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> with eukarya containing all multicellular organisms within the four kingdoms of fungi, animals, plants and protists. This bugs me so much. The four-kingdom s

> with eukarya containing all multicellular organisms within the four kingdoms of fungi, animals, plants and protists. This bugs me so much. The four-kingdom system should have died out decades ago, it's absurdly wrong. For one thing, fungi and animals should be together (opisthokonts) if you're dividing eukaryotes into the major groups. If you consider genetics, there's no such thing as "protists", they're just a whole bunch of small things that were grouped together because we didn't know otherwise. It's more like, Archaeplastida, Excavata, SAR supergroup, Amoebozoa, and Opisthokonta at the moment. The exact list is up for debate, and currently undergoing change. There's plenty of weird things like Hemimastigophora and we're not really sure where they fit yet.

mmooss 2y ago
> The exact list is up for debate, and currently undergoing change. My strong impression is that even the roots of the tree are debated, with competing models that often change. > The four-kingdom system should have died out decades ago First, hopefully not! :) Second, I think it's used because it's the last stable model. Third, it's a model that the public can understand - theres no point in even trying to use "Archaeplastida, Excavata, SAR supergroup, Amoebozoa, and Opisthokonta" unless you are an expert in phylogenics or evolution. Who can understand and remember that?
- calibas 2y ago
  Children can memorize all 50 US state capitals, they can memorize a handful of scientific names. If we really wanted to, we could teach them a much more accurate view of the tree of life. Also, I don't think the four-kingdom system has been taught in schools for a while? I went to high school in the late 90s and it wasn't taught then. It's strange to see people promoting it online in 2025. If adults want to remain ignorant, so be it, but at least teach children the truth. Let them know that life is incredibly complicated, it's a mystery we're still solving, and they could be the ones to help figure it out. Don't overly simplify things for small minds, it creates a false picture and it kills the imagination.
  - neom 2y ago
    May as well add this to the above: https://en.wikipedia.org/wiki/Songline https://en.wikipedia.org/wiki/Songline (large amounts of knowledge can be transferred just fine)
  - bbor 2y ago
    I'm a huge cladistics fan, but insisting that "animal" isn't a useful term is pretty out there, IMHO. Certainly we can (and do!) teach cladistics in high school biology, but does your ideal world have baby books titled with one of the mentioned names...? More personally speaking: what am I missing out by using the four kingdoms? Like, how could that possibly ever backfire in a way that slightly impacts my life negatively, or impedes the scientists studying genetic lineages? There's basically infinite science to "remain ignorant" of, I don't see any justification for an elitist attitude on this nuance in particular.
    - sashank_1509 2y ago
      Why not go the other way, what are you missing if you don’t learnt four kingdoms. Why should that be taught at all. One obvious reason it should not be taught, if it is wrong then it kills curiosity and imagination by giving us a neat story we think is true. In a way it has the same negative effect religion can have but to a smaller degree. Why does the earth exist, because god made it kills all spirit of enquiry. This is the same problem I have with the big bang. This is another theory that kills inquiry. Similar example:
      - 9dev 2y ago
        Well in very practical terms, it gives you a way to name things you see in the forest, to figure out what is edible, and to understand what has a sentience of its own, similar to yours. I don’t mean to be snarky, but it seems like you’re very removed from the reality of normal people and parents out there.
        johnisgood 2y ago
        There is much more to figure out what is edible and what is not. Considering shrooms alone, it is much more "complicated", so much that there are specialists for that, even, but I agree, could be an useful skill, but not for people who do not even leave the city, I think. However, they should know the basics such as "not eating potatoes (or its parts) that are green", and so forth, since that is something you run into even if you never leave the city. Food spoilage in general would be useful to teach, but that is the job of the parents, I would say. That said, my teachers in elementary school always used to tell me that they are our second parents. I can see where they were coming from.
- mjan22640 2y ago
  > Who can understand and remember that? Anybody who is interested in it
- f1shy 2y ago
  At which point started to be important in science that “public can understand”? I think if something is a better explanation for the reality, we ahould go for it, even if it is difficult for the public. Disclaimer: in this case I have absolutely no idea what is better. But the rationale seems wrong.
  - mmooss 2y ago
    We can and, IMHO, should do both. Scientists explaining physical realities, such as gravity, don't use advanced mathematics - it would be pointless.
- idiotsecant 2y ago
  Yes I agree. 4 humors were enough for medieval europe, they're good enough for me!! Who can remember all this complicated 'germ theory of disease' liberal junk?! There must be hundreds of these supposed 'germs' out there! No sir, no thank you!
dreamcompiler 2y ago
And then there are viruses, which don't show up on the tree of life at all because there's no consensus that they even constitute "life."
- Ultimatt 2y ago
  Pretty sure anyone who knows anything about viruses would say they are alive. Or at least as alive as parasitic nano archaea with genomes smaller than the viruses living right next to them... The philosophical way to look at it is humans aren't alive in the space between planets they live inside these little hard shells, then when they get to a planet they go wild using all the other resources around them made of biomass. Viruses are just this, their biome isn't the wider one you participate in instead they are sub-cellular life, in the same way you are sub-planetary life. Humans don't make the oxygen atmosphere on the planet themselves, they parasitize this feature of planets from other life. In the same way viruses use cellular machinery.
  - beeflet 2y ago
    If humans create oxygen with a machine, is that parasitic?
  - ndsipa_pomu 2y ago
    > Pretty sure anyone who knows anything about viruses would say they are alive Whilst I don't doubt that, viruses don't abide by typical definitions of life that would include self-replication. Obviously, they do replicate, but not by themselves.
    - btilly 2y ago
      Men like me also don't replicate by ourselves. Does that mean that we are not alive?
      - ndsipa_pomu 2y ago
        Humans though, can create more humans, but viruses can't create more viruses without using the machinery within a cell that it compromises.
renewiltord 2y ago
One of the great wonders of clustering algorithms is that no matter what k > n you choose, you can construct k clusters. Then we can argue about the clusters and about k. It is said that when Humanity discovers the One True K, the taxonomy will disappear and be replaced by a different one.
boxed 2y ago
From what I've gathered it's been pretty clear for a while now that archea is basal to eucarya, meaning humans are archea.
adrian_b 2y ago
When classifying living beings, a single classification criterion is not good enough. One classification criterion is descendance from a common ancestor, i.e. cladistic classification. In many cases this is the most useful classification criterion, because the living beings grouped in a class defined by having a common ancestor share a lot of characteristics inherited from their common ancestor, so when using a name that is applied to that class of living beings, the name provides a lot of information about any member. However there are at least 2 reasons which complicate such a cladistic classification. One is that the graph of the evolution of living beings is not strictly a tree, because there are hybridization events that merge branches. Sometimes the branches that are merged are closely related, e.g. between different species of felids, so they do not change the overall aspect of the tree. However there are also merges between extremely distant branches, like the symbiosis event between some blue-green alga (Cyanobacteria) and some unicellular eukaryote, which has created the ancestors of all eukaryotes that are oxygenic phototrophs, including the green plants. Moreover, there have been additional symbiosis events that have merged additional eukaryote branches and which have created the ancestors of other eukaryote phototrophs, e.g. the ancestor of brown algae. After any such hybridization event, there is the question how you should classify the descendants of the hybrid ancestor, as belonging to one branch or to the other branch that have been merged. For some purposes it is more useful to classify all eukaryote phototrophs based on the branch that has provided the main nucleus of the hybrid cell, and this is the most frequently used classification. For other purposes it is more useful to group together all the living beings that are oxygenic phototrophs, including various kinds of eukaryotes and also the blue-green algae, and divide them based on the evolution tree of their light-capturing organelles, i.e. the chloroplasts. This is also a valid cladistic classification, because all oxygenic phototrophs, both eukaryotes and prokaryotes, are the descendants of a single common ancestor, some ancient phototrophic bacteria that has switched from oxidizing manganese using light energy, to oxidizing water, which releases free dioxygen. Even when there are no branch merges due to hybridization, there remains the problem that in the set of descendants from a single ancestor there are some that are conservative, so they still resemble a lot with their ancestor, and some that are progressive, which may have changed a lot, so they no longer resemble with their ancestor. In this case, using the name of the entire group provides very little information, because most characteristics that were valid for the ancestor may be completely inapplicable to the subgroups that have become different. In such a case, defining and using a name for the paraphiletic set of subgroups that remains after excluding the subgroups that have evolved divergently may be more useful in practice than using only names based on a cladistic classification. For instance the use of the word "fish" with its traditional paraphiletic meaning, i.e. "vertebrate that is not a tetrapod", is very useful and including tetrapods in "fishes" is stupid, because that would make "fish" and "vertebrate" synonymous and it would require the frequent use of the expression "fishes that are not tetrapods", whenever something is said that is correct only for vertebrates that are not tetrapods, or of the expression "bony fishes that are not tetrapods", for things valid for bony fishes, but not for tetrapods. While in many contexts it is very useful to know that both fungi and animals are opisthokonts, and there are a few facts that apply to all opisthokonts, regardless whether they are fungi, animals or other opisthokonts more closely related to fungi or more closely related to animals, the number of cases when it is much more important to distinguish fungi from animals is much greater than the number of cases when their common ancestry is relevant. Animals are multicellular eukaryotes that have retained the primitive lifestyle of the eukaryotes, i.e. feeding by ingesting other living beings, which is made possible by cell motility. Fungi are multicellular eukaryotes that have abandoned the primitive lifestyle of the eukaryotes, and which have reverted to a lifestyle similar to that of heterotrophic bacteria, just with a different topology of the interface between cells and environment (i.e. with a branched multicellular mycelium instead of multiple small separate cells). This change in lifestyle has been caused by the transition to a terrestrial life, which has been accomplished with a thick cell wall (of chitin) for avoiding dehydration, which has suppressed cell motility, making impossible the ingestion of other living beings, the same as for bacteria. Moreover the transition to a bacterial lifestyle has also been enabled by several lateral gene transfers from some bacteria, which have provided some additional metabolic pathways that enable fungi to survive when feeding with simpler substances than required by most eukaryotes, including animals. So even from a cladistic point of view, fungi have some additional bacterial ancestors for their DNA, besides the common opisthokont ancestor that they share with the animals. Animals are unique among eukaryotes, because all other multicellular eukaryotes have abandoned the primitive lifestyle of eukaryotes, by taking the lifestyles of either heterotrophic or phototrophic bacteria. However for both other kinds of lifestyle changes there are multiple examples, i.e. besides true fungi that are opisthokonts there are several other groups of fungous eukaryotes that are not opisthokonts, the best known being the Oomycetes. There are also bacteria with fungal lifestyle and topology, e.g. actinomycetes a.k.a. Actinobacteria. If we will ever explore other planets with life, those living beings will not have a common ancestor with the living beings from our planet, but nevertheless it will still be possible to classify them based on their lifestyle in about a half of dozen groups that would be analogous to animals (multicellular living beings that feed by ingestion, so they must be mobile or they must have at least some mobile parts), fungi (multicellular beings that grow into their food, absorbing it after external digestion), oxygenic phototrophs, anoxygenic phototrophs, chemoautotrophs, unicellular equivalents of animals and fungi, like protozoa and heterotrophic bacteria, viruses. These differences in lifestyles are more important in most contexts than the descendance from a common ancestor. So while it is useful to have the name Opisthokonta for the contexts where fungi and animals and their close relatives must be included, it is much more frequent to need to speak separately about fungi and other fungous organisms on one hand, and animals on the other hand. I agree that the term "kingdom" is obsolete when used in the context of a cladistic classification of the living beings. Perhaps it should be retained for a non-cladistic classification of the living beings, based on the few fundamental lifestyles that are possible, and which would remain valid even for extraterrestrial living beings.
deleted 2y ago
[deleted]

mmooss 2y ago

> The exact list is up for debate, and currently undergoing change. My strong impression is that even the roots of the tree are debated, with competing models that often change. > The four-kingdom system should have died out decades ago First, hopefully not! :) Second, I think it's used because it's the last stable model. Third, it's a model that the public can understand - theres no point in even trying to use "Archaeplastida, Excavata, SAR supergroup, Amoebozoa, and Opisthokonta" unless you are an expert in phylogenics or evolution. Who can understand and remember that?

calibas 2y ago
Children can memorize all 50 US state capitals, they can memorize a handful of scientific names. If we really wanted to, we could teach them a much more accurate view of the tree of life. Also, I don't think the four-kingdom system has been taught in schools for a while? I went to high school in the late 90s and it wasn't taught then. It's strange to see people promoting it online in 2025. If adults want to remain ignorant, so be it, but at least teach children the truth. Let them know that life is incredibly complicated, it's a mystery we're still solving, and they could be the ones to help figure it out. Don't overly simplify things for small minds, it creates a false picture and it kills the imagination.
- neom 2y ago
  May as well add this to the above: https://en.wikipedia.org/wiki/Songline https://en.wikipedia.org/wiki/Songline (large amounts of knowledge can be transferred just fine)
- bbor 2y ago
  I'm a huge cladistics fan, but insisting that "animal" isn't a useful term is pretty out there, IMHO. Certainly we can (and do!) teach cladistics in high school biology, but does your ideal world have baby books titled with one of the mentioned names...? More personally speaking: what am I missing out by using the four kingdoms? Like, how could that possibly ever backfire in a way that slightly impacts my life negatively, or impedes the scientists studying genetic lineages? There's basically infinite science to "remain ignorant" of, I don't see any justification for an elitist attitude on this nuance in particular.
  - sashank_1509 2y ago
    Why not go the other way, what are you missing if you don’t learnt four kingdoms. Why should that be taught at all. One obvious reason it should not be taught, if it is wrong then it kills curiosity and imagination by giving us a neat story we think is true. In a way it has the same negative effect religion can have but to a smaller degree. Why does the earth exist, because god made it kills all spirit of enquiry. This is the same problem I have with the big bang. This is another theory that kills inquiry. Similar example:
    - 9dev 2y ago
      Well in very practical terms, it gives you a way to name things you see in the forest, to figure out what is edible, and to understand what has a sentience of its own, similar to yours. I don’t mean to be snarky, but it seems like you’re very removed from the reality of normal people and parents out there.
      - johnisgood 2y ago
        There is much more to figure out what is edible and what is not. Considering shrooms alone, it is much more "complicated", so much that there are specialists for that, even, but I agree, could be an useful skill, but not for people who do not even leave the city, I think. However, they should know the basics such as "not eating potatoes (or its parts) that are green", and so forth, since that is something you run into even if you never leave the city. Food spoilage in general would be useful to teach, but that is the job of the parents, I would say. That said, my teachers in elementary school always used to tell me that they are our second parents. I can see where they were coming from.
mjan22640 2y ago
> Who can understand and remember that? Anybody who is interested in it
f1shy 2y ago
At which point started to be important in science that “public can understand”? I think if something is a better explanation for the reality, we ahould go for it, even if it is difficult for the public. Disclaimer: in this case I have absolutely no idea what is better. But the rationale seems wrong.
- mmooss 2y ago
  We can and, IMHO, should do both. Scientists explaining physical realities, such as gravity, don't use advanced mathematics - it would be pointless.
idiotsecant 2y ago
Yes I agree. 4 humors were enough for medieval europe, they're good enough for me!! Who can remember all this complicated 'germ theory of disease' liberal junk?! There must be hundreds of these supposed 'germs' out there! No sir, no thank you!

dreamcompiler 2y ago

And then there are viruses, which don't show up on the tree of life at all because there's no consensus that they even constitute "life."

Ultimatt 2y ago
Pretty sure anyone who knows anything about viruses would say they are alive. Or at least as alive as parasitic nano archaea with genomes smaller than the viruses living right next to them... The philosophical way to look at it is humans aren't alive in the space between planets they live inside these little hard shells, then when they get to a planet they go wild using all the other resources around them made of biomass. Viruses are just this, their biome isn't the wider one you participate in instead they are sub-cellular life, in the same way you are sub-planetary life. Humans don't make the oxygen atmosphere on the planet themselves, they parasitize this feature of planets from other life. In the same way viruses use cellular machinery.
- beeflet 2y ago
  If humans create oxygen with a machine, is that parasitic?
- ndsipa_pomu 2y ago
  > Pretty sure anyone who knows anything about viruses would say they are alive Whilst I don't doubt that, viruses don't abide by typical definitions of life that would include self-replication. Obviously, they do replicate, but not by themselves.
  - btilly 2y ago
    Men like me also don't replicate by ourselves. Does that mean that we are not alive?
    - ndsipa_pomu 2y ago
      Humans though, can create more humans, but viruses can't create more viruses without using the machinery within a cell that it compromises.

renewiltord 2y ago

One of the great wonders of clustering algorithms is that no matter what k > n you choose, you can construct k clusters. Then we can argue about the clusters and about k. It is said that when Humanity discovers the One True K, the taxonomy will disappear and be replaced by a different one.

boxed 2y ago

From what I've gathered it's been pretty clear for a while now that archea is basal to eucarya, meaning humans are archea.

adrian_b 2y ago

When classifying living beings, a single classification criterion is not good enough. One classification criterion is descendance from a common ancestor, i.e. cladistic classification. In many cases this is the most useful classification criterion, because the living beings grouped in a class defined by having a common ancestor share a lot of characteristics inherited from their common ancestor, so when using a name that is applied to that class of living beings, the name provides a lot of information about any member. However there are at least 2 reasons which complicate such a cladistic classification. One is that the graph of the evolution of living beings is not strictly a tree, because there are hybridization events that merge branches. Sometimes the branches that are merged are closely related, e.g. between different species of felids, so they do not change the overall aspect of the tree. However there are also merges between extremely distant branches, like the symbiosis event between some blue-green alga (Cyanobacteria) and some unicellular eukaryote, which has created the ancestors of all eukaryotes that are oxygenic phototrophs, including the green plants. Moreover, there have been additional symbiosis events that have merged additional eukaryote branches and which have created the ancestors of other eukaryote phototrophs, e.g. the ancestor of brown algae. After any such hybridization event, there is the question how you should classify the descendants of the hybrid ancestor, as belonging to one branch or to the other branch that have been merged. For some purposes it is more useful to classify all eukaryote phototrophs based on the branch that has provided the main nucleus of the hybrid cell, and this is the most frequently used classification. For other purposes it is more useful to group together all the living beings that are oxygenic phototrophs, including various kinds of eukaryotes and also the blue-green algae, and divide them based on the evolution tree of their light-capturing organelles, i.e. the chloroplasts. This is also a valid cladistic classification, because all oxygenic phototrophs, both eukaryotes and prokaryotes, are the descendants of a single common ancestor, some ancient phototrophic bacteria that has switched from oxidizing manganese using light energy, to oxidizing water, which releases free dioxygen. Even when there are no branch merges due to hybridization, there remains the problem that in the set of descendants from a single ancestor there are some that are conservative, so they still resemble a lot with their ancestor, and some that are progressive, which may have changed a lot, so they no longer resemble with their ancestor. In this case, using the name of the entire group provides very little information, because most characteristics that were valid for the ancestor may be completely inapplicable to the subgroups that have become different. In such a case, defining and using a name for the paraphiletic set of subgroups that remains after excluding the subgroups that have evolved divergently may be more useful in practice than using only names based on a cladistic classification. For instance the use of the word "fish" with its traditional paraphiletic meaning, i.e. "vertebrate that is not a tetrapod", is very useful and including tetrapods in "fishes" is stupid, because that would make "fish" and "vertebrate" synonymous and it would require the frequent use of the expression "fishes that are not tetrapods", whenever something is said that is correct only for vertebrates that are not tetrapods, or of the expression "bony fishes that are not tetrapods", for things valid for bony fishes, but not for tetrapods. While in many contexts it is very useful to know that both fungi and animals are opisthokonts, and there are a few facts that apply to all opisthokonts, regardless whether they are fungi, animals or other opisthokonts more closely related to fungi or more closely related to animals, the number of cases when it is much more important to distinguish fungi from animals is much greater than the number of cases when their common ancestry is relevant. Animals are multicellular eukaryotes that have retained the primitive lifestyle of the eukaryotes, i.e. feeding by ingesting other living beings, which is made possible by cell motility. Fungi are multicellular eukaryotes that have abandoned the primitive lifestyle of the eukaryotes, and which have reverted to a lifestyle similar to that of heterotrophic bacteria, just with a different topology of the interface between cells and environment (i.e. with a branched multicellular mycelium instead of multiple small separate cells). This change in lifestyle has been caused by the transition to a terrestrial life, which has been accomplished with a thick cell wall (of chitin) for avoiding dehydration, which has suppressed cell motility, making impossible the ingestion of other living beings, the same as for bacteria. Moreover the transition to a bacterial lifestyle has also been enabled by several lateral gene transfers from some bacteria, which have provided some additional metabolic pathways that enable fungi to survive when feeding with simpler substances than required by most eukaryotes, including animals. So even from a cladistic point of view, fungi have some additional bacterial ancestors for their DNA, besides the common opisthokont ancestor that they share with the animals. Animals are unique among eukaryotes, because all other multicellular eukaryotes have abandoned the primitive lifestyle of eukaryotes, by taking the lifestyles of either heterotrophic or phototrophic bacteria. However for both other kinds of lifestyle changes there are multiple examples, i.e. besides true fungi that are opisthokonts there are several other groups of fungous eukaryotes that are not opisthokonts, the best known being the Oomycetes. There are also bacteria with fungal lifestyle and topology, e.g. actinomycetes a.k.a. Actinobacteria. If we will ever explore other planets with life, those living beings will not have a common ancestor with the living beings from our planet, but nevertheless it will still be possible to classify them based on their lifestyle in about a half of dozen groups that would be analogous to animals (multicellular living beings that feed by ingestion, so they must be mobile or they must have at least some mobile parts), fungi (multicellular beings that grow into their food, absorbing it after external digestion), oxygenic phototrophs, anoxygenic phototrophs, chemoautotrophs, unicellular equivalents of animals and fungi, like protozoa and heterotrophic bacteria, viruses. These differences in lifestyles are more important in most contexts than the descendance from a common ancestor. So while it is useful to have the name Opisthokonta for the contexts where fungi and animals and their close relatives must be included, it is much more frequent to need to speak separately about fungi and other fungous organisms on one hand, and animals on the other hand. I agree that the term "kingdom" is obsolete when used in the context of a cladistic classification of the living beings. Perhaps it should be retained for a non-cladistic classification of the living beings, based on the few fundamental lifestyles that are possible, and which would remain valid even for extraterrestrial living beings.

deleted 2y ago

[deleted]