Is there inherently anything “alive” about a singular cell? I know it fits the criteria for living but is it not just a bunch of complex chemical processes on repeat?
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Is that not true for all living things? One cell is alive for all practical purposes, but also “nothing more than a machine”. A multicellular organism is just a bunch of machines.
Your question is more philosophical than scientific one. Is human even alive, when all we are is just bunch of complex chemical processes on repeat? Are viruses alive?
Generally, we consider matter to be a form of life when:
* The matter has biological processes (*e.g.*, signaling, threat avoidance, temperature regulation)
* Has the capacity for growth (rather than accretion)
* Reacts to stimuli
* Has a complex metabolism
* Transforms energy (such as through digestion or movement)
* Can reproduce
* Has genes and is capable of evolution
Sometimes these are clear to see and sometimes they are not. Famously, viruses are quite good at reproducing, are capable of evolving, and have genes but they don’t have most of the other characteristics, so we’re not comfortable considering viruses to be “alive.”
>just a bunch of complex chemical processes on repeat?
I mean, you’ve basically just hit on the definition of life, there. Life is a series of chemical processes that are capable of signaling and reacting to stimuli, and that are capable of replicating and sustaining themselves. A bacterium or other single-celled lifeform by this definition is every bit as alive as you or me.
Everything else that we like to tack on regarding life – thought, feeling, meaning – that’s all just the human condition, that’s our own baggage tacked on to what biology is forming. If we found self-replicating single cells on another planet, we’d have found life out there in the universe; the simplest form of life, but life nonetheless.
“Life” is just complex chemical reactions on repeat that result in an expansion of those chemical reactions. Anything that meets those standards – including a single cell – counts as life.
if it breathes, it lives?
I think the word you’re looking for is “conscious”.
Cells are “alive”, because they can replicate, but this is unsatisfying if you’re using the colloquial/traditional version of the word alive. Intuitively there is more to being “truly alive” than the strict criteria that scientists use for the term. You feel that YOU are alive. You are experiencing and thinking and contemplating and planning, etc.
Organisms that have this vague fuzzy version of “truly alive” are called “conscious”. Unfortunately, the idea is so fuzzy and ill-defined that testing it proves a challenge. We don’t really know how to check if something is “truly alive” and we don’t have any evidence that it is even possible to check.
After all, everything that we understand about how we work can be explained away by many many many chemical processes. It’s not awfully clear that there is any special non-chemical process going on. We all know that there we have some sort of awareness. Maybe that is special to us? Maybe all animals have something approximating what we all seem to have? Maybe you are the only one that has this separate experience and everyone else is just a convincing mindless zombie. Maybe literally every chemical process has some degree of this awareness and it isn’t special at all. We just don’t know anything about it or what it is.
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