Origins and Originations

November 11, 2022 11:42 PM

The Long and Winding Road to Eukaryotic Cells - "Despite recent advances in the study of eukaryogenesis, much remains unresolved about the origin and evolution of the most complex domain of life." (via)

These close metabolic associations between organisms, a type of symbiosis known as syntrophy, may have prefaced the evolution of complex life by creating alliances that turned permanent over time, [Purificación] López-García says. In this way, individuals of different microbial species could have nested within one another to create a host with one or even several symbionts. This is exactly what scientists suspect happened to form a whole new type of cell, the eukaryote, which thrived and subsequently diversified into the macroscopic array of life we see today, including humans. So-called eukaryogenesis is not defined the same way by all researchers, but broadly, the term describes an evolutionary surge toward increasing cellular complexity between 1 and 2 billion years ago.

During this time, some of the defining characteristics of modern eukaryotic cells—the nucleus, mitochondria, cytoskeleton, cell membrane, and chloroplasts, among others—made their debut. These occurred between the first and last common ancestors of all living eukaryotes, known by their acronyms, FECA and LECA, respectively. Most of the details of these evolutionary leaps, however, remain unsettled. Researchers do not uniformly agree on which branch of life eukaryotes sprang from, which microbial players might have contributed to the process, or on the order of specific evolutionary milestones along the way. But the recent identification of the Asgard archaea, thought to be the closest living relatives to modern eukaryotes, has enlivened discussions about eukaryogenesis.

Eukaryogenesis and oxygen in Earth history - "The discovery and cultivation of the Asgard archaea has reinforced metabolic evidence that eukaryogenesis was initially mediated by syntrophic H₂ exchange between an archaeal host and an α-proteobacterial symbiont living under anoxia. Together, these results temporally, spatially and metabolically decouple the earliest stages of eukaryogenesis from the oxygen content of the surface ocean and atmosphere. Rather than reflecting the ancestral metabolic state, obligate aerobiosis in eukaryotes is most probably derived, having only become globally widespread over the past 1 billion years as atmospheric oxygen approached modern levels."

also btw...

• Inside the Proton, the 'Most Complicated Thing You Could Possibly Imagine' - "The positively charged particle at the heart of the atom is an object of unspeakable complexity, one that changes its appearance depending on how it is probed. We've attempted to connect the proton's many faces to form the most complete picture yet."
• Andrej Karpathy: "So somehow, I have no idea how, evolution has found a way to encode these algorithms -- and these neural net initializations that are extremely good -- into ATCGs, and I have no idea how this works, but apparently it's possible because here's a proof by existence. There's something magical about going from a single cell to an organism that is born..."
• @ben_golub: "During the Neolithic Revolution, seven populations independently invented agriculture in a surprisingly narrow band of time. Why did this happen? This is an awesome thread about the mystery and a proposed resolution."

posted by kliuless (7 comments total)

Ah, sweet mystery of life, at last I've found you
posted by nofundy at 5:58 AM on November 12, 2022 [4 favorites]

To throw in a book recommendation, I recently read David Quammen's The Tangled Tree. After reading a lot of Stephen Jay Gould and Richard Dawkins and folks like that in my youth, I knew that there was a lot of evolution that was still under contention, but until Quammen's book I hadn't realized just how fundamental the shifts in our understanding had been, and that the idea of one species gradually arising from another is in some ways just a myth, a simplification that has little bearing on the genetic jumps from species to species, as life just goes barreling ahead. The idea that eukaryotes could arise from smaller, simpler creatures mashing themselves together and cooperating becomes a lot less outlandish when you realize the barrier between those creatures--the barrier between what defines one of them as different than the other--is extraordinarily porous. (I'd always thought of the archaea as just another kind of bacteria, and so this was all amazing and new to me.)
posted by mittens at 6:19 AM on November 12, 2022

Lynn Margulis faced a shitstorm of ridicule when she developed the endosymbiotic theory in 1967 (then writing as Lynn Sagan, yes that Sagan).

By now the origin of chloroplasts and mitochondria via this route is well accepted, there's a nice special issue of the Journal of Theoretical Biology devoted to the legacy of her work, here's the introduction on Sci-hub.
posted by SaltySalticid at 6:55 AM on November 12, 2022 [3 favorites]

I took BI504 Evolution with Lynn Margulis in grad school in 1982. Practically the whole course was about what happened more than 1 billion years ago: stromatolytes; microbial mats; Mixotricha with its five microbial endosymbionts; the Entner–Doudoroff pathway; and, of course, mitochondria as reduced instruction set endosymbiotic Alphaproteobacteria. The last 600 million years of the Phanerazoic = post-Cambrian eon was knocked off in two final lectures with an insouciant "eukaryotes: plants, animals, fungi and protista are essentially the same".
posted by BobTheScientist at 7:45 AM on November 12, 2022 [4 favorites]

Cellular Biology is not really my thing, but I learned a little bit about the evolution of Eukaryotic Cells when we worked on an art project about The Great Oxidation Event, which is really interesting.
posted by ovvl at 5:08 PM on November 12, 2022

I recently read 'Power, Sex, Suicide' by Nick Lane, a book all about mitochondria. I've no background at all in biology or chemistry, but he's a fantastic writer and I was able to take away a lot.

He's a great speaker too, and I highly recommend his lectures on youtube: Why is life the way it is? is an accessible intro to the topics raised in this post.
(edit - correct book name!)
posted by kmkrebs at 8:53 PM on November 12, 2022 [1 favorite]

In 2009 I read and very much enjoyed Life On A Young Planet. I read the 2003 edition; it was updated in 2015.
posted by neuron at 7:28 PM on November 13, 2022 [1 favorite]