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It's a bit extreme to make that leap. Multi-cellular life only emerged on Earth ~600 million years ago, after the supposed habitable period of Venus. It's unc
by lumost 6y ago
It's a bit extreme to make that leap. Multi-cellular life only emerged on Earth ~600 million years ago, after the supposed habitable period of Venus.
It's unclear for how much of the 4.6 billion year history of the earth multicellular life could have emerged and just how improbable the evolution of multicellular life is.
There are certainly events such as the symbiosis of mitochondria which appear to have occurred only once in the history of life on earth.
- andrewflnr 6y agoComplex multicellularity and cellular endosymbiosis have both occurred multiple times on earth. Those aren't the hard part. Further, there's no reason to assume that having mitochondria (rather than just having an intrinsically more efficient metabolism) is optimal, much less necessary, rather than a path-dependent accident of Earth eukaryotes.
- zabzonk 6y ago> both occurred multiple times on earth Citation?
- vmception 6y agoAny Biology & Ecology 101 book from the last decade and a half.
- zabzonk 6y agoProvide a link to one.
- mannerheim 6y agoThere are several kingdoms with multicellular life. Plants, animals, most fungi, some protists (many protists are more closely related to animals, fungi, or plants than they are to each other for that matter). See: https://en.wikipedia.org/wiki/Eukaryote#Five_supergroups https://en.wikipedia.org/wiki/Eukaryote#Five_supergroups Note e.g. that animals and fungi are closely related on this diagram, but there are unicellular fungi (notably yeast). I would guess that this means the common ancestor between animals and fungi would have been unicellular. At any rate, both are far from plants, and other protist species unrelated to all of these are multicellular. Endosymbiosis is generally accepted to also have occurred with chloroplasts. I believe there are also contemporary observed cases of protists consuming photosynthetic organisms and becoming immobile.
- andrewflnr 6y agoCheck out the abstract of this paper: https://www.pnas.org/content/99/18/11558 https://www.pnas.org/content/99/18/11558 It takes for granted not only the long-established belief that chloroplasts were once free-living blue-green bacteria, but a number of eukaryote-within-eukaryote endosymbioses. As for multi-cellular life, plants, animals, fungi, and {brown,red,green} algae independently developed it: https://en.wikipedia.org/wiki/Multicellular_organism https://en.wikipedia.org/wiki/Multicellular_organism This seems like a good article that describes the multicellularity problem in general, several interesting borderline cases, experiments in inducing the evolution of simple multicellularity (in one case, just by introducing predators into a culture), and ideas as to why it took as long as it did: https://www.sciencemag.org/news/2018/06/momentous-transition-multicellular-life-may-not-have-been-so-hard-after-all https://www.sciencemag.org/news/2018/06/momentous-transition...