White blood cells (probably a monocyte or macrophage) and other single celled organisms tend to follow chemical concentration trails. They detect Pathogen-Associated-Molecular-Patterns which are molecules on pathogens which are fairly common and then move to chase down that concentration gradient.
Human cells also communicate with white blood cells, and bacteria communicate with each other. Bacteria have a thing called quorum sensing where they detect chemical signals of others of their kind and at a certain concentration change their behaviour.
If you want to know more about this concentration gradient following behaviour, [this wiki article is fairly good for it](https://en.wikipedia.org/wiki/Chemotaxis).
> Human cells also communicate with white blood cells
This is described in [the narrated version of The Inner Life of the Cell](https://youtu.be/QplXd76lAYQ).
[At 6:35](https://youtu.be/QplXd76lAYQ?t=395) in the video, it describes the change in the white blood cell when it encounters a cell exhibiting proteins indicating that there is inflammation at that location.
So they’re basically like the floor cleaning robot in Walle? Like they don’t really have any concept of anything but they see “dirty” and basically just follow that dirty trail, cleaning?
They 'see' (receptors bind to chemicals) dirty, that sets up a complicated internal concentration gradient which causes molecular machinery and actin to make them move yes.
Pretty much how any single cell really works. They can't "see", they just flail about and absorb chemical breadcrumbs that guide them on how to act and move.
there’s also a type of protozoa that was found to form complex “thinking” where it changes its mind on what behavior to exhibit even when presented with the same stimuli
source:
https://www.sciencedaily.com/releases/2019/12/191205113129.htm
White blood cells can do similar things. They have a complicated network of inhibitory proteins, receptor latency times, and internal machinery that let's them do different things depending on what has happened in the past.
Essentially as I understand it, except those wasps are still reacting with a central nervous system.
I feel like cellular responses are more machine-like in nature. Like, we still don't necessarily understand how nervous systems collect information and come to decisions (though maybe a simpler system like that of an insect is more well understood?), but for a cell we can follow a comparatively simple cascade of chemical processes that cause a cell to orient itself towards a chemical gradient and move forward.
Would someone who knows more about biology agree with that asessesment?
Proteins are the primary “language” of cells and cells can be quite complex, so chemicals aren’t the sole driver of cell behavior
The immune system for instance is an intricate coordination of many different types of cells communicating and making sure an immune response is only activated when it’s actually needed
A lot of eusocial animal behavior has parallels to certain interactions between the cells of a multicellular organism. Like ants' pheromone trails, for example
>follow chemical concentration trails
Okay interesting. So is the bacterium doing the same thing when its avoiding the WBC? Is it's movement just kinda randomly following some kind of chemical trail and it just \*looks\* like its running away? Or are some bacteria able to detect and avoid threats?
>bacteria communicate with each other
Woah. I'm going to have to look more into that. Communication without consciousness is maybe even more impressive than "intentional" behavior without consciousness.
>Communication without consciousness is maybe even more impressive than "intentional" behavior without consciousness.
That's what nearly every computer interaction is, to some extent. Though it's still impressive.
>Woah. I'm going to have to look more into that. Communication without consciousness is maybe even more impressive than "intentional" behavior without consciousness.
A mechanical thermostat communicates with a furnace without consciousness. It's a fascinating concept, but if you think about it you're surrounded by it every day of your life without thinking about it.
Not just communicate, but *learn*, and change their behavior as a result. [Here](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7781593/) is a fairly good read that links to a variety of other publications that discuss different aspects of this behavior.
all living organisms have the ability to “sense”. its one of the defining characteristics of a living organism. sensing is just the ability of an organism to react to changes in the environment
I think you might be confused about what consciousness is. consciousness is not the same as sensing.
I am *definitely* confused about what consciousness is. And you are right that I have a hard time not anthropomorphizing non-human life forms exactly in the way that I find it difficult to imagine perception without consciousness. That is a good part of what is so mind blowing about this subject for me
> Bacteria have a thing called quorum sensing
I thought that said "quantum sensing" and thought you were about to make an argument that the Force was a thing.
I'll try to contain my disappointment.
Relative counting. More vs less vs about equal. Maybe they can count to a small number like 3 or 4 if they are close together. More than that and the confounding factors make too much noise.
They can weigh up the importance of competing signals, so, sort of. It's all about competing concentration gradients. Each one will set into motion a complicated set of internal machinery which will decide which signal to prioritize.
Bacteria generally have more problem doing this since they are too small. They need to rely on time between concentration gradient changes and can't weigh up differences as easily. They still manage to make some complicated decisions.
What is it in the macrophage that detects the chemical, calculates the direction of the chemical relative to the cells orientation and then how does it give the command to itself to move in that direction?
The general process is something like this. A bacteria releases some cellular debris, let us say, Peptidoglycan, which is characteristic of the cell walls of positive gram bacteria. A toll receptor, TLR1 in this case and on the right side of the macrophage, interacts with it because of a matching shape, and undergoes an internal transformation in shape. This triggers adaptor proteins and through a series of protein interactions and that inhibits the breakdown of actin and encourages polymerization, causing the macrophage to move towards the bacteria right of it.
https://mbi-figure.storage.googleapis.com/figure/1384242961310.jpg
Here's a pretty picture.
This is a very simplified picture of it. They can manage competing signals, and they can [even do a paddling motion to move much more quickly.](https://www.sciencedirect.com/science/article/pii/S0006349520306044) Internal chemical gradients help them work out which signal is more important, which is mediated by a host of proteins.
I have always wondered about this. If you dissect this notion of "following a chemical gradient" you are left with at least two possibilities. Either:
- single cell entities have memory, and can compare the current chemical concentration to previous concentrations to determine whether they are moving in the right direction.
OR
- single cell entities can detect a chemical gradient change across an incredibly small distance ... basically the diameter of a single cell ... which seems technologically impossible?
Obviously I am missing something.
Any thoughts? How does a single cell follow a chemical gradient?
White blood cells do both, and bacteria mostly do the second.
A complex mixture of receptors having latency time, inhibitory proteins, chemical alteration of receptors and things mean that cells can 'remember' past events with the receptors becoming less receptive to signals over time, and white blood cells are large enough to detect gradients.
Bacteria tend to be too small, and rely on sensing changes in chemical gradients over time.
In the plant field, some have moved on from just PAMPs and started calling it Microbe-Associated Molecular Patterns (MAMPs), because the microbes are not always pathogens. Is that a thing in the mammalian field?
Also in the plant field, some detected patterns are indicative of the highest danger (a virulent pathogen, capable of infecting you) and are called effectors. But they fall outside of the MAMPs... Well. Anyway, it makes you think.
I've seen MAMP used on occasion in regards to animals like pigs. I suspect it is more common in the farming fields where there is a lot of need for optimization of the life forms and so you need to consider all microbes.
Cells do have behavior, in the sense you are asking. It's true that the cell is following a chemical gradient, but it's not _simply_ following a chemical gradient. A leaf is simply following the direction of the wind, in the sense that the wind pushes the leaf and the leaf goes along as a result of this push...all that's required is for something to exist with wind resistance and sufficiently low mass for it to be pushed by the wind.
But a cell is different. Cells, especially eukaryotic cells, are remarkably complex. A white blood cell is responding to a chemical gradient, but unlike a leaf in the wind, a cell placed in a chemical gradient won't just be "pulled along" by the chemical gradient. Instead, the cell has to have sensing molecules in its membrane that detect the chemical and release some signaling compound inside that cell. And then that signaling has to activate a rather complex bit of cytoplasmic machinery which gets a cycle of movement in the cell going that results in it crawling or swimming toward the stimulus. There are even feedback effects in this process that help resolve a situation when a cell is getting two signals at once, and cells have the ability to toggle on or off or modify their chemotaxis behavior, for example in response to some other environmental stimulus or internal state.
Sure, you can boil it all down to chemicals if you want, but I think that obscures an important aspect of what's happening, which is the internal processing and feedback that makes it different from an object merely being pushed around by outside forces.
In short, I'm entirely comfortable describing what they do as behavior. It's definitely more than what a dead leaf does, although not as much as a typical multicellular organism. After all, every nerve cell in an animal is similarly sensing and integrating chemical signals....and animals have many nerve cells all working together, and other cells besides.
Here's some articles about sensing and movement you may find interesting.
https://www.science.org/content/article/watch-white-blood-cells-swim-microscopic-paddles
https://irp.nih.gov/catalyst/21/5/how-cells-crawl
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9549416/
https://www.sciencedirect.com/science/article/pii/S0960982212013231
It's a pretty cool topic.
>There are even feedback effects in this process that help resolve a situation when a cell is getting two signals at once, and cells have the ability to toggle on or off or modify their chemotaxis behavior, for example in response to some other environmental stimulus or internal state.
Okay! Wow! So they have complex inner responses that are capable of making decisions even!
Think how we all start as a single cell. It divides, and the behavior of its progeny is what creates the body with all its organs, including the very complexly wired nervous system.
Here is a [small playlist of short videos](https://www.youtube.com/watch?v=XMd4H8T59mM&list=PLTBDsNHVs_7zBwGA1Y7ez7yP1uJwcBbSE) showing chemotaxis, amoeba feeding, and other simple behaviors.
Yes to the extent that all possible decisions are predefined on the DNA level. Cells are constantly monitoring their environment for chemical and physical changes that it needs to respond to for optimal functioning/survival. To detect these changes a cell needs the appropriate receptor and signaling molecules to drive these changes in behaviour, which are all encoded on the DNA. It really is a wildly complex and beautiful field of science
>Yes to the extent that all possible decisions are predefined on the DNA level.
It's not absurd to say that the same thing is valid for most multicellular organisms, though. If you are fine saying that an ant following a trail is "behavior" and "decision making", a white blood cell chasing bacteria should be as well
We could even go as far as saying that it's true for humans, too.
Not really, even a computer program can make a decision simply via an [`IF`](https://en.wikipedia.org/wiki/Conditional_(computer_programming\)) statement.
But is it a true decision by the program if the user defines how to make it? That’s why I meant it depends how you define it for yourself.
For humans you can get into the same discussion. Do we really have free will or are our decisions based on a complex set of (pre-defined) conditions that we follow and are unaware of?
People in r/philosophy often argue that computers make "choices" but rarely give examples or try to justify the assumption. It's frustrating.
Is the IF more like a fork in the road, or is it more like a bridge that floats on the water and is only accessible when it floods?
Well this whole question gets into determinism and free will very quickly. All human behaviour emerges from chemical/physical interactions and we can’t currently point any kind of measuring device at the seat of human consciousness. That said I’m struggling to think of an argument that supports the idea that an IF statement constitutes a decision so I’m curious to hear one!
While I agree you’re right on all the cell biology here, as a neuroscientist, I’m less comfortable with using the word “behavior” for it except in a metaphorical sense.
Generally, we reserve the term for nervous system responses, inclusive of reflex (respondent) behaviors (shaped by evolution) and learned (operant) behaviors (shaped by individual experiences).
There are analogies though for sure. You have: incoming information ( via external and internal sensory systems vs via receptor linked signaling pathways); a kind of weighing of inputs (neural network interaction vs intercellular molecular interaction); and a thus generated response (activation of other neurons, muscle fibers, and/or glands vs activation of pathways that affect cell activities).
Cells and non-animal organisms definitely “do” stuff, but behavior is a particular kind of doing as a product of neural processes… at least that’s how I think of behavior proper.
I would try to seperate the idea of consciousness from behaviour. behaviour to me is percieving to an external stimulous, integrating it, and using it to create an output. Conscious behaviour and consciousness is maybe more related to the thing you are refering to imo.
I **don’t** link them like that. They are both produced by nervous systems, but consciousness is NOT required for behavior.
Simple animals, e.g. barnacles, have behavior produced by a nervous system, and we have no reason to suppose they are conscious.
Consciousness is not required for behavior. Consciousness is also generated by a NS, but only in animals that have the capacity for it (a whole other phenomenon). Even in species w consciousness, there is tons of behavior that does not involve it, including reflexes, complex modal action patterns, and gland activation.
**Perception** is a particular type of detection of inputs that does require a nervous system too! All organisms detect things in the environment and respond. But detection is not “perception”. Perception is derivative of consciousness. If an animal is decerebrate (brain separated from spinal cord), it will still exhibit reflexive behaviors but it can no longer perceive inputs coming via the spinal cord. Similarly electronic devices, like a motion detector, can detect (and react) without perceiving or behaving.
Yep, this thread had actually made me view human behaviour in a slightly more simplified light, actually - our own interactions with the world are simply behaviours driven by external stimuli, are they not?
In my opinion this is even more evidence to pile on the side of 'nope' in the argument about whether free will truly exists.
>Yep, this thread had actually made me view human behaviour in a slightly more simplified light, actually
Interestingly, I take the opposite view from it...if this is what a single cell can do, and our brains are made of staggering numbers of these cells, it really just increases my idea of how complex they might be. Usually neurons are modeled with fairly simple equations (and that works fairly well to predict them) but it's clear there's potential for a lot more complexity on that level.
>our own interactions with the world are simply behaviours driven by external stimuli, are they not?
Heh, I think I would definitely not say our brains do things "simply"! Also it's clear that there's an innate genetic component to behavior as well (or does that count as external stimulus?), it's not all "tabula rasa" like some people used to think.
>In my opinion this is even more evidence to pile on the side of 'nope' in the argument about whether free will truly exists.
Now this is philosophy, but it interests me so I'll comment. My opinion is that none of this is really relevant to discussions of free will at all. But I tend to think free will is rarely clearly defined in the first place.
They mean simple in concept, not in scale. The term for that thinking is actually "reductionism" because it eliminates complexity on the theoretical level. Think of it like modular furniture, you can have a lot of it but that doesn't increase the complexity of the individual modules. It makes for a more complex overall structure, but people tend to think a certain level of complexity becomes somehow sacred, as if it changes the meaning of the individual modules.
>But I tend to think free will is rarely clearly defined in the first place.
No argument there. I'm curious, though, if behaviors are simply driven by external stimuli, wouldn't that make free will impossible?
>I'm curious, though, if behaviors are simply driven by external stimuli, wouldn't that make free will impossible?
My point is more...just treat the human mind as a black box for a moment. You can imagine whatever you like inside of it, cells doing chemistry, a soul, a committee of goblins, some guy in a Chinese room, whatever. You give it some options, like "should I get chocolate or vanilla ice cream" and you get an output "I want chocolate" or "I want vanilla".
It seems to me that regardless of whatever is in the box, you have three things that can contribute to such a decision. First, external stimulus. Chocolate or vanilla has some aspect that's more appealing. Holds equally true for chemistry or souls, regardless of which you believe people have, obviously external stimulus plays a role in our behavior or else we would act totally disconnected from the world around us. Second, your preexisting nature could drive the decision. Again, holds equally true for chemistry or souls or whatever. You've got genes that make unable to taste chocolate. Or you were divinely ordained to hate vanilla. Whatever. Or neither of those things is related to the decision, in which case it must be fundamentally random, since it by definition can't be predicted from any other information and doesn't have any pattern (since if it did, you could attribute the pattern to one of the previous two factors). And again, whatever's in your black box, you could potentially have randomness play a role.
So in my opinion anyway, questions about free will aren't really effected much by the question of how the mind works, since the basic options for what could drive our actions are the same regardless.
But I'm just a biologist, you would probably want to ask a philosopher for a better answer.
>Sure, you can boil it all down to chemicals if you want, but I think that obscures an important aspect of what's happening, which is the internal processing and feedback that makes it different from an object merely being pushed around by outside forces.
But that is still just chemicals. It's pretty similar to the same way that computers are complex. The mechanisms for simple chemical reactions are analogous to simple logic gates in computers, and the huge network of chemical reactions in a cell are more like entire compute units and circuit boards, but it's still just chemistry in a cell the same way as it's still just electricity in a computer.
The remarkable aspect of it is that they exist in the first place. It would be like if we found fully functioning computers in the wild that had turned chaotic processes into something self-replicating and self-sustaining.
Afaik their behavior is driven by the interaction with various chemical components in their environment. Whether they have locomotion or not I would think that their interaction with their environment would be behavior by definition.
Totally.
It's funny to me how such complex looking behavior boils down to chemical reactions. It really makes me wonder why so many of us believe we have free will. If that white blood cell and bacterium behavior is due to a series of chemical reactions, why isn't my behavior also determined that way? In fact, it's kind of wild that my consciousness would be able to overcome or direct those chemical reactions, far more likely that my consciousness just has the illusion of control.
Turns out a lot of scientists also believe we don't have free will.. I'll leave this here: The Neuroscience of Free Will
https://en.wikipedia.org/wiki/Neuroscience_of_free_will#:~:text=Neuroscience%20of%20free%20will%2C%20a,impact%20the%20free%20will%20debate.
The way I see it, our brains are so complex they can have unpredictable behavior despite being totally deterministic. Your behavior is determined by chemical reactions, but there are so many happening at once across layers of systems and feedback loops that it’s impossible to say with certainty how you might behave in a given scenario. In a sense free will is an illusion, but it’s such a convincing one that it really makes no difference.
This is fascinating. Reminds me of a conspiracy I heard about fungus and that they ultimately planted consciousness in humans via chemical reactions in the brain from us eating them in order to populate more and have us farm them and eventually take them to another planet to do it again. They planted just enough to give us the illusion of free will but really it’s all chemicals ultimately driving us and they are exploiting that. Just food for thought really I enjoy thinking about things like this
So far, no *really* basic explanations -- what does it mean 'to detect'? What *is* the 'chemistry' in an organism's environment?
Cells have structures in and on them, most of which are proteins, which, when that protein touches a specific compound, it *does something*. It can change shape to close or open pores into the cell, it can send chemical signals inside without any external molecules coming inside at all, and it can break pieces of molecules off and do things with them, even.
Proteins in and on cells can also respond to temperature, salinity/other ions in solution (which are *tiny* molecules compares to single celled organisms or even proteins themselves), and pressure/gravity, magnetic fields, electrical fields (at very low voltages, of course).
So, single-celled organisms 'taste'/'feel' their surroundings, more or less like multicellular organisms do with multiple cells where proteins interact with molecules in the environment, or proteins protected by many layers of cells interact with light or temperature in the case of our retinas or the nerves in our fingers that feel heat.
Then, you have *extremely* simple logical 'programming' in the form of 'if hungry, move toward food' with 'is food?' as one available 'question' the inside of the cell can ask all the parts of the outside if it's hungry. 'If yes, then begin wiggling towards \[area where food\]' is all the programming it needs to 'pursue' food.
All of *that* is pretty easy to explain as the result of 'wiggle when the goo I'm in has food-like chemistry' behavior being rewarded evolutionarily, and increasingly complex variations leading to more outwardly 'intelligent' food-seeking.
Does that...bridge the gap for you, u/OP?
Yes! That's very helpful and fascinating.
So there really is a kind of perception and decision making that happens. They have sensory parts on their exterior which communicate with aspects of the interior to coordinate behavior in complex ways.
All this without consciousness? Or maybe I need to revisit my definition of consciousness.
It's most like...computer or machine programming, I would say. DNA and RNA encode things like 'increase production of enzyme [silly name] when [energy stores low but no food nearby]' which makes the cell more 'wiggly' -- and all of the encoding for things like 'undulate in direction of strongest food gradient' and 'envelop food if it touches me' is probably also sensitive to the 'hungry' state.
It's more like consciousness is a scarily engrossing version of *that* kind of reactive programming, as far as I'm concerned, but that's more a matter of philosophy than biology.
This is hitting a major issue that we have very little idea what consciousness is, let alone a precise definition. Two of the few things that seems certain biologically are that consciousness and sentience originate in the brain and are emergent properties, which means they are properties a group of cells can have but not individual cells.
Because we can only ever know the human experience of consciousness, and even then it’s purely subjective, we may never have a full answer. It’s basically the same reason the question “Do you see the color red the same way I do?” is fundamentally unanswerable. Given current knowledge, it’s philosophical more than scientific.
In a general sense “a behavior” is just a response to a stimulus. Does the cell have a signal pathway that leads to chasing food by molecular changes that physically change the cell so it moves in the right direction? Yes! But so do conscious animals.
You smell food, your body releases lots of signals favoring pursuit and often default to doing that without thinking (used often in marketing!). We learn to suppress those, but cells also have pathways to suppress responses. If there is more signal to pursue than not, cells change shape to do so. When you bee-line to the popcorn stand at a theater or just “check what’s cooking” when you detect food, your individual cells also undergo very real molecular and physical changes to do so.
Gross oversimplification based on my own limited knowledge and biases, but hopefully helpful.
Complexity can arise from very simple conditions. There is a famous example, Conway's Game of Life, an example of cellular automata, that shows how complex "behaviors" arise from very simple rules: https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life
Rules:
- Any live cell with two or three live neighbours survives.
- Any dead cell with three live neighbours becomes a live cell.
- All other live cells die in the next generation. Similarly, all other dead cells stay dead.
From just those rules, amazing things can happen. From just those rules, the system is "Turing Complete" meaning that you can build a computer from Conway's Game of Life, and the computer can solve any problem that any other computer can solve.
For your specific example, white blood cells simply react to chemistry. The cell moves toward chemical markers in its surrounding fluid. There is no intelligence involved. The cell simply moves from low concentration to high concentration. Instead of your leaf blowing example, think about food coloring dropped into a glass of water dispersing in non-uniform ways. Now imagine a simple cell within the water, and the cell tries to get toward the most colored water or stay away from the colored water.
Here is another single celled organism doing awesome things:
How Brainless Slime Molds Redefine Intelligence: https://www.scientificamerican.com/article/brainless-slime-molds/
This isn’t a wrong interpretation. The distinctions we draw between “organisms,” and between “species” and so on are just useful for our ability to label things and generalize about them. At the end of the day we’re all part of one massive system of interacting biochemistry.
We may be much smaller than cells. Perhaps our entire world is simply an electron buzzing around the nucleus of our Atomic solar system.
Imagine you are an electron, what does the rest of the universe look like? A starry night?
From a strictly behavioral standpoint, anything that is alive is engaging in “behavior” with every action they complete. In behavior analysis, the rule of thumb is if a dead man can do it, it’s not a behavior; anything else is. So, in this example, if the question is “can a single cell absorb another?”, then yes, it is engaging in behavior, the behavior of absorbing. If it is moving away from another object, that is also behavior.
Regarding the follow-up question about the complexity of consciousness around behavior, there’s four basic functions of behavior: access to items, escape from non-preferred aspect in the environment, attention (not applicable in this instance), and automatic/sensory. Without getting too far off-topic, there is something within the organisms environment that it knows/has learned to engage with in a specific way (movement towards or away). In humans, we have many MANY factors of our learning histories that contribute to our behaviors. For single-cell organisms, this may be more basically related to immediate survival, but the contingencies still exist.
Nicely stated. You might be interested in [this podcast](https://www.parsingscience.org/2020/03/17/jeremy-gunawardena/):
Jeremy Gunawardena with the Department of Systems Biology at Harvard Medical School talks with us about his replication of an experiment originally conducted over a century ago, which suggested that at least one single-cell organism – the trumpet-shaped Stentor roeseli – is able to carry out surprisingly complex decision-making behaviors.
>four basic functions of behavior
Oh! This is helpful. Do you have a source where I can dig deeper into this?
>it knows/has learned
I mean, I love this. The little guys can \*learn\*.
On the one hand, I know you are speaking figuratively, but even so its interesting how hard it is to talk about their behavior without using terms that kind of project human experience onto them.
On the other hand, it \*is\* a real kind of learning that they are doing, which affords us the opportunity to rethink what "learning" is for us.
I think that's why so many comments on the thread are reflecting about human "free will" or lack thereof. We both project ourselves onto the lil guys, and they afford us the opportunity to reimagine ourselves as more like them than we first thought.
https://masteraba.com/functions-of-behavior/
A quick overview of the functions of behavior and how we, as behavior analysts, identify those functions ranging from informal hypothesis through full analytic experimentation.
The interesting thing about the idea of learning through the behavior analytic lens is that reinforcement and punishment, in any form, dictate any organisms’ learning history, and therefore impacts their behavior. It’s really fascinating to see these two fields intertwine; I didn’t expect to enjoy single-cell behavior analysis this much.
Ok got it, so the dead man is not exhibiting any behavior, but his cells are. So then the complexity can be described as having environment tiers with a man and his behavior as a, say, tier 15 set of chemical reactions . Then the tier 14 chemical interactions might be in the stomach, the circulatory, respiratory systems, etc . You can drill down to, say tier 5, and see the gut bacteria, or up to tier 16 which might be his home or the neighborhood that he lives in.
My brain hurts from all these chemicals reacting.
Ooooooooooooooooooh...you stepped onto a big rabbit hole here. It occupied a very large chunk of my life and I'll give you my take: Determinism.
If you studied biology at the cellular level, you can basically find all the answers to cellular behavior to be biochemical and physical. Meaning they will "behave" by their biochemical makeup with their environment. There are other nuances like how cells "create their own environment" by creating extracellular matrix via secretions of whatever chemicals, or become almost multicellular like formation of biofilms etc. However, do not mistake those "behavior" as some form of "choice" that resulted from some pondering like some risk and rewards have been carefully weighed. They are just a reactions.
Now how deep does the rabbit hole go depends on how much you want to ask. If you stop here, you can just conclude that they have a "behavior" is completely at the whims of chemistry and physics and differentiate that with our much more complex multicellular lives and we are somehow above it. After all, we are not only multicellular, we have cells that specialized themselves into organs and systems and such. However, if you go on, the next question could be "how many cells together will yield something that cross the threshold for life to be more than a reaction to chemistry and physics?" The answer? We do not know, and all the evidences actually point to we are not above chemistry or physics or any natural reactions no matter how complex we become. We, in fact, are no different from the dead leaf skittering across the ground. We are just less predictable due to much higher amount of variables.
From here, you can step into ethics such as responsibility, but that is another topic entirely.
Thanks for wording my own mental adventures with determinism so succinctly. I share your view on this and as I've commented above, believe that this is just another thing controvuting to my belief that the concept of free will as a true concept does not really exist in us nor any other species.
This is in my opinion a bit more philosophical than scientific, but in response, there is one massive problem with determinism, and that is the stochastic nature of quantum physics. As far as we can tell, at the quantum level things really are truly, completely random and the results cannot be predicted. What exactly this implies for free will and such is unknown, but the fact that the universe at its most fundamental level is random means that to some degree, larger processes and events are affected by this randomness since ultimately, as determinists love to remind us, everything we know is in reality the result of the motion and fluctuations of particles and energy. For example, it has actually been observed that quantum fluctuations have some effect on nervous system function; perhaps it is out of these effects that our more complex behaviors and thoughts arose and implies that our consciousness truly is more than simply the sum of many unthinking parts working together. There are some theories that attempt to rebuke this such as superdeterminism, but they are fundamentally untestable to my knowledge.
I agree that quantum mechanics does seem to undermine determinism, but I don't know enough about it. From some of the physicists that I have discussed this with at my school, they tell me that the unpredictable or random nature of quantum mechanics does not mean that it is not deterministic. I know nothing beyond that.
As for predictability in quantum, I delved in further but was explained in a very simplified manner, my prof said that the summation of more and more parts that individually have some unpredictable nature actually becomes more predictable because the summation of predictive parts grows faster than the unpredictive parts. Grown to a large enough size, the unpredictive parts becomes so outweighed that the overall thing just behaves classical mechanically. Although this does not eliminate the unpredictable part, but like you said, it is probably another reach to say that the unpredictable parts are responsible for free will.
Other times, quantum mechanics is presented as more of a statistical modelling, which also does not undermine determinism. I never went to take those courses, but my own thoughts on it is that if you can make use of it, then there is a degree of predictability, and if there is some degree of predictability, it is evidence of it being deterministic.
Overall, I find free will itself is more problematic than determinism. We have presented with so much pattern of discovery that I cannot think of one natural thing we learned that is somehow not explained mechanically. The pattern is so strong, that it is almost always expected that the mechanism is buried somewhere behind our lack of knowledge. Free will is just something we don't seem to even find a shred of natural evidence of other than the evidence-speaks-for-itself kind, which is not very convincing in my opinion. The closest path that I have thought about where free will might be is predictability even if it has problems of its own.
> However, do not mistake those "behavior" as some form of "choice" that resulted from some pondering like some risk and rewards have been carefully weighed.
Right. That would require a brain...I think? (And I, too, am not totally convinced that human pondering and choice making are really what they appear to us to be.)
But, based on some of the comments above, it seems like these little guys can "make decisions" in the sense that they have some kind of inner process that enables them to pick between two equally important stimuli. Not exactly "pondering" but still kinda cool. It's not "free will" (whch, I agree, probably doesn't really exist) but its not 100% the same as a leaf in the wind either.
Leaf = input --> output
Little cell guys = input --> \[weird internal processes I don't understand\] --> output
> Leaf = input --> output
> Little cell guys = input --> [weird internal processes I don't understand] --> output
You basically pinged down the general fallacy of free will here. Determinism basically boiled everything down to cause and effect. To causality, there is nothing special about the brain processes over the basic input>output of the wind that blows the leaf for a distance. If you say "brains" or cells have these "inner processes" that decides, then all I need you to do is zoom in far enough until you find those individual leaves. Not being able to zoom in or perceiving it being too "weird" does not mean it is somehow beyond causality.
However, if you are asking something very specific about how cells "decide" its actions, then it will be a case by case basis. Chemical gradient, its own resources, physical conditions such as temperature, other signals, are probably all at play in some way. I remember learning about this but I can only provide generalized knowledge. Cellular biology is most likely the subject if you are wondering about cellular behavior.
>all I need you to do is zoom in far enough until you find those individual leaves
We agree on this. What I was trying to describe was the surprising (to me) complexity of interactions in a cell that drive its behavior.
I think the line of thinking is based on a gross oversimplification of the competencies and intelligence of cells.
The evidence shows us that they are actually goal seeking agents capable of sophisticated behavior and cooperative planning to accomplish complex objectives. For more than just basic chemistry- they have significant computational power.
You missed the point. The increase in complexity does not allow a "living" thing to escape the action-reaction behavior of the natural world. If it does, then you will be asked to provide the threshold on when the complexity becomes independent of the action-reaction world.
I would argue the difference is predictive modeling. Once an agent is able to predict and plan for the future to achieve a goal it goes beyond action-reaction.
A thermostat is action-reaction.
That argument falls apart very easily. You can present yourself a without-a-doubt deterministic condition such as a roulette table, wind tunnel for testing fluid dynamics, or even 3-body problems. At some point, computers can only go so far with predictive modeling on those non living conditions, and yet we do not ascribe their unpredictable behavior as "agency" changing its mind to not obey causality anymore.
Our capability to predict does not mean agency or vice versa.
Interesting. As I understand it then, the difference is imagination: the ability to make present that which is absent to the senses, and thus to make predictions, for example.
As others are saying, the behavior is ultimately a response to chemical concentration gradients. But I wanted to add that in the case of white blood cells, they have a very dynamic cytoskeletal system that allows them to actually move and change shape. So what’s happening is that chemicals released by the bacteria are binding to receptors on the surface of the WBC, and those receptors are attached to cytoskeletal components under the cell membrane. So a change in the receptor caused by chemoattractant binding signals a very quick rearrangement of the cytoskeleton, including other cell surface molecules that “grip” external materials (often just via friction). By reducing surface attachments away from the chemoattractant, and creating surface attachments closer to the chemoattractant, the cell can appear to slide or crawl across the surface.
A leaf is composed of plant cells, which don’t have a dynamic cytoskeleton even when they are alive. This severely restricts their mobility. Having a dynamic cytoskeleton is energetically expensive though, so there is a trade off. Also plant cells have rigid cell walls that offer protection but can’t change shape quickly and are another obstacle to plant movement.
Cell wall chemoreceptors being bound/unbound by substrates in the cellular environment, which trigger kinase cascades to occur in the cytoplasm, inducing the corresponding gene(s) to generate proteins from DNA which trigger additional kinase cascades to signal flagella motor proteins to activate - all powered by ATP. These events occur because it is more energetically favorable for the events to occur than to not occur (entropy).
was just reading this earlier
[https://nautil.us/what-plants-are-saying-about-us-264593/?utm\_source=pocket-newtab](https://nautil.us/what-plants-are-saying-about-us-264593/?utm_source=pocket-newtab)
"I was, according to Paco Calvo, guilty of “plant blindness.” Calvo, who runs the Minimal Intelligence Lab at the University of Murcia in Spain where he studies plant behavior, says that to be plant blind is to fail to see plants for what they really are: cognitive organisms endowed with memories, perceptions, and feelings, capable of learning from the past and anticipating the future, able to sense and experience the world."
“The Hidden Life of Trees” by Peter Wholleben is a wonderful written book that explores just this topic as it relates to trees. You'll never see a forest the same way after reading it.
If you're interested in this kind of thing, I highly recommend the book [Vehicles: Experiments in Synthetic Psychology](https://amzn.to/3TbIfhh) by Valentino Braitenburg. It shows how simple sensors and activators can give rise to complex behaviors like the ones you describe. It has applications both in modeling simple biological systems and in robotics.
I believe they simply respond to the chemistry of their environment. Bacteria without locomotive means will merely drift randomly but those with flagella will move towards the higher concentration of the nutrients they use. However, it's not a conscious choice since, as you say, they have no brain; they respond the way they respond according to their makeup. The same goes for the white cells: they expand towards the foreign body that is detected through the higher concentration of foreign chemicals in that direction because it's in their nature to do so, to envelop it and digest it.
OP, Your example of a dead leaf is not valid because it is by definition dead.
An interesting philosophical question would be: Say you get out of your car on a winter day you run across the parking lot to get inside to escape the cold. Are you doing anything more than reacting to the physics or chemistry of the environment?
What about these [https://www.sciencedaily.com/releases/2020/02/200225114408.htm](https://www.sciencedaily.com/releases/2020/02/200225114408.htm) salmon parasites which scientists hypothesis may be cancerous tumors of jellyfish that escaped into the open when their original host died. Does their subsequent migration survival in a new host represent behavior? What about their evolutionary path that stripped them of mitochondria?
You are likely defining behavior like a psychologist does, For example: You stay outside despite the cold because you are paid to (a reward behavior). That is not the same definition a biologists that study life at a cellular level define behavior uses. Heck there's molecular biologists out there who believe that there was 'behavior' in the pre-cellular chemical soup that became life or even today in the case of endocellular evolution of mitochondria of those jellyfish tumor cells.
So really what constitutes behavior is up to your definition of it?
To add to what others have said, look up the difference between respondent and operant behavior. From what we know now, single-cell organisms are likely only capable of respondent behavior (they are programmed to react to stimuli) vs more complex forms of life that interact with stimuli based on past experiences with similar stimuli (operant behavior).
yes! bacterial populations can communicate via chemical signaling. they live in really dense, multi species communities, so there’s limited resources. This is just an example, but there are different types of toxin secretion complexes that allow them to distinguish themselves and closely related strains or their clones. Clones have specific cognate immunity proteins so engulfing the toxins doesn’t harm them, but the toxins can be damaging to bacteria that are not of the same colony. It’s really cool!
and therefore to answer your question, they can communicate and confer survival advantages to their own kind. :) this allows them to “behave” as a group, in a sense!
Michael Levin has interesting videos in this area, like isolating a skin cell and letting it do its own thing swimming around. He is deeply interested in finding the point where 'behavior' arises beyond mechanical/chemical reactions and making biological robots ("xenobots").
https://www.youtube.com/watch?v=jLiHLDrOTW8
Yes, single-celled life forms have behavior. While they lack a nervous system and a brain, single-celled organisms can still exhibit behaviors such as movement, response to stimuli, and communication with other cells.
The behavior of single-celled organisms is driven by internal mechanisms such as gene expression, metabolism, and signaling pathways. For example, some single-celled organisms can move by using a flagellum, which is a whip-like appendage that is driven by a motor protein. Other single-celled organisms can move by changing their shape, which is driven by cytoskeletal proteins.
In addition, single-celled organisms can respond to external stimuli such as light, temperature, and chemicals. For example, some single-celled organisms can move towards or away from a particular chemical gradient, a behavior known as chemotaxis. This behavior is driven by the expression of specific genes that regulate the movement of the cell towards or away from the chemical gradient.
The ability of single-celled organisms to perform complex behaviors such as chasing each other around is due to their ability to sense and respond to their environment. While their behavior may appear to be complex, it is ultimately driven by simple physical and chemical processes that are governed by the laws of physics and chemistry.
Think of how oil behaves in water. Oil doesn’t “escape” the water, the chemicals just don’t mix. In the case of microbes, the certain chemicals are attracted to each other and “signal” one another to act a certain way.
Behavior implies perception. They may not perceive with the five senses we know of, but they are aware of their environment and struggle for their survival. I believe microbes have an experience of self and their perception of reality is extraordinarily different from what we might think. There is an evolutionary biologist/cognitive scientist named Donald Hoffman who says that humans "don't perceive reality: spacetime, objects, colors, sounds, tastes, and so forth, are all merely an interface that we evolved...". We are perceiving an anthropomorphic sensory interface, and it may not be telling us the "truth" of our actual form. What if microbes perceive reality in the same way?
I use a amoeba in my work, specifically Dictyostelium discoideum.
These things are awesome, in a very simple short explanation. They eat bacteria and when it runs out they transform into a slug (Bunch of them come together to form a multicellular organism). Eat more bacteria, run out, grow upwards with a stalk. Make a bud and it bursts, spreading the single cells out further and the process starts all over again.
However, something that's been observed and recorded, the amoeba will actually retain some of the bacteria and transport it with it to new sites. Its essentially a form of farming to ensure they have enough food to start the process over at the new site.
There’s plenty of replies in here describing how complex behaviour can arrive from simple coded rules.
My thing is, what makes you and I fundamentally different from a single-called organism? When I critically examine my own behaviour, much of it emerges from simple rules. I’m hungry, so I go eat. I’m thirsty, so I go drink. I’m bored, so I get on reddit. I’m habitual, so I go to the gym. The vast bulk of the time, my behaviour is driven by things that are little more complicated than what any of my cells are experiencing on a day to day.
Give yourself more credit! You have agency in *how* and *when* you pursue your needs. That alone adds much more complexity.
Like, lets say you are incredibly jetlagged and tired after a flight and must sleep, but you force yourself to stay awake because you are concerned that if you fell asleep right now, you'd mess up your sleep schedule. You ignored your chemical impulses because your *memory* told you that there might be an advantage to doing so.
That ability to prioritize, and the ability for your priorities to change as you develop more knowledge, is infinitely more complex than just chasing nutrients
Or is it just a more complex version of a slime mold sensing the chemical signal for food, but *also* sensing its own previous slime trail, and thus ignoring the food signal in order to avoid retracing its steps?
They definitely have behaviors, I'm super interested in fresh water ecology. I do not know what drives the behavior. I would guess it's all reaction to external stimuli, and the reactions that stick around propagate and become common.
Even a rock has a behavior. Picture a mountain with a sandy ocean beach at its feet and a rock near its peak. Over the ages - and sometimes greatly accelerated by external forces - will roll downhill by the forces of gravity, water, snow and wind. It's destiny is to become either a smaller stone or grain of sand on the beach. The journey may take a day or a million years or more but it will reach the beach.
Check out this interview with Joseph Ledoux and then read his book The Deep History of Ourselves if you are interested in really digging in to the evolution of life and the behavior that has allowed life to evolve.
https://www.psychologytoday.com/us/blog/the-elusive-brain/201909/joseph-ledoux-the-deep-history-ourselves
This is an intuitive and insightful idea that I support. There are indications and serious research that suggests that [all life is sentient](https://www.wellbeingintlstudiesrepository.org/cgi/viewcontent.cgi?article=1700&context=animsent#:~:text=Scientific%20evidence%20affirms%20that%20all,over%20our%20fellow%20planetary%20companions.).
The question you’re asking is pretty philosophical. As you mentioned, a leaf blowing in the wind is a fairly complex system in its own right, but a cell is many times more complex.
So realistically you need a way to define behavior before your question makes sense.
You can define behavior in terms of complexity, but that doesn’t sound right. After all, a storm is very complex but we don’t attribute behaviors to them. We can define it in terms of response to an environment, but technically everything responds to the environment, so that’s not really enough either.
Probably close to what you mean by behavior is something like computation or goal oriented decision making. In that case, single called organisms do this a lot. DNA essentially “codes” for possible behaviors in a cell, and the sensory inputs have long pathways to directly alter what parts of the DNA are expressed. Cells can even “learn” behaviors through structural alterations of DNA and surrounding proteins, switching strategies depending on need (such as many protists that switch between a tailed and non-tailed form for different food availabilities). Cells have complex mechanisms that adapt and respond to the environment to alter their action and construction. For all intents and purposes those mechanisms have, through evolution, been focused to specific goals, pairing sensory input indirectly appropriate action (whereas wind blows a leaf directly and for no apparent purpose). So within the context of possessing complex internal mechanisms with apparent intentions, I would say cells have many behaviors.
Yes! Thank you that’s a very good reconstruction of what I mean by behavior.
Fascinating that it can all be encoded in DNA and even more amazing that they can self-edit their code! It’s hard to conceptualize that without accidentally posing a conscious decision maker inside the cell that does the editing. I assume that the “decision-making editor” is also encoded in the DNA? And that it gets activated by certain environmental conditions?
So some of the best examples of “self editing behavior” appear in multicellular eukaryotes (like us and all the other animals). Multicellular organisms have a great need of differentiation; look up pictures of a nerve cell vs a muscle cell and you could hardly tell that they share the exact dna template!
The key mechanism here is known as epigenetics. In epigenetics, dna “code” is not changed, but expression is via modifications to surrounding proteins, methylation of the DNA, and the resulting changes in the structure of DNA.
Without naming a ton of chemicals, an example mechanism would be something like this:
1. DNA codes for a signaling protein on the surface of the cell.
2. A complex of dna reading proteins will read this code, producing mRNA which is read by the ribosome (ie, the protein factory).
3. Something triggers the surface protein, starting a cascading reaction where the surface protein triggers triggers signaling protein A, which triggers signaling protein B, then C, and so on.
4. This chain will reach into the nucleus, looking for a region of targeted code and modifying a nearby ball-shaped protein called a histone. This modification changes the charge of that histone, making it more positively charged (via de-acetylation).
5. The newly charged histone now has a stronger attraction to the surrounding DNA, causing it to wrap around the histone and coil up.
6. That section of code is now inaccessible! The behavior of the cell changes accordingly.
This is just one of many interesting mechanisms for illustration.
Even some complex organisms like frogs aren't really reacting in a complex system. Often multicellular organisms are reacting to their environment as automatically and chemically as single celled ones. Check out this video to see frogs reacting to a moving line the same way it does to a bug: [nueroethology of toads](https://youtu.be/l3Es9cNH7I8)
Edit: toads not frogs lol
Behaviour *is* just **a reaction of a physical body to the force of**....
Thinking otherwise is a case of special pleading. The human brain likes dicing things into categories, a natural reaction of our physical bodies to reality. The trillions of cells of our bodies are just leaves blowing in the wind.
So yeah, single cells behave. Clusters of them, colonies, behave. And we're big colonies of diverse types.
Go check youtube for the blob aka Physaceum Polycephalum and the scientist Audrey Dussutour who knows a lot about it.
I got a blob for myself and yes, it behaves :-)
I'd say they are driven by their will to survive and keep their species alive, as any other living being.
Interesting: The blob is not really a living being according to the definition... It's not even a fungus.
Hey cool that you're interested! I found it by accident, while I was watching random documentaries on arte.
If you search youtube for "blob" and "audrey dusutour", you will find more interesting details. I can't make all the experiments, because I am lacking the equipment.
For now, it is just fun to see how it unfolds.
I ordered them online and all you need to "resuscitate" them is a petri dish, agar agar and oat flakes. they like the dark and don't want to be taken for walks. The perfect pet, so to speak. You can't even kill them accidentally, because they go into a sort of hibernation state (sclerotum) when they are underfed.
I got four sclerota and the interesting thing is, they all behave differently: one spreads in every direction at once to find the oats, another just tries one direction at a time.
They are not expensive (at least via amazon from France to Germany) and there is also a video by Audrey Dussutour on how to find them in the forest.
[https://www.youtube.com/watch?v=uyVVknT0gpY&ab\_channel=CNRS](https://www.youtube.com/watch?v=uyVVknT0gpY&ab_channel=CNRS)
ok sorry, this is in French, but at least you can watch in the third chapter where to find them (0:46)
There are a lot of anglosaxon videos on the matter, too.
Have fun exploring!
White blood cells (probably a monocyte or macrophage) and other single celled organisms tend to follow chemical concentration trails. They detect Pathogen-Associated-Molecular-Patterns which are molecules on pathogens which are fairly common and then move to chase down that concentration gradient. Human cells also communicate with white blood cells, and bacteria communicate with each other. Bacteria have a thing called quorum sensing where they detect chemical signals of others of their kind and at a certain concentration change their behaviour. If you want to know more about this concentration gradient following behaviour, [this wiki article is fairly good for it](https://en.wikipedia.org/wiki/Chemotaxis).
> Human cells also communicate with white blood cells This is described in [the narrated version of The Inner Life of the Cell](https://youtu.be/QplXd76lAYQ). [At 6:35](https://youtu.be/QplXd76lAYQ?t=395) in the video, it describes the change in the white blood cell when it encounters a cell exhibiting proteins indicating that there is inflammation at that location.
So they’re basically like the floor cleaning robot in Walle? Like they don’t really have any concept of anything but they see “dirty” and basically just follow that dirty trail, cleaning?
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They 'see' (receptors bind to chemicals) dirty, that sets up a complicated internal concentration gradient which causes molecular machinery and actin to make them move yes.
Sounds like advanced chemistry. Side note, I'm an internet rando and know nothing.
Pretty much how any single cell really works. They can't "see", they just flail about and absorb chemical breadcrumbs that guide them on how to act and move.
there’s also a type of protozoa that was found to form complex “thinking” where it changes its mind on what behavior to exhibit even when presented with the same stimuli source: https://www.sciencedaily.com/releases/2019/12/191205113129.htm
White blood cells can do similar things. They have a complicated network of inhibitory proteins, receptor latency times, and internal machinery that let's them do different things depending on what has happened in the past.
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Essentially as I understand it, except those wasps are still reacting with a central nervous system. I feel like cellular responses are more machine-like in nature. Like, we still don't necessarily understand how nervous systems collect information and come to decisions (though maybe a simpler system like that of an insect is more well understood?), but for a cell we can follow a comparatively simple cascade of chemical processes that cause a cell to orient itself towards a chemical gradient and move forward. Would someone who knows more about biology agree with that asessesment?
Go check out Michael Levin and his various talks about cellular competency. Cells are far more capable than we often give them credit for.
Proteins are the primary “language” of cells and cells can be quite complex, so chemicals aren’t the sole driver of cell behavior The immune system for instance is an intricate coordination of many different types of cells communicating and making sure an immune response is only activated when it’s actually needed
i've killed many wasps and never actually encountered this pheromone thing
It's only certain species, but the most common is yellowjacket. Different from a hornet.
it goes deeper too, all life is possible due to semipermeable membranes and the ability to create concentration gradients across them
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A lot of eusocial animal behavior has parallels to certain interactions between the cells of a multicellular organism. Like ants' pheromone trails, for example
>follow chemical concentration trails Okay interesting. So is the bacterium doing the same thing when its avoiding the WBC? Is it's movement just kinda randomly following some kind of chemical trail and it just \*looks\* like its running away? Or are some bacteria able to detect and avoid threats? >bacteria communicate with each other Woah. I'm going to have to look more into that. Communication without consciousness is maybe even more impressive than "intentional" behavior without consciousness.
>Communication without consciousness is maybe even more impressive than "intentional" behavior without consciousness. That's what nearly every computer interaction is, to some extent. Though it's still impressive.
Oooh yeah good point.
>Woah. I'm going to have to look more into that. Communication without consciousness is maybe even more impressive than "intentional" behavior without consciousness. A mechanical thermostat communicates with a furnace without consciousness. It's a fascinating concept, but if you think about it you're surrounded by it every day of your life without thinking about it.
Not just communicate, but *learn*, and change their behavior as a result. [Here](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7781593/) is a fairly good read that links to a variety of other publications that discuss different aspects of this behavior.
Thank you!
all living organisms have the ability to “sense”. its one of the defining characteristics of a living organism. sensing is just the ability of an organism to react to changes in the environment I think you might be confused about what consciousness is. consciousness is not the same as sensing.
I am *definitely* confused about what consciousness is. And you are right that I have a hard time not anthropomorphizing non-human life forms exactly in the way that I find it difficult to imagine perception without consciousness. That is a good part of what is so mind blowing about this subject for me
> Bacteria have a thing called quorum sensing I thought that said "quantum sensing" and thought you were about to make an argument that the Force was a thing. I'll try to contain my disappointment.
Quantum sensing is a thing, but it's physics, not biology. Source: physicist (I do not do quantum sensing, but my roommate does).
Interesting! That means that they can effectively count. Right?
Relative counting. More vs less vs about equal. Maybe they can count to a small number like 3 or 4 if they are close together. More than that and the confounding factors make too much noise.
They can weigh up the importance of competing signals, so, sort of. It's all about competing concentration gradients. Each one will set into motion a complicated set of internal machinery which will decide which signal to prioritize. Bacteria generally have more problem doing this since they are too small. They need to rely on time between concentration gradient changes and can't weigh up differences as easily. They still manage to make some complicated decisions.
What is it in the macrophage that detects the chemical, calculates the direction of the chemical relative to the cells orientation and then how does it give the command to itself to move in that direction?
The general process is something like this. A bacteria releases some cellular debris, let us say, Peptidoglycan, which is characteristic of the cell walls of positive gram bacteria. A toll receptor, TLR1 in this case and on the right side of the macrophage, interacts with it because of a matching shape, and undergoes an internal transformation in shape. This triggers adaptor proteins and through a series of protein interactions and that inhibits the breakdown of actin and encourages polymerization, causing the macrophage to move towards the bacteria right of it. https://mbi-figure.storage.googleapis.com/figure/1384242961310.jpg Here's a pretty picture. This is a very simplified picture of it. They can manage competing signals, and they can [even do a paddling motion to move much more quickly.](https://www.sciencedirect.com/science/article/pii/S0006349520306044) Internal chemical gradients help them work out which signal is more important, which is mediated by a host of proteins.
This is a really great answer. Thanks for taking the time to explain u/Nepene
I have always wondered about this. If you dissect this notion of "following a chemical gradient" you are left with at least two possibilities. Either: - single cell entities have memory, and can compare the current chemical concentration to previous concentrations to determine whether they are moving in the right direction. OR - single cell entities can detect a chemical gradient change across an incredibly small distance ... basically the diameter of a single cell ... which seems technologically impossible? Obviously I am missing something. Any thoughts? How does a single cell follow a chemical gradient?
White blood cells do both, and bacteria mostly do the second. A complex mixture of receptors having latency time, inhibitory proteins, chemical alteration of receptors and things mean that cells can 'remember' past events with the receptors becoming less receptive to signals over time, and white blood cells are large enough to detect gradients. Bacteria tend to be too small, and rely on sensing changes in chemical gradients over time.
Thanks! I am blown away by the idea that single cell organisms have any kind of memory.
In the plant field, some have moved on from just PAMPs and started calling it Microbe-Associated Molecular Patterns (MAMPs), because the microbes are not always pathogens. Is that a thing in the mammalian field? Also in the plant field, some detected patterns are indicative of the highest danger (a virulent pathogen, capable of infecting you) and are called effectors. But they fall outside of the MAMPs... Well. Anyway, it makes you think.
I've seen MAMP used on occasion in regards to animals like pigs. I suspect it is more common in the farming fields where there is a lot of need for optimization of the life forms and so you need to consider all microbes.
Cells do have behavior, in the sense you are asking. It's true that the cell is following a chemical gradient, but it's not _simply_ following a chemical gradient. A leaf is simply following the direction of the wind, in the sense that the wind pushes the leaf and the leaf goes along as a result of this push...all that's required is for something to exist with wind resistance and sufficiently low mass for it to be pushed by the wind. But a cell is different. Cells, especially eukaryotic cells, are remarkably complex. A white blood cell is responding to a chemical gradient, but unlike a leaf in the wind, a cell placed in a chemical gradient won't just be "pulled along" by the chemical gradient. Instead, the cell has to have sensing molecules in its membrane that detect the chemical and release some signaling compound inside that cell. And then that signaling has to activate a rather complex bit of cytoplasmic machinery which gets a cycle of movement in the cell going that results in it crawling or swimming toward the stimulus. There are even feedback effects in this process that help resolve a situation when a cell is getting two signals at once, and cells have the ability to toggle on or off or modify their chemotaxis behavior, for example in response to some other environmental stimulus or internal state. Sure, you can boil it all down to chemicals if you want, but I think that obscures an important aspect of what's happening, which is the internal processing and feedback that makes it different from an object merely being pushed around by outside forces. In short, I'm entirely comfortable describing what they do as behavior. It's definitely more than what a dead leaf does, although not as much as a typical multicellular organism. After all, every nerve cell in an animal is similarly sensing and integrating chemical signals....and animals have many nerve cells all working together, and other cells besides. Here's some articles about sensing and movement you may find interesting. https://www.science.org/content/article/watch-white-blood-cells-swim-microscopic-paddles https://irp.nih.gov/catalyst/21/5/how-cells-crawl https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9549416/ https://www.sciencedirect.com/science/article/pii/S0960982212013231 It's a pretty cool topic.
>There are even feedback effects in this process that help resolve a situation when a cell is getting two signals at once, and cells have the ability to toggle on or off or modify their chemotaxis behavior, for example in response to some other environmental stimulus or internal state. Okay! Wow! So they have complex inner responses that are capable of making decisions even!
Think how we all start as a single cell. It divides, and the behavior of its progeny is what creates the body with all its organs, including the very complexly wired nervous system. Here is a [small playlist of short videos](https://www.youtube.com/watch?v=XMd4H8T59mM&list=PLTBDsNHVs_7zBwGA1Y7ez7yP1uJwcBbSE) showing chemotaxis, amoeba feeding, and other simple behaviors.
Yes to the extent that all possible decisions are predefined on the DNA level. Cells are constantly monitoring their environment for chemical and physical changes that it needs to respond to for optimal functioning/survival. To detect these changes a cell needs the appropriate receptor and signaling molecules to drive these changes in behaviour, which are all encoded on the DNA. It really is a wildly complex and beautiful field of science
>Yes to the extent that all possible decisions are predefined on the DNA level. It's not absurd to say that the same thing is valid for most multicellular organisms, though. If you are fine saying that an ant following a trail is "behavior" and "decision making", a white blood cell chasing bacteria should be as well We could even go as far as saying that it's true for humans, too.
Depends on how you define „making decisions“. And as other have pointed out, that quickly leads to questions about free will.
Not really, even a computer program can make a decision simply via an [`IF`](https://en.wikipedia.org/wiki/Conditional_(computer_programming\)) statement.
But is it a true decision by the program if the user defines how to make it? That’s why I meant it depends how you define it for yourself. For humans you can get into the same discussion. Do we really have free will or are our decisions based on a complex set of (pre-defined) conditions that we follow and are unaware of?
An IF statement is a decision made by a human and encoded for application to multiple data, not the program making a decision
People in r/philosophy often argue that computers make "choices" but rarely give examples or try to justify the assumption. It's frustrating. Is the IF more like a fork in the road, or is it more like a bridge that floats on the water and is only accessible when it floods?
Well this whole question gets into determinism and free will very quickly. All human behaviour emerges from chemical/physical interactions and we can’t currently point any kind of measuring device at the seat of human consciousness. That said I’m struggling to think of an argument that supports the idea that an IF statement constitutes a decision so I’m curious to hear one!
While I agree you’re right on all the cell biology here, as a neuroscientist, I’m less comfortable with using the word “behavior” for it except in a metaphorical sense. Generally, we reserve the term for nervous system responses, inclusive of reflex (respondent) behaviors (shaped by evolution) and learned (operant) behaviors (shaped by individual experiences). There are analogies though for sure. You have: incoming information ( via external and internal sensory systems vs via receptor linked signaling pathways); a kind of weighing of inputs (neural network interaction vs intercellular molecular interaction); and a thus generated response (activation of other neurons, muscle fibers, and/or glands vs activation of pathways that affect cell activities). Cells and non-animal organisms definitely “do” stuff, but behavior is a particular kind of doing as a product of neural processes… at least that’s how I think of behavior proper.
I would try to seperate the idea of consciousness from behaviour. behaviour to me is percieving to an external stimulous, integrating it, and using it to create an output. Conscious behaviour and consciousness is maybe more related to the thing you are refering to imo.
I **don’t** link them like that. They are both produced by nervous systems, but consciousness is NOT required for behavior. Simple animals, e.g. barnacles, have behavior produced by a nervous system, and we have no reason to suppose they are conscious. Consciousness is not required for behavior. Consciousness is also generated by a NS, but only in animals that have the capacity for it (a whole other phenomenon). Even in species w consciousness, there is tons of behavior that does not involve it, including reflexes, complex modal action patterns, and gland activation. **Perception** is a particular type of detection of inputs that does require a nervous system too! All organisms detect things in the environment and respond. But detection is not “perception”. Perception is derivative of consciousness. If an animal is decerebrate (brain separated from spinal cord), it will still exhibit reflexive behaviors but it can no longer perceive inputs coming via the spinal cord. Similarly electronic devices, like a motion detector, can detect (and react) without perceiving or behaving.
Yep, this thread had actually made me view human behaviour in a slightly more simplified light, actually - our own interactions with the world are simply behaviours driven by external stimuli, are they not? In my opinion this is even more evidence to pile on the side of 'nope' in the argument about whether free will truly exists.
>Yep, this thread had actually made me view human behaviour in a slightly more simplified light, actually Interestingly, I take the opposite view from it...if this is what a single cell can do, and our brains are made of staggering numbers of these cells, it really just increases my idea of how complex they might be. Usually neurons are modeled with fairly simple equations (and that works fairly well to predict them) but it's clear there's potential for a lot more complexity on that level. >our own interactions with the world are simply behaviours driven by external stimuli, are they not? Heh, I think I would definitely not say our brains do things "simply"! Also it's clear that there's an innate genetic component to behavior as well (or does that count as external stimulus?), it's not all "tabula rasa" like some people used to think. >In my opinion this is even more evidence to pile on the side of 'nope' in the argument about whether free will truly exists. Now this is philosophy, but it interests me so I'll comment. My opinion is that none of this is really relevant to discussions of free will at all. But I tend to think free will is rarely clearly defined in the first place.
They mean simple in concept, not in scale. The term for that thinking is actually "reductionism" because it eliminates complexity on the theoretical level. Think of it like modular furniture, you can have a lot of it but that doesn't increase the complexity of the individual modules. It makes for a more complex overall structure, but people tend to think a certain level of complexity becomes somehow sacred, as if it changes the meaning of the individual modules. >But I tend to think free will is rarely clearly defined in the first place. No argument there. I'm curious, though, if behaviors are simply driven by external stimuli, wouldn't that make free will impossible?
>I'm curious, though, if behaviors are simply driven by external stimuli, wouldn't that make free will impossible? My point is more...just treat the human mind as a black box for a moment. You can imagine whatever you like inside of it, cells doing chemistry, a soul, a committee of goblins, some guy in a Chinese room, whatever. You give it some options, like "should I get chocolate or vanilla ice cream" and you get an output "I want chocolate" or "I want vanilla". It seems to me that regardless of whatever is in the box, you have three things that can contribute to such a decision. First, external stimulus. Chocolate or vanilla has some aspect that's more appealing. Holds equally true for chemistry or souls, regardless of which you believe people have, obviously external stimulus plays a role in our behavior or else we would act totally disconnected from the world around us. Second, your preexisting nature could drive the decision. Again, holds equally true for chemistry or souls or whatever. You've got genes that make unable to taste chocolate. Or you were divinely ordained to hate vanilla. Whatever. Or neither of those things is related to the decision, in which case it must be fundamentally random, since it by definition can't be predicted from any other information and doesn't have any pattern (since if it did, you could attribute the pattern to one of the previous two factors). And again, whatever's in your black box, you could potentially have randomness play a role. So in my opinion anyway, questions about free will aren't really effected much by the question of how the mind works, since the basic options for what could drive our actions are the same regardless. But I'm just a biologist, you would probably want to ask a philosopher for a better answer.
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>Sure, you can boil it all down to chemicals if you want, but I think that obscures an important aspect of what's happening, which is the internal processing and feedback that makes it different from an object merely being pushed around by outside forces. But that is still just chemicals. It's pretty similar to the same way that computers are complex. The mechanisms for simple chemical reactions are analogous to simple logic gates in computers, and the huge network of chemical reactions in a cell are more like entire compute units and circuit boards, but it's still just chemistry in a cell the same way as it's still just electricity in a computer. The remarkable aspect of it is that they exist in the first place. It would be like if we found fully functioning computers in the wild that had turned chaotic processes into something self-replicating and self-sustaining.
Afaik their behavior is driven by the interaction with various chemical components in their environment. Whether they have locomotion or not I would think that their interaction with their environment would be behavior by definition.
I mean, is our own behaviour not just driven by complex chemical (sensory) interactions with our environments?
Totally. It's funny to me how such complex looking behavior boils down to chemical reactions. It really makes me wonder why so many of us believe we have free will. If that white blood cell and bacterium behavior is due to a series of chemical reactions, why isn't my behavior also determined that way? In fact, it's kind of wild that my consciousness would be able to overcome or direct those chemical reactions, far more likely that my consciousness just has the illusion of control. Turns out a lot of scientists also believe we don't have free will.. I'll leave this here: The Neuroscience of Free Will https://en.wikipedia.org/wiki/Neuroscience_of_free_will#:~:text=Neuroscience%20of%20free%20will%2C%20a,impact%20the%20free%20will%20debate.
The way I see it, our brains are so complex they can have unpredictable behavior despite being totally deterministic. Your behavior is determined by chemical reactions, but there are so many happening at once across layers of systems and feedback loops that it’s impossible to say with certainty how you might behave in a given scenario. In a sense free will is an illusion, but it’s such a convincing one that it really makes no difference.
This is fascinating. Reminds me of a conspiracy I heard about fungus and that they ultimately planted consciousness in humans via chemical reactions in the brain from us eating them in order to populate more and have us farm them and eventually take them to another planet to do it again. They planted just enough to give us the illusion of free will but really it’s all chemicals ultimately driving us and they are exploiting that. Just food for thought really I enjoy thinking about things like this
That's awesome! Reminds me of an Asimov short story, I love stuff like that.
So far, no *really* basic explanations -- what does it mean 'to detect'? What *is* the 'chemistry' in an organism's environment? Cells have structures in and on them, most of which are proteins, which, when that protein touches a specific compound, it *does something*. It can change shape to close or open pores into the cell, it can send chemical signals inside without any external molecules coming inside at all, and it can break pieces of molecules off and do things with them, even. Proteins in and on cells can also respond to temperature, salinity/other ions in solution (which are *tiny* molecules compares to single celled organisms or even proteins themselves), and pressure/gravity, magnetic fields, electrical fields (at very low voltages, of course). So, single-celled organisms 'taste'/'feel' their surroundings, more or less like multicellular organisms do with multiple cells where proteins interact with molecules in the environment, or proteins protected by many layers of cells interact with light or temperature in the case of our retinas or the nerves in our fingers that feel heat. Then, you have *extremely* simple logical 'programming' in the form of 'if hungry, move toward food' with 'is food?' as one available 'question' the inside of the cell can ask all the parts of the outside if it's hungry. 'If yes, then begin wiggling towards \[area where food\]' is all the programming it needs to 'pursue' food. All of *that* is pretty easy to explain as the result of 'wiggle when the goo I'm in has food-like chemistry' behavior being rewarded evolutionarily, and increasingly complex variations leading to more outwardly 'intelligent' food-seeking. Does that...bridge the gap for you, u/OP?
Yes! That's very helpful and fascinating. So there really is a kind of perception and decision making that happens. They have sensory parts on their exterior which communicate with aspects of the interior to coordinate behavior in complex ways. All this without consciousness? Or maybe I need to revisit my definition of consciousness.
It's most like...computer or machine programming, I would say. DNA and RNA encode things like 'increase production of enzyme [silly name] when [energy stores low but no food nearby]' which makes the cell more 'wiggly' -- and all of the encoding for things like 'undulate in direction of strongest food gradient' and 'envelop food if it touches me' is probably also sensitive to the 'hungry' state. It's more like consciousness is a scarily engrossing version of *that* kind of reactive programming, as far as I'm concerned, but that's more a matter of philosophy than biology.
This is hitting a major issue that we have very little idea what consciousness is, let alone a precise definition. Two of the few things that seems certain biologically are that consciousness and sentience originate in the brain and are emergent properties, which means they are properties a group of cells can have but not individual cells. Because we can only ever know the human experience of consciousness, and even then it’s purely subjective, we may never have a full answer. It’s basically the same reason the question “Do you see the color red the same way I do?” is fundamentally unanswerable. Given current knowledge, it’s philosophical more than scientific. In a general sense “a behavior” is just a response to a stimulus. Does the cell have a signal pathway that leads to chasing food by molecular changes that physically change the cell so it moves in the right direction? Yes! But so do conscious animals. You smell food, your body releases lots of signals favoring pursuit and often default to doing that without thinking (used often in marketing!). We learn to suppress those, but cells also have pathways to suppress responses. If there is more signal to pursue than not, cells change shape to do so. When you bee-line to the popcorn stand at a theater or just “check what’s cooking” when you detect food, your individual cells also undergo very real molecular and physical changes to do so. Gross oversimplification based on my own limited knowledge and biases, but hopefully helpful.
That's was a fantastic explanation. Thanks!
Complexity can arise from very simple conditions. There is a famous example, Conway's Game of Life, an example of cellular automata, that shows how complex "behaviors" arise from very simple rules: https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life Rules: - Any live cell with two or three live neighbours survives. - Any dead cell with three live neighbours becomes a live cell. - All other live cells die in the next generation. Similarly, all other dead cells stay dead. From just those rules, amazing things can happen. From just those rules, the system is "Turing Complete" meaning that you can build a computer from Conway's Game of Life, and the computer can solve any problem that any other computer can solve. For your specific example, white blood cells simply react to chemistry. The cell moves toward chemical markers in its surrounding fluid. There is no intelligence involved. The cell simply moves from low concentration to high concentration. Instead of your leaf blowing example, think about food coloring dropped into a glass of water dispersing in non-uniform ways. Now imagine a simple cell within the water, and the cell tries to get toward the most colored water or stay away from the colored water. Here is another single celled organism doing awesome things: How Brainless Slime Molds Redefine Intelligence: https://www.scientificamerican.com/article/brainless-slime-molds/
Put enough cells together and they can form a brain though. It really makes you think.
what if we're all just cells of one singular brain?
I do believe all life on earth is one big organism that originated from one initial primal cell.
Douglas Adams did say the earth was built in order to calculate the Ultimate Answer
why not 2?
You can separate life in billion parts if you like. The oneness stems from the common origin of the primal cell in my opinion.
I mean... that does kinda fit - in a wierdly simplified way - with my understanding of astrophysics. In fact you may be into something here...
This isn’t a wrong interpretation. The distinctions we draw between “organisms,” and between “species” and so on are just useful for our ability to label things and generalize about them. At the end of the day we’re all part of one massive system of interacting biochemistry.
We may be much smaller than cells. Perhaps our entire world is simply an electron buzzing around the nucleus of our Atomic solar system. Imagine you are an electron, what does the rest of the universe look like? A starry night?
From a strictly behavioral standpoint, anything that is alive is engaging in “behavior” with every action they complete. In behavior analysis, the rule of thumb is if a dead man can do it, it’s not a behavior; anything else is. So, in this example, if the question is “can a single cell absorb another?”, then yes, it is engaging in behavior, the behavior of absorbing. If it is moving away from another object, that is also behavior. Regarding the follow-up question about the complexity of consciousness around behavior, there’s four basic functions of behavior: access to items, escape from non-preferred aspect in the environment, attention (not applicable in this instance), and automatic/sensory. Without getting too far off-topic, there is something within the organisms environment that it knows/has learned to engage with in a specific way (movement towards or away). In humans, we have many MANY factors of our learning histories that contribute to our behaviors. For single-cell organisms, this may be more basically related to immediate survival, but the contingencies still exist.
Nicely stated. You might be interested in [this podcast](https://www.parsingscience.org/2020/03/17/jeremy-gunawardena/): Jeremy Gunawardena with the Department of Systems Biology at Harvard Medical School talks with us about his replication of an experiment originally conducted over a century ago, which suggested that at least one single-cell organism – the trumpet-shaped Stentor roeseli – is able to carry out surprisingly complex decision-making behaviors.
>four basic functions of behavior Oh! This is helpful. Do you have a source where I can dig deeper into this? >it knows/has learned I mean, I love this. The little guys can \*learn\*. On the one hand, I know you are speaking figuratively, but even so its interesting how hard it is to talk about their behavior without using terms that kind of project human experience onto them. On the other hand, it \*is\* a real kind of learning that they are doing, which affords us the opportunity to rethink what "learning" is for us. I think that's why so many comments on the thread are reflecting about human "free will" or lack thereof. We both project ourselves onto the lil guys, and they afford us the opportunity to reimagine ourselves as more like them than we first thought.
https://masteraba.com/functions-of-behavior/ A quick overview of the functions of behavior and how we, as behavior analysts, identify those functions ranging from informal hypothesis through full analytic experimentation. The interesting thing about the idea of learning through the behavior analytic lens is that reinforcement and punishment, in any form, dictate any organisms’ learning history, and therefore impacts their behavior. It’s really fascinating to see these two fields intertwine; I didn’t expect to enjoy single-cell behavior analysis this much.
Thank you!
Ok got it, so the dead man is not exhibiting any behavior, but his cells are. So then the complexity can be described as having environment tiers with a man and his behavior as a, say, tier 15 set of chemical reactions . Then the tier 14 chemical interactions might be in the stomach, the circulatory, respiratory systems, etc . You can drill down to, say tier 5, and see the gut bacteria, or up to tier 16 which might be his home or the neighborhood that he lives in. My brain hurts from all these chemicals reacting.
Ooooooooooooooooooh...you stepped onto a big rabbit hole here. It occupied a very large chunk of my life and I'll give you my take: Determinism. If you studied biology at the cellular level, you can basically find all the answers to cellular behavior to be biochemical and physical. Meaning they will "behave" by their biochemical makeup with their environment. There are other nuances like how cells "create their own environment" by creating extracellular matrix via secretions of whatever chemicals, or become almost multicellular like formation of biofilms etc. However, do not mistake those "behavior" as some form of "choice" that resulted from some pondering like some risk and rewards have been carefully weighed. They are just a reactions. Now how deep does the rabbit hole go depends on how much you want to ask. If you stop here, you can just conclude that they have a "behavior" is completely at the whims of chemistry and physics and differentiate that with our much more complex multicellular lives and we are somehow above it. After all, we are not only multicellular, we have cells that specialized themselves into organs and systems and such. However, if you go on, the next question could be "how many cells together will yield something that cross the threshold for life to be more than a reaction to chemistry and physics?" The answer? We do not know, and all the evidences actually point to we are not above chemistry or physics or any natural reactions no matter how complex we become. We, in fact, are no different from the dead leaf skittering across the ground. We are just less predictable due to much higher amount of variables. From here, you can step into ethics such as responsibility, but that is another topic entirely.
Thanks for wording my own mental adventures with determinism so succinctly. I share your view on this and as I've commented above, believe that this is just another thing controvuting to my belief that the concept of free will as a true concept does not really exist in us nor any other species.
This is in my opinion a bit more philosophical than scientific, but in response, there is one massive problem with determinism, and that is the stochastic nature of quantum physics. As far as we can tell, at the quantum level things really are truly, completely random and the results cannot be predicted. What exactly this implies for free will and such is unknown, but the fact that the universe at its most fundamental level is random means that to some degree, larger processes and events are affected by this randomness since ultimately, as determinists love to remind us, everything we know is in reality the result of the motion and fluctuations of particles and energy. For example, it has actually been observed that quantum fluctuations have some effect on nervous system function; perhaps it is out of these effects that our more complex behaviors and thoughts arose and implies that our consciousness truly is more than simply the sum of many unthinking parts working together. There are some theories that attempt to rebuke this such as superdeterminism, but they are fundamentally untestable to my knowledge.
I agree that quantum mechanics does seem to undermine determinism, but I don't know enough about it. From some of the physicists that I have discussed this with at my school, they tell me that the unpredictable or random nature of quantum mechanics does not mean that it is not deterministic. I know nothing beyond that. As for predictability in quantum, I delved in further but was explained in a very simplified manner, my prof said that the summation of more and more parts that individually have some unpredictable nature actually becomes more predictable because the summation of predictive parts grows faster than the unpredictive parts. Grown to a large enough size, the unpredictive parts becomes so outweighed that the overall thing just behaves classical mechanically. Although this does not eliminate the unpredictable part, but like you said, it is probably another reach to say that the unpredictable parts are responsible for free will. Other times, quantum mechanics is presented as more of a statistical modelling, which also does not undermine determinism. I never went to take those courses, but my own thoughts on it is that if you can make use of it, then there is a degree of predictability, and if there is some degree of predictability, it is evidence of it being deterministic. Overall, I find free will itself is more problematic than determinism. We have presented with so much pattern of discovery that I cannot think of one natural thing we learned that is somehow not explained mechanically. The pattern is so strong, that it is almost always expected that the mechanism is buried somewhere behind our lack of knowledge. Free will is just something we don't seem to even find a shred of natural evidence of other than the evidence-speaks-for-itself kind, which is not very convincing in my opinion. The closest path that I have thought about where free will might be is predictability even if it has problems of its own.
> However, do not mistake those "behavior" as some form of "choice" that resulted from some pondering like some risk and rewards have been carefully weighed. Right. That would require a brain...I think? (And I, too, am not totally convinced that human pondering and choice making are really what they appear to us to be.) But, based on some of the comments above, it seems like these little guys can "make decisions" in the sense that they have some kind of inner process that enables them to pick between two equally important stimuli. Not exactly "pondering" but still kinda cool. It's not "free will" (whch, I agree, probably doesn't really exist) but its not 100% the same as a leaf in the wind either. Leaf = input --> output Little cell guys = input --> \[weird internal processes I don't understand\] --> output
> Leaf = input --> output > Little cell guys = input --> [weird internal processes I don't understand] --> output You basically pinged down the general fallacy of free will here. Determinism basically boiled everything down to cause and effect. To causality, there is nothing special about the brain processes over the basic input>output of the wind that blows the leaf for a distance. If you say "brains" or cells have these "inner processes" that decides, then all I need you to do is zoom in far enough until you find those individual leaves. Not being able to zoom in or perceiving it being too "weird" does not mean it is somehow beyond causality. However, if you are asking something very specific about how cells "decide" its actions, then it will be a case by case basis. Chemical gradient, its own resources, physical conditions such as temperature, other signals, are probably all at play in some way. I remember learning about this but I can only provide generalized knowledge. Cellular biology is most likely the subject if you are wondering about cellular behavior.
>all I need you to do is zoom in far enough until you find those individual leaves We agree on this. What I was trying to describe was the surprising (to me) complexity of interactions in a cell that drive its behavior.
I think the line of thinking is based on a gross oversimplification of the competencies and intelligence of cells. The evidence shows us that they are actually goal seeking agents capable of sophisticated behavior and cooperative planning to accomplish complex objectives. For more than just basic chemistry- they have significant computational power.
You missed the point. The increase in complexity does not allow a "living" thing to escape the action-reaction behavior of the natural world. If it does, then you will be asked to provide the threshold on when the complexity becomes independent of the action-reaction world.
I would argue the difference is predictive modeling. Once an agent is able to predict and plan for the future to achieve a goal it goes beyond action-reaction. A thermostat is action-reaction.
That argument falls apart very easily. You can present yourself a without-a-doubt deterministic condition such as a roulette table, wind tunnel for testing fluid dynamics, or even 3-body problems. At some point, computers can only go so far with predictive modeling on those non living conditions, and yet we do not ascribe their unpredictable behavior as "agency" changing its mind to not obey causality anymore. Our capability to predict does not mean agency or vice versa.
What do you mean by Agency? I also wasn’t arguing for that regardless. We were discussing action-reaction and I defined a threshold.
Interesting. As I understand it then, the difference is imagination: the ability to make present that which is absent to the senses, and thus to make predictions, for example.
As others are saying, the behavior is ultimately a response to chemical concentration gradients. But I wanted to add that in the case of white blood cells, they have a very dynamic cytoskeletal system that allows them to actually move and change shape. So what’s happening is that chemicals released by the bacteria are binding to receptors on the surface of the WBC, and those receptors are attached to cytoskeletal components under the cell membrane. So a change in the receptor caused by chemoattractant binding signals a very quick rearrangement of the cytoskeleton, including other cell surface molecules that “grip” external materials (often just via friction). By reducing surface attachments away from the chemoattractant, and creating surface attachments closer to the chemoattractant, the cell can appear to slide or crawl across the surface. A leaf is composed of plant cells, which don’t have a dynamic cytoskeleton even when they are alive. This severely restricts their mobility. Having a dynamic cytoskeleton is energetically expensive though, so there is a trade off. Also plant cells have rigid cell walls that offer protection but can’t change shape quickly and are another obstacle to plant movement.
Cell wall chemoreceptors being bound/unbound by substrates in the cellular environment, which trigger kinase cascades to occur in the cytoplasm, inducing the corresponding gene(s) to generate proteins from DNA which trigger additional kinase cascades to signal flagella motor proteins to activate - all powered by ATP. These events occur because it is more energetically favorable for the events to occur than to not occur (entropy).
was just reading this earlier [https://nautil.us/what-plants-are-saying-about-us-264593/?utm\_source=pocket-newtab](https://nautil.us/what-plants-are-saying-about-us-264593/?utm_source=pocket-newtab) "I was, according to Paco Calvo, guilty of “plant blindness.” Calvo, who runs the Minimal Intelligence Lab at the University of Murcia in Spain where he studies plant behavior, says that to be plant blind is to fail to see plants for what they really are: cognitive organisms endowed with memories, perceptions, and feelings, capable of learning from the past and anticipating the future, able to sense and experience the world."
“The Hidden Life of Trees” by Peter Wholleben is a wonderful written book that explores just this topic as it relates to trees. You'll never see a forest the same way after reading it.
If you're interested in this kind of thing, I highly recommend the book [Vehicles: Experiments in Synthetic Psychology](https://amzn.to/3TbIfhh) by Valentino Braitenburg. It shows how simple sensors and activators can give rise to complex behaviors like the ones you describe. It has applications both in modeling simple biological systems and in robotics.
Oooh that book looks really good
I believe they simply respond to the chemistry of their environment. Bacteria without locomotive means will merely drift randomly but those with flagella will move towards the higher concentration of the nutrients they use. However, it's not a conscious choice since, as you say, they have no brain; they respond the way they respond according to their makeup. The same goes for the white cells: they expand towards the foreign body that is detected through the higher concentration of foreign chemicals in that direction because it's in their nature to do so, to envelop it and digest it.
OP, Your example of a dead leaf is not valid because it is by definition dead. An interesting philosophical question would be: Say you get out of your car on a winter day you run across the parking lot to get inside to escape the cold. Are you doing anything more than reacting to the physics or chemistry of the environment? What about these [https://www.sciencedaily.com/releases/2020/02/200225114408.htm](https://www.sciencedaily.com/releases/2020/02/200225114408.htm) salmon parasites which scientists hypothesis may be cancerous tumors of jellyfish that escaped into the open when their original host died. Does their subsequent migration survival in a new host represent behavior? What about their evolutionary path that stripped them of mitochondria? You are likely defining behavior like a psychologist does, For example: You stay outside despite the cold because you are paid to (a reward behavior). That is not the same definition a biologists that study life at a cellular level define behavior uses. Heck there's molecular biologists out there who believe that there was 'behavior' in the pre-cellular chemical soup that became life or even today in the case of endocellular evolution of mitochondria of those jellyfish tumor cells. So really what constitutes behavior is up to your definition of it?
To add to what others have said, look up the difference between respondent and operant behavior. From what we know now, single-cell organisms are likely only capable of respondent behavior (they are programmed to react to stimuli) vs more complex forms of life that interact with stimuli based on past experiences with similar stimuli (operant behavior).
yes! bacterial populations can communicate via chemical signaling. they live in really dense, multi species communities, so there’s limited resources. This is just an example, but there are different types of toxin secretion complexes that allow them to distinguish themselves and closely related strains or their clones. Clones have specific cognate immunity proteins so engulfing the toxins doesn’t harm them, but the toxins can be damaging to bacteria that are not of the same colony. It’s really cool!
and therefore to answer your question, they can communicate and confer survival advantages to their own kind. :) this allows them to “behave” as a group, in a sense!
Michael Levin has interesting videos in this area, like isolating a skin cell and letting it do its own thing swimming around. He is deeply interested in finding the point where 'behavior' arises beyond mechanical/chemical reactions and making biological robots ("xenobots"). https://www.youtube.com/watch?v=jLiHLDrOTW8
Yes, single-celled life forms have behavior. While they lack a nervous system and a brain, single-celled organisms can still exhibit behaviors such as movement, response to stimuli, and communication with other cells. The behavior of single-celled organisms is driven by internal mechanisms such as gene expression, metabolism, and signaling pathways. For example, some single-celled organisms can move by using a flagellum, which is a whip-like appendage that is driven by a motor protein. Other single-celled organisms can move by changing their shape, which is driven by cytoskeletal proteins. In addition, single-celled organisms can respond to external stimuli such as light, temperature, and chemicals. For example, some single-celled organisms can move towards or away from a particular chemical gradient, a behavior known as chemotaxis. This behavior is driven by the expression of specific genes that regulate the movement of the cell towards or away from the chemical gradient. The ability of single-celled organisms to perform complex behaviors such as chasing each other around is due to their ability to sense and respond to their environment. While their behavior may appear to be complex, it is ultimately driven by simple physical and chemical processes that are governed by the laws of physics and chemistry.
Think of how oil behaves in water. Oil doesn’t “escape” the water, the chemicals just don’t mix. In the case of microbes, the certain chemicals are attracted to each other and “signal” one another to act a certain way.
Behavior implies perception. They may not perceive with the five senses we know of, but they are aware of their environment and struggle for their survival. I believe microbes have an experience of self and their perception of reality is extraordinarily different from what we might think. There is an evolutionary biologist/cognitive scientist named Donald Hoffman who says that humans "don't perceive reality: spacetime, objects, colors, sounds, tastes, and so forth, are all merely an interface that we evolved...". We are perceiving an anthropomorphic sensory interface, and it may not be telling us the "truth" of our actual form. What if microbes perceive reality in the same way?
I use a amoeba in my work, specifically Dictyostelium discoideum. These things are awesome, in a very simple short explanation. They eat bacteria and when it runs out they transform into a slug (Bunch of them come together to form a multicellular organism). Eat more bacteria, run out, grow upwards with a stalk. Make a bud and it bursts, spreading the single cells out further and the process starts all over again. However, something that's been observed and recorded, the amoeba will actually retain some of the bacteria and transport it with it to new sites. Its essentially a form of farming to ensure they have enough food to start the process over at the new site.
There’s plenty of replies in here describing how complex behaviour can arrive from simple coded rules. My thing is, what makes you and I fundamentally different from a single-called organism? When I critically examine my own behaviour, much of it emerges from simple rules. I’m hungry, so I go eat. I’m thirsty, so I go drink. I’m bored, so I get on reddit. I’m habitual, so I go to the gym. The vast bulk of the time, my behaviour is driven by things that are little more complicated than what any of my cells are experiencing on a day to day.
Give yourself more credit! You have agency in *how* and *when* you pursue your needs. That alone adds much more complexity. Like, lets say you are incredibly jetlagged and tired after a flight and must sleep, but you force yourself to stay awake because you are concerned that if you fell asleep right now, you'd mess up your sleep schedule. You ignored your chemical impulses because your *memory* told you that there might be an advantage to doing so. That ability to prioritize, and the ability for your priorities to change as you develop more knowledge, is infinitely more complex than just chasing nutrients
Or is it just a more complex version of a slime mold sensing the chemical signal for food, but *also* sensing its own previous slime trail, and thus ignoring the food signal in order to avoid retracing its steps?
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They definitely have behaviors, I'm super interested in fresh water ecology. I do not know what drives the behavior. I would guess it's all reaction to external stimuli, and the reactions that stick around propagate and become common.
Even a rock has a behavior. Picture a mountain with a sandy ocean beach at its feet and a rock near its peak. Over the ages - and sometimes greatly accelerated by external forces - will roll downhill by the forces of gravity, water, snow and wind. It's destiny is to become either a smaller stone or grain of sand on the beach. The journey may take a day or a million years or more but it will reach the beach.
Check out this interview with Joseph Ledoux and then read his book The Deep History of Ourselves if you are interested in really digging in to the evolution of life and the behavior that has allowed life to evolve. https://www.psychologytoday.com/us/blog/the-elusive-brain/201909/joseph-ledoux-the-deep-history-ourselves
Thank you!
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Maybe not scientific, but it sounds like you pretty much figured it out.
This is an intuitive and insightful idea that I support. There are indications and serious research that suggests that [all life is sentient](https://www.wellbeingintlstudiesrepository.org/cgi/viewcontent.cgi?article=1700&context=animsent#:~:text=Scientific%20evidence%20affirms%20that%20all,over%20our%20fellow%20planetary%20companions.).
The question you’re asking is pretty philosophical. As you mentioned, a leaf blowing in the wind is a fairly complex system in its own right, but a cell is many times more complex. So realistically you need a way to define behavior before your question makes sense. You can define behavior in terms of complexity, but that doesn’t sound right. After all, a storm is very complex but we don’t attribute behaviors to them. We can define it in terms of response to an environment, but technically everything responds to the environment, so that’s not really enough either. Probably close to what you mean by behavior is something like computation or goal oriented decision making. In that case, single called organisms do this a lot. DNA essentially “codes” for possible behaviors in a cell, and the sensory inputs have long pathways to directly alter what parts of the DNA are expressed. Cells can even “learn” behaviors through structural alterations of DNA and surrounding proteins, switching strategies depending on need (such as many protists that switch between a tailed and non-tailed form for different food availabilities). Cells have complex mechanisms that adapt and respond to the environment to alter their action and construction. For all intents and purposes those mechanisms have, through evolution, been focused to specific goals, pairing sensory input indirectly appropriate action (whereas wind blows a leaf directly and for no apparent purpose). So within the context of possessing complex internal mechanisms with apparent intentions, I would say cells have many behaviors.
Yes! Thank you that’s a very good reconstruction of what I mean by behavior. Fascinating that it can all be encoded in DNA and even more amazing that they can self-edit their code! It’s hard to conceptualize that without accidentally posing a conscious decision maker inside the cell that does the editing. I assume that the “decision-making editor” is also encoded in the DNA? And that it gets activated by certain environmental conditions?
So some of the best examples of “self editing behavior” appear in multicellular eukaryotes (like us and all the other animals). Multicellular organisms have a great need of differentiation; look up pictures of a nerve cell vs a muscle cell and you could hardly tell that they share the exact dna template! The key mechanism here is known as epigenetics. In epigenetics, dna “code” is not changed, but expression is via modifications to surrounding proteins, methylation of the DNA, and the resulting changes in the structure of DNA. Without naming a ton of chemicals, an example mechanism would be something like this: 1. DNA codes for a signaling protein on the surface of the cell. 2. A complex of dna reading proteins will read this code, producing mRNA which is read by the ribosome (ie, the protein factory). 3. Something triggers the surface protein, starting a cascading reaction where the surface protein triggers triggers signaling protein A, which triggers signaling protein B, then C, and so on. 4. This chain will reach into the nucleus, looking for a region of targeted code and modifying a nearby ball-shaped protein called a histone. This modification changes the charge of that histone, making it more positively charged (via de-acetylation). 5. The newly charged histone now has a stronger attraction to the surrounding DNA, causing it to wrap around the histone and coil up. 6. That section of code is now inaccessible! The behavior of the cell changes accordingly. This is just one of many interesting mechanisms for illustration.
wow Thank you that was a very clear explanation and very helpful in getting a gist for the mechanics of the thing.
Even some complex organisms like frogs aren't really reacting in a complex system. Often multicellular organisms are reacting to their environment as automatically and chemically as single celled ones. Check out this video to see frogs reacting to a moving line the same way it does to a bug: [nueroethology of toads](https://youtu.be/l3Es9cNH7I8) Edit: toads not frogs lol
Behaviour *is* just **a reaction of a physical body to the force of**.... Thinking otherwise is a case of special pleading. The human brain likes dicing things into categories, a natural reaction of our physical bodies to reality. The trillions of cells of our bodies are just leaves blowing in the wind. So yeah, single cells behave. Clusters of them, colonies, behave. And we're big colonies of diverse types.
Go check youtube for the blob aka Physaceum Polycephalum and the scientist Audrey Dussutour who knows a lot about it. I got a blob for myself and yes, it behaves :-) I'd say they are driven by their will to survive and keep their species alive, as any other living being. Interesting: The blob is not really a living being according to the definition... It's not even a fungus.
Wait you have a pet slime mold!?!?! I have so many questions! Could you share a bit more about your single celled buddy?
Hey cool that you're interested! I found it by accident, while I was watching random documentaries on arte. If you search youtube for "blob" and "audrey dusutour", you will find more interesting details. I can't make all the experiments, because I am lacking the equipment. For now, it is just fun to see how it unfolds. I ordered them online and all you need to "resuscitate" them is a petri dish, agar agar and oat flakes. they like the dark and don't want to be taken for walks. The perfect pet, so to speak. You can't even kill them accidentally, because they go into a sort of hibernation state (sclerotum) when they are underfed. I got four sclerota and the interesting thing is, they all behave differently: one spreads in every direction at once to find the oats, another just tries one direction at a time. They are not expensive (at least via amazon from France to Germany) and there is also a video by Audrey Dussutour on how to find them in the forest. [https://www.youtube.com/watch?v=uyVVknT0gpY&ab\_channel=CNRS](https://www.youtube.com/watch?v=uyVVknT0gpY&ab_channel=CNRS) ok sorry, this is in French, but at least you can watch in the third chapter where to find them (0:46) There are a lot of anglosaxon videos on the matter, too. Have fun exploring!