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1. adrian_b · 1790541762 · focus · HN ↗

   While the research about Paulinella is very interesting, it has no relationship whatsoever with "the origins of life".

   What this research is about is the origin of plants, which are indeed one of the most important forms of life, but the origin of plants is distant by billions of years from the origin of life and it is even distant by billions of years from the origin of phototrophy (frequently, but not really correctly, called "photosynthesis", i.e. the extraction of energy from solar light).

   The ancestor of red algae and green algae (the terrestrial plants are descended from green algae) has been created by the hybridization through symbiosis between a unicellular eukaryote (i.e. nucleated cell) and a cyanobacterium, a.k.a. blue-green alga.

   As explained in TFA, Paulinella is the second case of such a symbiosis between a nucleated cell and a cyanobacterium, which happened relatively recently, unlike the symbiosis from the origin of plants, which happened about a billion and a half years ago.

   Because Paulinella and its internal symbionts have not been modified so profoundly by symbiosis like the red algae or green algae, it can provide information about how the early stages of the hybridization happened, eventually allowing a better understanding of how plants function.

   1. kulahan · 1790550385 · focus · HN ↗

      Isn’t this about the origin of complex life?

      1. adrian_b · 1790577527 · focus · HN ↗

         There were several jumps in complexity, this is only one of them.

         The first jump in complexity was the appearance of the eukaryotes, a.k.a. nucleated cells, which also happened through hybridization through symbiosis of different kinds of cells.

         The event discussed in TFA was the second jump in complexity.

         After the ancestor of the red algae and green alga was created by the hybridization of an eukaryote with a cyanobacterium, eventually the cyanobacterium was reduced to a smaller cellular component named chloroplast, which is the site where solar light is captured, and a big part of its DNA has migrated into the nucleus, where it fused with the DNA of the eukaryote host.

         Probably after a few hundred million years after the hybridization event, and after the descendants have split into red algae and green algae (the former are adapted to deeper water, which is not reached by the reddish part of the solar light, while the latter are adapted to shallow water with strong light, which enabled them to also spread on the continents, in freshwater), both red algae and green algae evolved multi-cellular forms, which was the next step in increasing complexity.

         There is evidence of multi-cellular red algae and green algae from slightly more than a billion years ago. These are the most ancient living beings whose kind can be identified with certainty, because for most unicellular living beings identification is not possible without checking for features that are not preserved in fossils.

         The multi-cellular animals, which brought another jump in complexity, appeared only a few hundred million years after the red algae and green algae, in a world where there was a surplus of food from the activity of the abundant algae.

         1. kulahan · 1790644455 · focus · HN ↗

            I appreciate you breaking it down for me. I wasn't aware (though it makes perfect sense now that I'm reading it) that the capture of a foreign cell and the fusion of its DNA into the host are separate jumps, but that makes sense. I think that's where, for me at least, the confusion came in.

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