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My understanding is that the really interesting thing about eukaryotes is their complexity, especially of their genomes and all the machinery needed to maintain

My understanding is that the really interesting thing about eukaryotes is their complexity, especially of their genomes and all the machinery needed to maintain them. Eukaryotic cells are just really complex overall compared to bacteria, tons of weird organelles all over the place. The arrival of mitochondria is kind of a red herring by comparison, in my view; we know cellular endosymbiosis has happened a bunch of times so it's not special. I'll grant my view is mainly driven by the question of how much complex life exists off of Earth, and therefore how hard/unlikely it was for Earth life to reach its current complexity. If it happened a bunch of times on Earth it's probably not a blocker, and therefore not relevant to my interests. :D Anyway, the evolutionary gradient that drove complexity in the genome is what I'd really like to know about. How it works, how it got started, why it apparently only happened once, etc.

wolverine876 5y ago
My (limited) understanding is that eukaryotes had (and still have!) a nucleus that can split into sex cells, changing the potential for evolution ... It took only 2 billion years from that to the Cambrian Explosion!
reubenswartz 5y ago
> The arrival of mitochondria is kind of a red herring by comparison, in my view; we know cellular endosymbiosis has happened a bunch of times so it's not special. The arrival of mitochondria, or the "merger" of the bacterial ancestors of mitochondria and the archea "host" was pivotal. Bacteria and archea have been around for billions of years, ~a billion years longer than eukaryotes. Only once, as far as we know, did they blossom into the complexity of the eukaryotic cell, via a very specific endosymbiotic event. Most of the bacterial DNA ended up in the (newly developed) nucleus, where, in addition to coding proteins for the mitochondria, it could also take on lots of new functions. We don't have a bunch of intermediate states between prokaryotes and eukaryotes-- it's a huge gulf that suggests a one time event that left most offspring unable to reproduce. Whether we are talking about life on earth or other worlds, this seems very, very lucky, and very relevant to your interests-- it is why we got the big complexity gradient, and why, even billions of years later, you don't have "complex" bacteria or archea.
- andrewflnr 5y ago
  > blossom into the complexity of the eukaryotic cell, via a very specific endosymbiotic event. Citation needed. There is a hell of a lot more to being a eukaryote than having mitochondria. They're defined by having a nucleus, not mitochondria, and I think that's a good definition. If mitochondria were a necessary step to modern eukaryotic complexity, it could only be by providing a bigger power budget, which could have happened lots of ways. Again, cellular endosymbiosis is common, other notable examples being chloroplasts and red algae serving as chloroplasts for brown algae. So, I'm not saying mitochondria are not important, but I don't think they were the blocker to eukaryote evolution.
  - reubenswartz 5y ago
    Eukaryote does mean "true nucleus", but all* eukaryotes have mitochondria. They only became eukaryotes via the merger. Again-- archea (and bacteria) have existed for billions of years, and never became "complex", even by unicellular eukaryotic standards, let alone multicellular creatures, except when the two got together (once, as far as we know) to form eukaryotic cells with mitochondria. For a citation, see The Vital Question: Energy, Evolution, and the Origins of Complex Life [see https://www.amazon.com/gp/product/B00OD8Z4JW/ref=dbs_a_def_rwt_bibl_vppi_i0 https://www.amazon.com/gp/product/B00OD8Z4JW/ref=dbs_a_def_r...]. I think you'll like it. (Among other things, it suggests that the nucleus itself developed because of the inflow of bacterial DNA and the need to parse out meaningless intron segments of genetic code.) Note also that the subsequent endosymbiotic absorption of chloroplasts is not a "common" event, although of course it is very important-- at least to us, as we wouldn't be here without it. * Some have lost them, when they are involved in symbiotic relationships that supply the required energy, or, as part of multicellular organisms-- for example, our red blood cells. Note that our red blood cells also lack nuclei.
    - andrewflnr 5y ago
      You're not even attempting to make an argument about why the origin of mitochondria deserves all the press it gets, just restating the intro biology story. I already know they're "the powerhouse of the cell". Biology has lots of powerhouses but only one nucleus.
estaseuropano 5y ago
> The arrival of mitochondria is kind of a red herring by comparison, in my view; we know cellular endosymbiosis has happened a bunch of times so it's not special. On the contrary! In billions of years of evolution it happened only very few times (successful), and only once really successfully. It is a rare event.
- andrewflnr 5y ago
  Chloroplasts don't count as really successful?

wolverine876 5y ago

My (limited) understanding is that eukaryotes had (and still have!) a nucleus that can split into sex cells, changing the potential for evolution ... It took only 2 billion years from that to the Cambrian Explosion!

reubenswartz 5y ago

> The arrival of mitochondria is kind of a red herring by comparison, in my view; we know cellular endosymbiosis has happened a bunch of times so it's not special. The arrival of mitochondria, or the "merger" of the bacterial ancestors of mitochondria and the archea "host" was pivotal. Bacteria and archea have been around for billions of years, ~a billion years longer than eukaryotes. Only once, as far as we know, did they blossom into the complexity of the eukaryotic cell, via a very specific endosymbiotic event. Most of the bacterial DNA ended up in the (newly developed) nucleus, where, in addition to coding proteins for the mitochondria, it could also take on lots of new functions. We don't have a bunch of intermediate states between prokaryotes and eukaryotes-- it's a huge gulf that suggests a one time event that left most offspring unable to reproduce. Whether we are talking about life on earth or other worlds, this seems very, very lucky, and very relevant to your interests-- it is why we got the big complexity gradient, and why, even billions of years later, you don't have "complex" bacteria or archea.

andrewflnr 5y ago
> blossom into the complexity of the eukaryotic cell, via a very specific endosymbiotic event. Citation needed. There is a hell of a lot more to being a eukaryote than having mitochondria. They're defined by having a nucleus, not mitochondria, and I think that's a good definition. If mitochondria were a necessary step to modern eukaryotic complexity, it could only be by providing a bigger power budget, which could have happened lots of ways. Again, cellular endosymbiosis is common, other notable examples being chloroplasts and red algae serving as chloroplasts for brown algae. So, I'm not saying mitochondria are not important, but I don't think they were the blocker to eukaryote evolution.
- reubenswartz 5y ago
  Eukaryote does mean "true nucleus", but all* eukaryotes have mitochondria. They only became eukaryotes via the merger. Again-- archea (and bacteria) have existed for billions of years, and never became "complex", even by unicellular eukaryotic standards, let alone multicellular creatures, except when the two got together (once, as far as we know) to form eukaryotic cells with mitochondria. For a citation, see The Vital Question: Energy, Evolution, and the Origins of Complex Life [see https://www.amazon.com/gp/product/B00OD8Z4JW/ref=dbs_a_def_rwt_bibl_vppi_i0 https://www.amazon.com/gp/product/B00OD8Z4JW/ref=dbs_a_def_r...]. I think you'll like it. (Among other things, it suggests that the nucleus itself developed because of the inflow of bacterial DNA and the need to parse out meaningless intron segments of genetic code.) Note also that the subsequent endosymbiotic absorption of chloroplasts is not a "common" event, although of course it is very important-- at least to us, as we wouldn't be here without it. * Some have lost them, when they are involved in symbiotic relationships that supply the required energy, or, as part of multicellular organisms-- for example, our red blood cells. Note that our red blood cells also lack nuclei.
  - andrewflnr 5y ago
    You're not even attempting to make an argument about why the origin of mitochondria deserves all the press it gets, just restating the intro biology story. I already know they're "the powerhouse of the cell". Biology has lots of powerhouses but only one nucleus.

estaseuropano 5y ago

> The arrival of mitochondria is kind of a red herring by comparison, in my view; we know cellular endosymbiosis has happened a bunch of times so it's not special. On the contrary! In billions of years of evolution it happened only very few times (successful), and only once really successfully. It is a rare event.

andrewflnr 5y ago
Chloroplasts don't count as really successful?