5 ms·

>Hierarchies [...] are often found in [natural] systems Nah they aren't. The 'tree' of life is more of a full-fledged graph and the whole kingdom-order-genus-s

>Hierarchies [...] are often found in [natural] systems Nah they aren't. The 'tree' of life is more of a full-fledged graph and the whole kingdom-order-genus-species thing is muddy and ill-defined. Most of the 'hierarchy' we find in natural systems is just our own projected deformation of much more complex relationships.

charlysl 6y ago
But how about cells organized into tissues, into organs, into systems? Particles, atoms, molecules?
- throwaway4585 6y ago
  Again, there's a lot more nuance to this. Look into the rabbit hole of cadherin/catenin or how epithelia are formed to see how a tissue is much more than a bundle of cells. This hierarchical way of thinking is only designed for humans - because it helps us think more clearly. It's a crutch when you're attempting to learn, but at some point it becomes a hindrance when you want to run.
throwaway_pdp09 6y ago
Once you get complexity past the ability to do horizontal transission, and past the point where divergent species can no longer interbreed, it pretty much becomes a tree I think. If not, please show me where 2 branches rejoin where there's no H transmission nor mutual fertility. > the whole kingdom-order-genus-species thing is muddy and ill-defined Well yes, it's somewhat an arbitrary construct for human convenience, but isn't much of the muddiness down to our limited understanding of the true relationships? Regarding "cadherin/catenin or how epithelia are formed to see how a tissue is much more than a bundle of cells." could you give a link cos this is so far outside my area I really don't know what to look for (wiki article on Catenin wasn't very revealing of your point, sorry if I missed it)
- klyrs 6y ago
  > If not, please show me where 2 branches rejoin where there's no H transmission nor mutual fertility. Viral infections modify host DNA, and can also incorporate host DNA -- this is a mechanism by which lateral gene transfer can occur between macroscopic organisms. The platypus has mammal, reptile and avian DNA, and they seem to have come about long after those branches diverged -- evidence that lateral gene transfers occur between macroscopic organisms.
  - throwaway_pdp09 6y ago
    WTF horizontal gene transfer = platypus!?!? Show me some paper on this. I mean an actual scientific paper, not a paper used to roll a yard-long spliff.
    - klyrs 6y ago
      Google is free and your aggro stance doesn't encourage me to satisfy your petulant demand.
      - throwaway_pdp09 6y ago
        Well I wouldn't normally but because you're so obviously wrong I thought I'd try. First, I can't find any reference to what you claim. The platypus is a mammal, end of, AFAICT. It has kept features from it's long evolutionary path (split off other mammals 165 million years ago) but no evidence of it being from gene-jumping I could find. eg. https://abcnews.go.com/Technology/story?id=4828261&page=1 https://abcnews.go.com/Technology/story?id=4828261&page=1 But then accidentally discovered this about gene transfer albeit in another area: https://www.sciencedaily.com/releases/2018/07/180709101216.htm https://www.sciencedaily.com/releases/2018/07/180709101216.h... "This process is called horizontal transfer, differing from the normal parent-offspring transfer, and it's had an enormous impact on mammalian evolution." For example, Professor Adelson says, 25% of the genome of cows and sheep is derived from jumping genes. OK, thanks!
      - catalogia 6y ago
contravariant 6y ago
To the best of my knowledge the tree of life actually is a tree though. Or are there known cases where two species have merged to create a new species? Okay I suppose that it becomes a DAG if you zoom into the actual ancestral relations between individual organisms (which is where things become muddy). And I guess the concept of 'species' kind of forces a tree structure upon this DAG (although not exactly, but then the biologists didn't think to use a definition that provably produces a tree, in fact being of the same species isn't even an equivalence relation).

charlysl 6y ago

But how about cells organized into tissues, into organs, into systems? Particles, atoms, molecules?

throwaway4585 6y ago
Again, there's a lot more nuance to this. Look into the rabbit hole of cadherin/catenin or how epithelia are formed to see how a tissue is much more than a bundle of cells. This hierarchical way of thinking is only designed for humans - because it helps us think more clearly. It's a crutch when you're attempting to learn, but at some point it becomes a hindrance when you want to run.

throwaway_pdp09 6y ago

Once you get complexity past the ability to do horizontal transission, and past the point where divergent species can no longer interbreed, it pretty much becomes a tree I think. If not, please show me where 2 branches rejoin where there's no H transmission nor mutual fertility. > the whole kingdom-order-genus-species thing is muddy and ill-defined Well yes, it's somewhat an arbitrary construct for human convenience, but isn't much of the muddiness down to our limited understanding of the true relationships? Regarding "cadherin/catenin or how epithelia are formed to see how a tissue is much more than a bundle of cells." could you give a link cos this is so far outside my area I really don't know what to look for (wiki article on Catenin wasn't very revealing of your point, sorry if I missed it)

klyrs 6y ago
> If not, please show me where 2 branches rejoin where there's no H transmission nor mutual fertility. Viral infections modify host DNA, and can also incorporate host DNA -- this is a mechanism by which lateral gene transfer can occur between macroscopic organisms. The platypus has mammal, reptile and avian DNA, and they seem to have come about long after those branches diverged -- evidence that lateral gene transfers occur between macroscopic organisms.
- throwaway_pdp09 6y ago
  WTF horizontal gene transfer = platypus!?!? Show me some paper on this. I mean an actual scientific paper, not a paper used to roll a yard-long spliff.
  - klyrs 6y ago
    Google is free and your aggro stance doesn't encourage me to satisfy your petulant demand.
    - throwaway_pdp09 6y ago
      Well I wouldn't normally but because you're so obviously wrong I thought I'd try. First, I can't find any reference to what you claim. The platypus is a mammal, end of, AFAICT. It has kept features from it's long evolutionary path (split off other mammals 165 million years ago) but no evidence of it being from gene-jumping I could find. eg. https://abcnews.go.com/Technology/story?id=4828261&page=1 https://abcnews.go.com/Technology/story?id=4828261&page=1 But then accidentally discovered this about gene transfer albeit in another area: https://www.sciencedaily.com/releases/2018/07/180709101216.htm https://www.sciencedaily.com/releases/2018/07/180709101216.h... "This process is called horizontal transfer, differing from the normal parent-offspring transfer, and it's had an enormous impact on mammalian evolution." For example, Professor Adelson says, 25% of the genome of cows and sheep is derived from jumping genes. OK, thanks!
    - catalogia 6y ago

contravariant 6y ago

To the best of my knowledge the tree of life actually is a tree though. Or are there known cases where two species have merged to create a new species? Okay I suppose that it becomes a DAG if you zoom into the actual ancestral relations between individual organisms (which is where things become muddy). And I guess the concept of 'species' kind of forces a tree structure upon this DAG (although not exactly, but then the biologists didn't think to use a definition that provably produces a tree, in fact being of the same species isn't even an equivalence relation).