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Imagine a large room, perhaps 50 metres in length and 35 in width, with its ceiling 40 metres above the floor. On this ceiling, there are LED lights, rendering the brightness of the room to look something like this:

A well lit room

On the floor, there's a large pool, stretching 10 metres deep below the floor, and occupying about 60% of the floor area. The remaining 40 percent is covered in a few-inches-thick layer of dust. Now, imagine that the lights on this room would somehow stay turned on for all eternity, and the walls would never break. Some kind of device regulates the gases in the room, so that it stays 78% nitrogen, 21% oxygen, and the remaining 1% of Earth's other current gases.

If we were to deploy a strain of aquatic bacteria into this hypothetical room, and waited billions of years, would it be feasible for things like sexual reproduction, complex multicellularity, and eventually air-breathing fauna to evolve? The major differences here from the real world are:

  • The confined space
  • The lack of change (Same space, same light, same air etc.)

So, do these prohibit the likes of bacteria evolving into as complex organisms as we see on our Earth? Can extremely complex ecosystems exist in a 40 m x 35 m x 50 m space? A further clarification: imagine this room is on Earth, so the gravity will be Earth-like.

Bonus question: could macroscopic flying animals evolve in such a small, windless, thermal-less place? Feel free to ask more questions on the conditions of the room if I've left any out.

EDIT: the founding bacteria will be photoautotrophs, and once they have reached a stable population, heterotrophic ones will be introduced.

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  • $\begingroup$ What are those bacteria supposed to eat? $\endgroup$ – AlexP Oct 13 '18 at 12:26
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    $\begingroup$ You should read A Microcosmic God. Not quite the same premise, but similar (and a damn good read to boot) $\endgroup$ – Joe Bloggs Oct 13 '18 at 12:35
  • $\begingroup$ @AlexP edited to clarify. $\endgroup$ – SealBoi Oct 13 '18 at 12:49
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    $\begingroup$ Mandatory XKCD: xkcd.com/350 $\endgroup$ – John Locke Oct 24 '18 at 16:21
  • $\begingroup$ add a food source and maybe we can talk... $\endgroup$ – SilverCookies Oct 25 '18 at 9:44
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I will begin from the same argument as Roger above:

Cyanobacteria

These bacteria are useful due to (direct quote courtesy of Roger):

  • Carbon fixation. They can pull CO2 out of the endlessly-refreshing atmosphere and convert it to something useful and cumulative.
  • Nitrogen fixation. They can also pull N2 out of the atmosphere and give us ammonia and other useful compounds.
  • Colonies. They can form sheets, which is useful for helping our body of water stay heterogenous, with a well-lit aerobic zone on top and a dark anaerobic zone at the bottom.

This gives us a good starting point. We have a form of life than is generating basic organics, as well as stratifying the environment into useful layers. This will become important later on. If we assume the "dust" is moderately nutrient rich, we also have an initial biomatter to allow normal reproduction (as even asexual reproduction requires some nutrients to be present).

Over time, this will introduce evolutionary pressures. Ammonia concentration in the water will increase over time, as will the presence of complex organics.

Ammonia and Nitrogen Compounds

The increasing concentration of nitrogen-containing compounds will apply an evolutionary pressure as it builds from harmless to caustic levels. This will also have the effect of slowly increasing the volume of the liquid present, while compressing the "atmosphere". We have assumed that the walls will never budge or burst (and are completely non-porous), and that the atmospheric concentrations are kept uniform. This then is a isochoric process. This implies that atmospheric pressure will increase over time. This will increase the levels of dissolved gasses in the liquid, as well as the overall temperature of the system. This is where the system diverges one of two ways in the short term.

If the device also extracts gasses that aren't "normal", gaseous ammonia, water vapour, and other compounds will slowly leave the system. Let us assume that the device operates at some flow rate K litres per minute (STP). If this flow rate exceeds the rate of nitrogen production and evaporation, the atmosphere will stay approximately earth-like indefinitely. We can call this the well-regulated system. Conversely, if the rate of gas generation and evaporation is greater than the flow rate K, then "seasons" will form. This can be the badly-regulated system.

The well-regulated system

In this scenario, temperature, pressure and atmospheric gasses will all remain at roughly starting levels. This scenario is "less interesting" in that it has lower evolutionary pressure. I will discard this scenario as we are specifically trying to force evolution.

The badly-regulated system

In this scenario, gasses are regulated, but poorly, or not quickly enough. This is the more interesting scenario. Temperature, pressure, and concentration of nitrogen compounds (especially ammonia) will increase until it reaches critical levels and begins killing the cyanobacteria. This will purge any members of the population with low ammonia, pressure, or temperature tolerance, leaving only the strongest members. The purge has two useful effects:

  1. Evolutionary pressure. The purge ensures only the "fittest" survive.
  2. Self-regulation. The sudden decrease in bacteria will slow the nitrogen production, and should allow the atmospheric purifier time to re-adjust the atmosphere.

I will designate the less hostile season "summer", and the more hostile season "winter". The system will start in summer, and the first winter will take a long time. Despite this, it will probably be one of the largest purges in this system. Conditions will become violently hostile in multiple ways, and very few bacteria will survive this. It is also entirely possible that the first winter is a 100% extinction event. In this case, the experiment can be restarted. If we have no way of observing the system, the experiment should be run in parallel to maximise the chance of a successful set.

The survivors of the first winter will form the base population for the second "year". These will be the most chemically and physically resistant of the initial population. Thus, population growth will begin again in a more toxic environment than their predecessors. This will specialise the bacteria with each winter, and encourage mutations that enable survival in the hostile environment, as well as rapid population growth once summer rolls around.

Now that we have a system that encourages mutation, we can begin to answer the question.

If we were to deploy a strain of aquatic bacteria into this hypothetical room, and waited billions of years, would it be feasible for things like sexual reproduction, complex multicellularity, and eventually air-breathing fauna to evolve? The major differences here from the real world are:

  • The confined space
  • The lack of change (Same space, same light, same air etc.)

So, do these prohibit the likes of bacteria evolving into as complex organisms as we see on our Earth? Can extremely complex ecosystems exist in a 40 m x 35 m x 50 m space? A further clarification: imagine this room is on Earth, so the gravity will be Earth-like.

Bonus question: could macroscopic flying animals evolve in such a small, windless, thermal-less place? Feel free to ask more questions on the conditions of the room if I've left any out.

EDIT: the founding bacteria will be photoautotrophs, and once they have reached a stable population, heterotrophic ones will be introduced.

Let's break it down.

Multi-cellular life

It is possible for multi-cellular life to form here. The ocean will eventually be home to many nitrogen-based compounds, and the high pressures of winter may encourage complex molecules to form, including amino acids. Decomposing bacteria will also add biomatter to the equation. This will take many "years". However a "year" here is a summer->winter->summer cycle, not a year as we understand it. The main thing that hinders complex life is that as a being's complexity increases, it's energy efficiency decreases. This provides a practical upper bound for complexity (and size) within our mini-ocean. We could see the evolution of macroscopic life (after all, 1cm^3 is still tiny in the scope of the "world" it lives in), however, it will most like either (de-)nitrifying, or photoautotrophic as light and nitrogen will be the most abundant resources to consume.

Macroscopic fliers

The ability to fly (or jump really far) might be developed, however there are few evolutionary pressures to force this. The system will develop thermal currents and winds as during "autumn" and "spring", but there is little food in the air, and little benefit if a lifeform can fly. However, airborne bacteria that can survive on just ambient moisture and nitrogen gas may well form.

Sexual Reproduction

N.B. This is not my specialty, so I will defer on this point if I am incorrect. The system I have posited becomes extremely hostile periodically. While sexual reproduction may form, it would not be particularly desirable from my baseline knowledge of evolutionary selection.

Air-breathing Fauna

This one depends on what you mean by fauna and what you mean by air-breathing. A multi-cellular organism that consumes nitrates, and produces nitrogen gas (like a more complex de-nitrifying bacteria) would be perfectly at home in this environment, and it would be "air-breathing". If you mean oxygen-consuming specifically, then it is possible that a fauna may form that is photosynthetic during summer and nitrogen-breathing during winter (when the "sun" is covered by clouds of nitrates). I'm not aware of any physical or chemical limitations that would prevent this from happening, however, the mutation may simply never occur.

Conclusion

It is entirely possible for you to generate complex life and force evolution in a number of interesting ways in your mini-world. However it does require rigging the process a little bit to maximise evolutionary pressure, while not going so harsh as to kill everything. Additionally, the physical bounds of the world (Watts of sunlight, volume, presence and type of atmosphere, nutrient presence and replacement) have to be carefully calibrated to prevent mass extinctions, or failure to evolve at all.

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    $\begingroup$ If the maintenance system is maintaining the level of carbon dioxide and water in the atmosphere, the room will slowly fill with biomass as CO2 and H2O is pulled from the air and converted to biomass. $\endgroup$ – Jack Aidley Oct 30 '18 at 10:31
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Macro Evolution and Fauna, No.

You might be able to get amoebas and some basic algae but that's it. If this counts as 'macro' to you then your scenario fits the bill. However the reason you won't see anything larger than this comes down to two key constraints of your system, and several honorable mentions.

  1. The rate of energy entering the system is constant, and is too low to accommodate large life forms. The only source of energy in this system are your lights. The total energy emission from your lights is going to be pitifully low compared to the energy requirements of almost any multicellular organism. Also keep in mind that these lights first have to be captured by photosynthetic organisms (with less than 100% efficiency). Then anything that eats said photosynthesizers is going to have to convert the organic matter and get an even smaller percentage of that energy. So the actual energy entering this system is going to be a fraction of the ceiling lights output, which is already very small. Simply put there is just not enough energy to maintain anything but the most sessile, minimalistic organisms (Algae, phytoplankton, but probably something more like Prochlorococcus).

  2. There is not enough space for a population to grow and escape extinction from random chance. You may get sexual reproduction but in such a small space, with limited energy intake, and the strong prevalence of inbreeding anyway, asexual reproduction seems like the clear winner. The limited space will be the driving force for; favoring asexual reproduction, capping your population size, and capping your maximum organism size.

    Population size is limited because as organisms get bigger they require a bigger cut of the energy pie to survive. Since the total energy available is not much the point where an organism's average size becomes too big for a sustainable population will be reached very quickly. This is because they have to divide the available energy amongst themselves.

    Now a population needs at least a certain number of member in it in order to avoid the high risk of going extinct by accident. An example of spontaneous extinction would be every member contracting a lethal mutation, disease, or just dying from stochastic influences. An example of a stochastic event is if every member of a species just happens to not eat today and dies.

    This low population size is going to be one of the barriers preventing organisms from getting too big. This is because if they get bigger they will inevitably go extinct, eventually, even if only by chance. So evolution will favor keeping them small at the point where they are stable. What this size is in your system I don't know, but it will be very small.

Honourable Mentions:

A. There is a fundamental lack organic material. Presumably the only materials available are the air, dust, and bacteria already present. This doesn't give a bacterial population much to work with in order to expand. Sophisticated life might never occur because crucial elementals and substances are missing.

An interesting idea:

If you can find someway for the organisms present to take advantage of the infinite amount of oxygen, nitrogen, etc available in this room (the ratios never change and are always refreshed) you may find a possible energy source for large multicellular organisms, by virtue of energy from chemical reactions.

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    $\begingroup$ For all these reasons mentioned it just isn't going to happen. Your only way to avoid it based on your set up is to some how have an ecosystem based off the air supply. But the biochemistry of this would be so far outside what we are used to it is hard to predict if it is even possible, let alone feasible. The energy to run the system just isn't there without different inputs. Unless you assume no energy loss from the system. In that case the lights would constantly increase the energy until everything was cooked. $\endgroup$ – Crouse Oct 24 '18 at 3:00
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    $\begingroup$ Don't you mean less than 100% efficiency? $\endgroup$ – Renan Oct 24 '18 at 5:29
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Let's start with the most obvious inhibitor - lack of change.

While evolutionary change is fundamentally random at the organism scale, natural selection isn't. Natural Selection is basically the process whereby the 'best' random mutation or change is selected for the given environment. That is important because in an environment where nothing is changing, evolution can expect to occur at a very slow pace, especially after the initial adaptation has taken place.

Why? Because once the organism has adapted well enough to reproduce on a regular basis, nature is going to 'prefer' organisms that maintain the status quo. Admittedly, very occasionally (and at an increasingly lower level of probability for every time it happens) a random mutation will 'improve' surviveability in some way that actually improves reproduction likelihood as well. When that happens, there will be a subtle shift, but could take thousands of generations to propogate through the majority of the population because the existing model is 'good enough'.

What change in the environment introduces is new imperatives to adapt. In other words, once the organism is 'good enough' for the current environment, it has to adapt to the changes in the environment.

When you get right down to it, what this means is that life on the Earth has evolved so much because the environment has been constantly changing.

To put that in context; we currently believe that photosynthesising plant life originally evolved on an Earth with much less oxygen than it has now. There was also no food, after all life was very young, so photosynthesis allowed plants to create their own oxygen and food.

Moving on to nutrients.

In your artificial environment, there's plenty of oxygen, so you might not need photosynthesis to survive. Also, depending on what's in your 'dust', there may actually not be all the nutrients in the environment to support wholesale biomass increases that could occur through a species becoming successful. The nutrient (rather than energy) balance of the room may actually be the limiting factor here. Sure, chemical energy like sugars would be useful, but you are introducing a constant amount of energy and maintaining an environment in which your initial bacterial species can thrive, but if there are not the basic elemental building blocks available for DNA and biological replication, your species still can't grow.

Even in a nutrient rich environment, as has already been said in other answers there is a constant flow of energy into the system and the atmosphere is preserved, so your bacteria may well grow to accommodate the existing nutrient base. Unless that somehow changes the environment however, you may well just run the risk of a flame out; life growing to a point that's unsustainable in the environment causing your own mass extinction. The balance will be interesting to maintain, and in so doing you also remove the chance of environmental change and we're back to the original problem.

Finally, let's look at the issues with atmospheric control.

Maintaining your atmosphere may well end up being the most toxic thing you can do for your organisms. Remember that these are carbon based life forms, meaning that for the most part (this is an over-simplification, but bear with me) you can expect your organisms to breath in oxygen and release carbon-dioxide. But, that carbon is important to the eco-system. You can't just filter it out of the atmosphere and NOT return it to your closed environment. Ultimately, you'd end up with a critical shortage of carbon in your environment, and life would again not have the building blocks it needs to reproduce.

Ultimately, you want the closed system to create its own oxygen. If you don't, then you are not creating any form of equilibrium that balances itself depending on the current needs of the environment. You want plants to thrive from a lack of predators when oxygen wanes, to increase the oxygen. You want animals to eat the plants when the oxygen reaches sufficient levels and you don't want to over-produce.

It's these kinds of equilibria, on a massive and complex scale, that keeps the checks and balances on life that forces it to change and to evolve on Earth. In your artificial environment, you don't actually want to keep things too 'ideal'. In point of fact, that's the most destructive thing you can possibly do. What you want is for life to figure itself out, find the niche elements of shortage that it can exploit to survive and balance against itself.

As for scale, other answers are correct in saying that you're not introducing enough energy or providing enough area for variation to occur, especially around procreation. If all your organisms can reach or come into contact with all the other organisms in the tank during their lives, it means that your DNA homogenises. The moment that happens, not only do you no longer get the variations you need for evolution, but you also lose the ability to adapt to the changes that may occur in that environment in the future. In practice, that means that if (say) your lights go out for a couple of years until maintenance arrives to change the bulbs, your ecosystem is dead because it didn't have the ability to adapt in time.

Summing up, you need a balance of nutrients, sufficient energy being put into the system, sufficient space for different colonies to form, sufficient variation in the environment for those colonies to have different evolutionary needs, and an environmental control that ensures that the environment is never truly ideal (albeit in different ways at different times). If you do all that, you have a far better chance of seeing the evolution you seek in such an environment.

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  • $\begingroup$ intraspecific competition will keep the organisms changing, but good catch on the carbon loss. $\endgroup$ – John Oct 24 '18 at 13:35
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possible but not likely, the major problem is homogeneity and how small it is. There is little variety in standing condition and not much space so you will not have much variety in the life that is there. Sexual reproduction is the easiest that is about competition withing the same species which exist in this scenario.

Multicellularity is also possible although we do not fully understand what initially drove the evolution of multicellularity, but it is possible and maybe even likely, but we just can't say for sure.

The catch is air breathing fauna since there is no reason to evolve it, earth fauna evolved air breathing because they lived in oxygen poor water, like estuaries and swamps, no such environment exists in your scenario. Thuw evolving air breathing is not going to happen.

to be clear you are still going to end up with a variety of life in your pool but none will not be large, likely not even visible, and the small size of the pool will result in very limited diversity if you have a few dozen species across the entire pool I would be surprised.

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Probable.

I'm basing this mostly on the characteristics of our starting lifeforms, the photoautotrophic bacteria.

Of particular interest to me is the humble cyanobacteria. This little dude is capable of three important things right out of the box:

  • Carbon fixation. They can pull CO2 out of the endlessly-refreshing atmosphere and convert it to something useful and cumulative.

  • Nitrogen fixation. They can also pull N2 out of the atmosphere and give us ammonia and other useful compounds.

  • Colonies. They can form sheets, which is useful for helping our body of water stay heterogenous, with a well-lit aerobic zone on top and a dark anaerobic zone at the bottom.

That solves some of our biggest problems immediately -- we're getting a good mix of basic organic compounds, and we're changing the chemistry in our aquatic biome.

Is the rate of energy entering the system too low for large lifeforms? I don't think so -- the largest living lifeform on Earth is a fungus. Our new lifeforms might be slow, but I think they could be big enough.

Is the space too small? I don't think so -- bacteria are, well, pretty small. The smallest multicellular life is pretty small.

And a couple billion years is a really stupendously long time.

Is the space too heterogenous? I don't think so. Even if it starts out that way, life itself is going to differentiate that.

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    $\begingroup$ I really like this answer, but it seems to me like you ended it about half way through. Especially that last point about life differentiating the environment. You touched on that earlier with the "colonies", "sheets", and "zones" in the pool, but I would love to see where it goes from there. How does this translate to the "shore", and from there to the "inland" areas? at what point does the fungus come in to play in terms of differentiating the environment? What about shaded areas under fungus caps or plants? etc.? $\endgroup$ – Dalila Oct 24 '18 at 21:37
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    $\begingroup$ I agree with Dalila. The answer is somewhat unfinished. Your start was great and you argued well reasoned, but you did not explain how this scenario could realistically bring forth fauna and flora, and not just big funghi. Or is your conclusion there could not be fauna and flora? If yes, please state this directly in your answer. $\endgroup$ – ArtificialSoul Oct 29 '18 at 8:43
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Some of the answers have mentioned that evolution will only happen slowly, if at all, because the organisms do not have to adapt to change. Really, that is the biggest inhibitor to life getting anywhere in this scenario.

To create diversity, you can introduce a reason for organisms to evolve. Here are two:

Virus

Add a bacteriophage to the room. The selection pressure will kill off similar organisms.

Viruses evolve over time. Take for instance the flu. Each season, a new strain of the flu unique from every other strain emerges. A bacteriophage is a virus that infects bacteria. The bacteriophage in your room will evolve along with the bacteria. Eventually, a mutation will give one bacteria a cell membrane that the virus can't attach to. Immune to the predation that the other bacteria are undergoing, this bacteria will multiply and spread throughout the population. A random mutation in the virus will then create a strain of bacteriophage that is able to infect those bacteria. So begins an evolutionary arms race, with bacteria and virus constantly evolving to stay one step ahead of the other. Whenever a large amount of one strain of bacteria forms, the bacteriophage will decimate that population because it only needs one mutation that enables it to infect all of the organisms in that strain. Now your bacteria doesn't have a choice of whether or not to evolve. If no one group can stay dominant for long, diversity will be high, and that diversity will ensure that the bacteria will evolve.

As the bacteria evolves and some bacteria become multi-cellular organisms with immune systems, the virus will keep evolving to infect eukaryotic cells and circumvent the immune systems. In this case, I see large blob-like organisms with specialized immune cells evolving first, and when other bacteria evolve to prey on them, then both of these organisms will develop locomotion along with brains and nervous system in increasing complexity.

Radiation

Radiation can create mutations in DNA. If you have some material that emits DNA-altering radiation, such as UV lighting or a some radioactive material, it will cause mutations in the bacteria that are potentially helpful, causing the gene to spread due to natural selection. Radiation will also introduce selective pressure towards radiation-resistant membranes and walls. The best way for bacteria to avoid the radiation, which will kill them, is to develop locomotion to move to an area of the pool with less radiation. Bacteria that remain near the source of radiation will have to evolve methods to prevent death by mutation. The bacteria can evolve to fix damaged DNA, or have an outer shell that blocks radiation. Now, there are at least two different strains of bacteria in the pool, so you have diversity. Keep in mind that radiation does not travel far through water, this XKCD What-If says the amount of radiation is cut in half every 7cm.

Conclusion

Both of these options create a selection pressure that favors diversity. With diversity comes predation, and with predation comes evolution to avoid getting eaten. Predation results in complex life and a food chain. Without selective pressure, your bacteria will settle for good enough and won't evolve.

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