That’s a good question, and I’m pretty sure the answer is that generally, life would evolve in that “order” of germ layers.
The big idea behind germ layers within an evolutionary lens is that organisms first evolved components that arise out of the endoderm and ectoderm because those represent the logical next steps in complexity on the path towards developing complex organs . For example: an organism would need something akin to a gastrointestinal tract to develop a stomach, a large intestine, etc. that comes out of mesodermal tissue, and an organism that becomes macroscopic would likely need some sort of tissue devoted towards skin and the outer layer, as is seen in ectodermal tissue. So I would think that organisms as a whole generally follow the same “outline” of sorts when it comes to having endodermal, ectodermal, and mesodermal tissues arise.
That said, there is some variance among many triploblastic organisms in, for a lack of a better word, the “proportionality” of mesodermal and endodermal tissue for a specific advanced organism. To be more specific and clear, certain organisms might have a stomach that has a lot of function derived from mesodermal tissue, while other organisms have a stomach that is mostly endodermal with just a few mesodermal tissues devoted to them in development. So perhaps this can indicate that the types mesodermal tissues don’t necessarily have develop in the same order - there isn’t, say, a necessity that the lungs evolve before the stomach, that a circulatory system evolves last, stuff like that. I’d like theory input on this topic however.
In light of discussions on Discord, I wanted to post a though regarding how to approach the transition to tweaking body plans instead of individual cells.
I think we should first think of the broadest level of detail first - how editing the entire organ system will work - before we think of the finest level of detail - creating and editing individual cell types that compose specialized tissues. By that, I essentially mean instead of designing an organ system by having the players place down tissues they made to be a neuron or a vessel or a whatever, we’d essentially generate the system automatically, think of the broadest scale first, and find some small-scale areas/details for the player to tinker with.
I can foresee many problems that may occur with the first approach, of making the player design an entire system by placing individual parts:
Can be way too iterative, where you may only have enough MP to place maybe half of a nerve net you’ve been meaning to place, or half of a muscle
Requires sooooooo much work for so little output: would we be designing specific components for tubular blood cells, neurons, skin cells with oils and secretion, fat cells with lipids, digestive cells with special cilia, etc. that would realistically only be useful for a single type of cell?
There’s variations within the cells of a specific tissue as well - short twitch v. long twitch muscles, long neurons vs short neurons, different types of epidermis - that would be unruly to implement
I really just don’t see how we can assume that the player will have enough knowledge and skill to place cell layers in a way that ends up in something like a limb with bones, vessels, nerves, muscle cells, etc.
Whereas I can see a lot of benefits from the latter approach, of providing a broad organ system automatically to the player, prioritizing broad scale changes, and finding small areas to allow things like the editing of cells:
Can reduce tediousness and repetitiveness, as it would be annoying to have a limb that is otherwise perfect except for the fact that you haven’t perfectly synched nerve network, blood vessels, etc. Structures don’t form system by system as they probably would with a limited MP pool; that assumes too much foresight and planning from evolution.
We really need to ensure that we don’t overwhelm the player with designing different cell types for different organ systems at the same time. By providing a broad template for the player to tinker with, we have a steady and controlled way to introduce anatomy to the player.
Let’s us focus less on devoting resources to incredibly small components (specific organelles of cells and tissue types) of what will undoubtedly be a huge stage (macroscopic) and let’s us focus on making sure the game flows as well as possible. It makes it easier to envision a nervous system when we don’t worry first and foremost about the individual neuron for example.
So, what does this mean? The transition should probably involve a pretty large jump in complexity where a player is provided with the most basic forms of advanced organ systems. So instead of approaching the transition to the macroscopic stage by thinking of ways to create different highly specialized cells, like neurons or blood cells, think of ways we can involve cool broad, macroscopic tweaks to those very basic organ systems. Then, from this broadest level of detail, perhaps we can work our way down to figuring out opportunities to involve the player’s control over details as small as individual cell anatomy.
Here’s what I’m doing for the prototype regarding this. As it continues from the early multicellular prototype, all of the cell types the player has created will be carried over and can still be edited and duplicated like before. The editing is done with the microbe editor except there will be a few multicellular exclusive organelles. In late multicellular the placement of individual cells is replaced by placing down metaballs. These metaballs have a size, position, and parent which define the metaball structure. In addition to that each metaball has an associated cell type. So basically the cell types define which type of tissue each placed metaball is. I’ll keep it simple initially and probably have just two specialized cell types (designated by placing the exclusive new organelles): neurons and muscles. Placing enough total volume of neurons will be what unlocks the aware stage, and for muscles I was thinking that the player could select the muscle type when creating a joint between metaballs, which would have some kind of effect on the joint in the future.
That’s basically how I imagine the base body shape will be done even once the late multicellular is no longer a prototype. This model doesn’t address blood vessels or any kind of systems like that. I think we should probably leave designing those parts of the game until the basic metaball based editing is done and we get feedback. We should carefully balance how many systems the player must juggle at once in the late multicellular stage, it should not be overwhelming.
Fleshing Out Hydrostatic Skeletons, Endoskeletons, and Exoskeletons
In an effort to create greater clarity on our plans for the macroscopic stages and seeing as the base of this concept seems to be well-received, I would like to jot out some thoughts I’ve had building on this base concept. Insight and opinion is, of course, very much welcomed.
Looking at metazoans, there are various methods through which organisms “create” structure in their body plan. A large majority of diverse animal groups are soft-bodied creatures, typically relying on a hydrostatic skeleton with no solid objects to root things like muscles on. Vertebrata utilize an endoskeleton, with an internal bone structure as a root for muscles and more advanced organ systems. And there are exoskeletal creatures, such as arthropods, who utilize an exoskeleton to give themselves form. Note that another major structural group are shelled organisms, such as snails and other molluscs, that utilize a hard substance as a structural anchor as well; but those are technically considered to be soft-shelled creatures with unique adaptations.
Those different types of structures come with their own costs and benefits, and define heavy implications on morphology. Organisms with an exoskeleton demonstrate a heavy level of segmentation due to their rigid bodies. Their genome has adapted towards this explicit segmentation, allowing them to replicate limb structure much more easily than a vertebrate genome can - the latter needing to ensure that multiple resource-intensive organ systems coordinate to create a functioning limb. However, organisms with exoskeletons face limitations with their size on land, need to molt, and require special adaptations to ensure a proper exchange of gas and adequate sensory information. Organisms with an endoskeleton, such as vertebrates, are much more resilient against the square-cube law, allowing them to deal much more easily with size.
Exoskeleton (Arthropods)
Pros
Segmentation Means More Replicable Parts - Segmentation is a lot more explicit in arthropods than in other organisms, with each segment being its own defined part of a body (thorax, head, abdomen, etc.). The arthropod genome has structured itself around this segmentation, meaning genetic material for a limb can essentially be “copied” much more easily than it might be for a vertebrate, allowing arthropods the ability to have a large number of limbs and appendages.
Greater Protection From Environment - A tough external coat of armor surrounding the entire body protects from blunt trauma and predation.
Easier to Keep Moisture In - It is much easier to keep moisture within a solid and rigid object than it is for a continuously exchanging medium, such as skin. This effectively means it is easier for arthropods to make the transition from water to land, and vice versa.
Cons
A Lack of Flexibility - Because the entire body is covered by a chitinous coat of armor, arthropod joints tend to have much less dynamic flexibility than a ball-and-socket joint in vertebrates have. This can limit speed and agility.
Molting - A rigid exoskeleton cannot continuously grow alongside an organism, so it must be shed every once in a while. Not only does this leave an organism vulnerable to predation, but it requires intense effort and can potentially take away from efforts to gather food and other resources.
Limited Size And Less Force Potential - Compared to an endoskeleton, an exoskeleton is much more subject to the square-cube law. Not only does this mean that arthropods cannot grow as large as other organisms, but should they theoretically reach that size, they would not be able to exert the same amount of force on their skeleton as a vertebrate might.
Gaseous Exchange Limitations - The same property of a chitinous membrane that allows them to retain moisture better than other organisms also limits gaseous exchange between an arthropod’s internal systems and the environment. This means less efficient respiration, which essentially means limitations to sizing up on land.
Endoskeleton (Vertebrates)
Pros
Happy Mediums - Organisms with an endoskeleton receive the benefits of having a robust skeletal structure, but are not as constrained than organisms with an exoskeleton in terms of movement and flexibility. They are also able to maintain gaseous exchange through skin, meaning a capacity for efficient respiration remains.
Greater Capacity for Size - Internal skeletons are much more capable of accomodating the square cube law than an exoskeleton, meaning a greater capacity for attaining size and preserving strength at said size.
Greater Force and Flexibility Capability - Being less rigid than an exoskeleton, endoskeleton-bearing organisms are able to exert force at a more dynamic joint range. This allows for greater strength, size, and other forms of force projection at size.
Cons
More “Set” Body Plan - Especially at larger sizes, it takes a lot to make an endoskeleton work properly. Because of this, rather than “simple” replications of segments as seen in arthropods, stem cells in a vertebrate embryo have to carefully coordinate expression so that development proceeds as needed. This essentially means that appendages aren’t as easily replicable in vertebrates as they are for exoskeletons.
Vulnerability of Exposed Skin - A greater capacity for gas exchange means a greater need for protection against the elements. This means the initial transition to land is harder for vertebrates than it might be for arthropods.
Hydrostatic Skeletons (Soft-Bodied)
Pros
Much Use, Little Resources - Soft-bodied organisms are able to conduct a great amount of their biological processes through simple membrane gas-exchange. They are also able to maintain structural integrity without need for dense skeletal structures, relying only on the presence of fluid/water. This allows great regenerative capabilities and requires little structural complexity. It also means a great amount of diversity in terms of soft-bodied body plans: jellyfish, octopi, molluscs as a whole, and all sorts of worms utilize soft-bodied skeletons.
Incredible Flexibility - A soft-bodied organism is able to fit through any crevice as long is said crevice is bigger than any potential hard-body structure (octopi beak, shells, etc.). This allows strong tunneling abilities, and allows organisms to hide in very discrete areas.
Lightweight Buoyancy - Lacking a dense skeletal structure, soft-bodied organisms don’t need as many adaptations should they be filling a niche near the ocean surface.
Cons
Limited Force Projection Capabilities - Because they have no anchoring point for muscles to utilize, soft-bodied organisms have limited force protection capabilities. As such, they don’t move very fast, and aren’t very strong.
Heavy Dependence on Water - Organisms with hydrostatic skeletons require a constant fluid source to maintain structure. Furthermore, because they have limited muscle strength, soft-bodied land organisms have very limited movement capabilities.
Very Limited Protection - Unless they have a shell, soft-bodied organisms are very vulnerable to abrasive force.
Limited Structural Complexity - Without skeletal units, fine structures, such as advanced graspers and jaws, are incredibly difficult to evolve. Soft-bodied organisms must rely on more nuanced structures, such as tentacles and suckers.
WHAT DOES THIS MEAN FOR THRIVE
I notice that much of our discussions regarding how the editor will work are centered around organisms with endoskeletons. If we wish to adequately represent metazoan diversity, it is important that, depending on the player’s choices, the way the editor works will work differently depending on the morphological choices the player has made. While this means more work, I do think the underlying plan - metaballs and convolution surfaces - can work across all three forms of metazoan structure.
What I think will have to happen is essentially having different tools be available to players in the editor depending on the morphological choices they have made up to that point. This doesn’t necessarily mean that we will need a variety of parts - instead, the basal parts we offer to a player will have to behave slightly differently depending on if a player has an endoskeleton, an exoskeleton, or a hydrostatic skeleton.
I won’t go into too much detail with limbs since I feel like that’s a bit of a different topic, and so that the ideas contained within this thread can be reviewed first by you guys. For now, I’ll cover potential general differences and how editing the torso will work.
I also attached some boot-leg concept arts for some ideas I want to make sure are made a bit more clear than they might be just in text. Once again, apologies for their relative lack of quality, but I think they illustrate whatever point I am trying to emphasize.
Hydrostatic Skeletons (Diploblastic or Triploblastic)
Editing the Torso - Soft-bodied organism metaballs will probably operate a lot like vertebrate metaballs, but will have a lot more freedom in terms of playing with the properties of each metaball. To clarify more, remember how in Spore, increasing the size of a certain metaball along the spine would also make other metaballs increase in size a bit? For soft-bodied organisms, that effect will be a bit less emphasized so that one metaball will have less of an effect on another. This will allow more creativity with shapes.
Editing Limbs - One unique thing with soft-bodied organisms I think would be cool to see reflected in game, while also giving them a unique trait for the player to play around with, is for the ability for the anterior side of the creature to not necessarily be where its mouth is. I’m thinking of jellyfish and octopi in particular. Perhaps we can attach an ability for soft-bodied limbs to move backwards rather than forwards?
Regardless, the initial investment for limbs for soft-bodied organisms should be rather inexpensive, but modifications for these limbs should be somewhat expensive.
Here are some concepts for various fake organisms, inspired by real-life Earth analogues. Note that for organisms like jellyfish, we would probably need to incorporate a special modification of some sort to create their “caved-in” appearance.
Editing the Torso - Each metaball within the torso represents a segment. To make a certain segment larger than another, the player can highlight specific metaballs and designate them as a group, which will serve an aesthetic purpose (what functional purpose should we attach?). For example, a player who wants to make a millipede like organism wouldn’t want to group any metaball together, while a player who wants to make an insect-like organism would want to group metaballs into 3 groups representing the thorax, head, and abdomen.
The segment with the mouth opening within it will be considered the head segment, and the segment with the anus opening within it would be considered the posterior.
Editing Limbs - Limbs should be rather easy to add for organisms with an exoskeleton, with both the initial investment for the joint and the modification of joints being rather inexpensive.
Concepts to illustrate segmentation. Note that different color metaballs belong to different segment groups. So for the centipede, each metaball is its own segment, for the ant, metaballs are split into three segment groups, etc.
Endoskeletons (Only Triploblastic Organisms)
Editing the Torso - This will probably be rather similar to Spore’s editor, so as of now I don’t think it needs too much explanation. Each metaball within the torso represents a vertebrae along the organism’s spine. You can manipulate each vertebrae to define your organism’s shape.
Editing Limbs - Limbs will be the costliest for organisms with endoskeletons (limb parts will cost more MP for endoskeleton organisms). I think we should make the player specify where they would like to place a joint alongside the spinal cord instead of just having limbs be free dragging akin to Spore, although I am not too adamant about this of course. Once the player specifies this, a single jointed appendage can be placed. From there, players can add additional limb segments.
FINAL NOTES
Apologies if this concept appears a bit messy; I intended to present a rough outline of how we can address the morphological diversity of all metazoans as easily as possible. So I want to see if the basic ideas are sound before potentially spending more effort on the finer details of these concepts. I would like input on if you guys think this system can cover a wide diversity of body plans while presenting a fun way for players to interact with the decision they have made in their organism’s evolution up to that point in their playthrough.
And I would also like some input on whether or not this approach is possible in the first place. I do realize this could be a lot of work to implement, but I do feel like it’s the best way to represent a diverse amount of biota through the same underlying editor system. Much of our discussions have focused on the idea of vertebrate evolution, but I feel it would be inadequate to only provide an endoskeleton and call it an all-expansive simulation of evolution. Regardless, I’m sure we can simplify this further.
We would first need the soft-bodied tools to atleast work properly at the beginning of the macroscopic stage. So if we want to focus more heavily on this aspect in the future, that should be the first stop.
Really interesting work with all the science you’ve pulled up on this thread.
I totally agree with everything in regards to the tradeoffs of soft-bodied, endoskeletal, and exoskeletal structures. Those all seem to be the exact same tradeoffs I’ve seen when reading about the different body types. In fact I will need to bookmark this page for future reference once we get to implementing this. The point about segmentation is also very true, and as you say we need to find a way to make it easier for exoskeletal creatures to segment more easily than endoskeletal ones.
In terms of germ layers, I’ve thought about using them as a way to categorize the Organism Editor before. What I ultimately struggle to see is how such a system will meaningfully contribute to the gameplay for the amount of complexity it adds. What’s more, from what I understand it is mostly a categorization of how different animal organs have evolved (and how they develop as embryos) and does not directly apply to the evolution of plants or fungi. For example there’s no reason to believe life on other planets will also have three layers and evolve the same tissues and organs from the same layers. As such I keep coming to the same conclusion that it just doesn’t seem to be universal enough and game-effecting enough to design the Organism Editor around that (especially since it would add a lot of complexity for the player’s experience in the OE). But I’m curious as to what you guys think.
Since I’ve been away for a while I apologize if there have been newer discussions on this, but the latest concept for early macroscopic (aka the 3D transition) I remember is that once the player transitions to 3D, we assume that they are still so small and basic that they will not have any differentiated tissues yet, and that the specialized cell types they placed in multicellular don’t count as separate tissues. As such, they will spawn in their first 3D generation as a tiny 1cm wide blob of membrane. The blob will resemble the shape that their colony was. They will be only comprised of a single, all purpose tissue called “Mesoglea” or “Mesenchyme” or “Mesohyl”. This initial 1cm blob of Mesoglea represents the entire colony that the player was just editing the generation before. The way that the Microbe and Multicellular decisions translate over is that the starting stats of your Mesoglea tissue are defined by your design as a colony. So for example a colony with many aerobically respiring cells will have an initial Mesoglea tissue that performs a lot of aerobic respiration. If the colony had a lot of contractile fibers, then the Mesoglea tissue will have a higher “Strength” stat than otherwise. If the colony had a lot of adipose vacuoles, the initial Mesoglea will be very energy rich to any predator who feeds on this creature, etc.
Differentation then occurs once 3D has already started. The player can evolve this Mesoglea tissue to have different stats, they can evolve new tissues out of the Mesoglea, they can evolve entire organs, they can evolve to become longer or wider or both, etc.
Not married to this idea or anything, this was just the latest concept that I can remember of what the early 3D stage would look like that seems to cover a lot of the questions that need answering.
Regarding germ layers; I actually find myself coming to a different conclusion regarding their universality, as even complex plants have 3 “layers” of cells (dermal, ground, vascular). I put layers in quotations because unlike animals, plant embryos don’t fold in on themselves, and these differentiated layers continue to develop heavily throughout the plants entire life cycle rather than primarily as an embryo Chapter 12A. Plant Development
A brief google search tells me than fungus development doesn’t feature the same level of cell differentiation, but for complex multicellular organisms, I would assume atleast some analogue to germ layers is needed to meaningfully differentiate cells.
As to their implementation in Thrive, I would think their only purpose would essentially be a way to pace out progression. I think they would essentially just serve to make sure we don’t see an incredibly rapid jump in complexity from simple jelly blobs floating in the ocean to an organism with a fully developed skeleton in just 3 generations. So I would think they would just be a sciencey way for us to justify slowing down game’s pace a bit when a player gets to macroscopic.
Atleast from my memory, there hasn’t been much discussion about the transition to macroscopic gameplay since that initial idea of a mesoglea glob. It seems the biggest difference between that and what I detailed was that for this newer concept, the digestive tract would be formed as you made that jump. I certainly would like a very seamless jump, but I worry about how much we would be asking of the player to form their digestive tract from piecing cells together. Of course however, we could make it as simple as a sort of upgrade however, and that’s what can introduce cell differentiation. It definitely is something to consider.
Regarding the current implementation (as of 0.5.9) the late multicellular editor picks off from where the player left off from the early multicellular. Which means that all of their cell types the player made before are converted into tissue types and all of the placed cells are converted to one metaball each (at least for now, also the conversion is not super good yet).
