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by Symmetry
3357 days ago
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The problem is that basic microbes only resperate over their surfaces so they have big square/cubed law limits on how large they can be and, by extension, on how complex their genomes can be. You need a hopeful monster that can run its metabolism throughout the cell to develop large genomes of the type that can support differentiated cells in multi-cellular creatures. |
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There are a quite a few creatures sitting at the boundary between unicellular and multicellular like colonial algae (https://en.wikipedia.org/wiki/Volvox) and hydra (https://en.wikipedia.org/wiki/Hydra_(genus) - I call this one "at the boundary" because you cans simply cut a piece of an adult and have the pieces heal intro 2 live adults, so "being multicellular" happened before having proper genomic mechanisms for encoding body plan and body plan related cell differentiation for this organism, for example, information pattern is all emergent based on relative position of cells - there are experiments to prove this, it's not all inference from what I said above). So there's no missing link here, you can have a pretty smooth continuum from unicellular to "proper multicellular" (like body plan with cell types differentiation encoded in genome so it can "boot up" from just one fertilized cell). Also yeasts and unicellular algae have pretty huge genomes with tons of redundancy / duplication / room to spare / room to accommodate multiple cloned copies etc..
Yeah, biologists do like to point out that there are "very clear differences" between the organisms I mentioned above, and that they are clearly separate things, because they do love their beloved classifications of things :) (god forbid one puts an organism on wrong shelf of their library)... but if you look at things more computationally/informationally, there's a lot of flexibility and no clear gaps/boundaries "down at the bottom of the tree of life"... really can't see anything that evolution would have a problem searching through, no big ridges to block gradient descent in this problem space (like there are before proper-unicellular-life-with-genetic code, despite all "RNA world" theories... that's why I'd be more inclined to think that there may be planets with life supporting condition where microbial life has not had the chance to start yet despite the requirements being there... rather than life "getting stuck" at the microbial stage)