes in light, distribution of nutrients and water in the soil, etc.. I think my post is a reasonable answer to the OP's question; if you disagree you can downvote (if you haven't already); post your own answer; or vote to close the Q. – Ben Bolker Jan 09 '20 at 18:54
  • 1
    @BenBolker I think my overall point is that those irritability concepts are too soft, hard to define, and non-comparable between organisms without more qualifiers. I've voted to close the question. I agree that your answer is very reasonable. I just don't think any answer would completely answer this question. A more comprehensive essay on the topic of life is this Science editorial: The Seven Pillars of Life. It reframes the irritability as "adaptability" and "improvisation" I suppose. – James Jan 09 '20 at 19:36
  • @James: Exactly, which is why I say it's a question better suited to religion sites, or maybe philosophy, rather than biology. – jamesqf Jan 10 '20 at 20:06