The last post and some recent conversations have really got me thinking about this. Just what does it mean to be alive? What is life?
Can this be answered purely in the realm of science? I’m not totally sure. If criteria could be defined for life and then measured for things, then yes. But, I don’t think we can define life in a 100% purely objective sense. At the very least, there will be massive arguments about the various definitions that could appear.
On the other hand, science (and related systems) give us the only possible route to a robust, coherent, and consistent definition of what life is.
The concept of alive is just so variable. Most people would have no trouble putting down a beloved pet who was hit by a car and is brain dead. Brain dead in this case means “can’t think, can’t control voluntary muscles, may or may not have autonomous muscle action”. Yet those same people will argue that the exact same situation applied to their sister or mother or grandfather is not the same and will keep that person on life support until the heat death of the universe.
I will note here that many governments don’t care what you think and will make the decision to keep a human being on life support indefinitely. Many doctors will too.
This runs a little afield of my initial question, but it’s something to consider. I think a requirement for being alive should be “Response”. Every living thing that we are aware of and every non-organic living thing that we can imagine or build presently has this characteristic. It responds. It responds to external environmental ques (mates, food, fear, too hot, etc). It responds to internal ques (hungry, scared, hurt, etc.). For higher organisms we have to consider both reasoned responses and autonomous responses.
If a dog or a human being can no longer respond, then is it really alive. And I don’t mean, “it can sense fear, but it can’t make muscles work” lack of response. Medical technology is perfectly capable of measuring brain and spinal activity. Open the eye, shine a light in. Does the pupil respond? Does an EEG record brain activity in the visual region? These are the kind of responses I’m talking about here.
Sure, the cells might be using energy, but without medical intervention, there is no way for the cells to get more energy (or proteins or extrude wastes).
Even computers respond. Presumably, artificial intelligence will respond as well. If it doesn’t respond, then it might as well be a brick.
Finally, we would need to ask, is there any chance of resuming normal functioning? This is a good point for science to come in. Many people will wait for and pray for ‘a miracle’ to save uncle Whatshisface. They will demand doctors keep their beloved uncle on life support until the deity of their choice restores them to full function (preferably by next weekend so that they can make a chocolate pie for the reunion). But, how many times has someone who was clinically brain dead returned to life?
None. I’m not talking about persistent or permanent vegetative state here. We’re talking about brain death. The brain is dead. We get into a whole ‘nother can of worms with vegetative states.
Again, I’m running afield of the intended post, but this is a pretty interesting question in and of itself.
So I think ‘response a stimulus’ is a valid requirement for something to be alive.
Is response all that’s needed? No, I don’t think so. But I think it’s a big part. Computers respond, but I don’t think we’ve create computers that are alive yet.
Does something that is alive have to be made of cells… or even organic? No, I don’t think so. We haven’t created strong AI yet, but I suspect that if it is doable, then we will have to rewrite much of what we consider ‘alive’ means.
The requirement that a living thing be made of cells is sort of a classical definition of life. The good point is that it is a very clear demarcation line. Cells on one side, no cells on the other. Life, non-life. Easy. I just don’t think that it’s a valid demarcation line. Very few things (especially in biology) are ever this cut and dried.
I think, pretty soon, we (as a species) will have to make a decision about something being alive that isn’t made of cells. Will be able to make this call?
What about energy? One of the hallmarks of living things is the use of energy. All living things that we are aware of (and all we can imagine) have to have energy. This is actually an easily provable statement. It all has to do with thermodynamics. Living things absorb energy to replace the energy lost in doing the functions of living things. Without a constant influx of energy, a living thing would run out, and then would not be able to perform its functions anymore.
The maintenance of homeostasis is another classical part of the definition of a living thing and I think this has some merit for organic systems, but may not apply to non-organic systems.
Basically, homeostasis is the act of keeping one’s self at a variety of conditions that are appropriate. Humans need to be about 98F. We have a variety of internal systems (and external ones) to help us maintain this temperature. But homeostasis applies to everything from water content to many, many chemicals, compounds, and elements. There are many internal conditions to monitor and control (pH, salt concentration, etc.)
A living thing should be able to take care of itself. I can see some non-organic systems potentially needing a helper for some internal conditions. So, this one is a maybe.
There are other things to consider. I suspect that we will revisit this in short order.