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Mitochondria and the origin of eukaryotes

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Re: Mitochondria and the origin of eukaryotes

#61

Post by simonh »

gus_massa wrote: post #53
simonh wrote: post #48

Earlier quoted context omitted.

The thing that only happened once on Earth and that's a prerequisite to developing complex life forms is not endosymbiosis, it's life going multi-cellular. They are not the same thing. Endosymbiosis is not identical with going multi-cellular, and it seems that all but perhaps one of the known instances of endosymbiosis didn't play any role in us going multi-cellular anyway. In fact this article makes the case that it…

Multicellularity looks relatively easy. From https://en.wikipedia.org/wiki/Multicellular_organism#Occurre... > Multicellularity has evolved independently at least 25 times in eukaryotes, and also in some prokaryotes, like cyanobacteria, myxobacteria, actinomycetes, Magnetoglobus multicellularis or Methanosarcina. However, complex multicellular organisms evolved only in six eukaryotic groups: animals, symbiomycotan fu…

It’s relatively easy once you have evolved the biochemical infrastructure to support it, but on Earth that took several billions of years to achieve. There’s no way around it, no amount of hand waving how easy it is negates the fact it took billion years of evolution to do it.

Also most of those forms of multicellularity are extremely basic, little more than tangles or sheets of cells, even after hundreds of millions of years of further evolution. That’s not likely to get to intelligent life.

Re: Mitochondria and the origin of eukaryotes

#62

Post by code_biologist »

aesch wrote: post #57
lock-the-spock wrote: post #50

An accessible and incredibly insightful read 100% on this topic is "Power, Sex, Suicide: Mitochondria and the Meaning of Life"- despite the flashy title a thorough scientific read and analysis, working through various possible arguments and teaching fundamentals along the way. My favourite book I read in the past five years or so https://en.wikipedia.org/wiki/Power,_Sex,_Suicide

I haven't read that one but after reading The Vital Question I will recommend anything with Nick Lane's name on it. There are very few people who have thought about the origin of life as deeply as he has.

Read it as soon as you have the time. It is every bit the equal of The Vital Question.

Re: Mitochondria and the origin of eukaryotes

#64

Post by code_biologist »

sonicggg wrote: post #52

Evolution did a terrible job there. So many diseases linked to mitochondrial dysfunction nowadays. We have this amazingly complex machinery, and a single point of failure, no redundancy whatsoever.

Evolution did a great job? I highly recommend reading Nick Lane's "Power, Sex, Suicide". Mitochondrial function is a complicated question. It's amazing nature makes it work at all. Two aspects he discusses:

1) Mitochondrial selection is multilayered and aggressive. Mitochondrial population selection goes on during formation of egg cells [1]. Mitonuclear compatibility is heavily selected for during ontogeny [2]. Many miscarriages are are related to mitochondrial dysfunction. Once someone is born they've already passed a high selective bar for mitochondrial health.

2) There is a tradeoff between mitochondrial selectivity and fertility. Birds have much greater energetic requirements than mammals (flying is hard) and therefore have much greater mitochondrial selectivity. This means fewer offspring though. Pigeons and rats have similar size and metabolic rates, but a pair of rats can have 80+ offspring in a year while a pair of pigeons can only manage under 20.

[1] https://www.nature.com/articles/s41586-019-1213-4

[2] https://www.pnas.org/doi/10.1073/pnas.1910141117

Re: Mitochondria and the origin of eukaryotes

#65

Post by sterlind »

simonh wrote: post #61
gus_massa wrote: post #53

Earlier quoted context omitted.

Multicellularity looks relatively easy. From https://en.wikipedia.org/wiki/Multicellular_organism#Occurre... > Multicellularity has evolved independently at least 25 times in eukaryotes, and also in some prokaryotes, like cyanobacteria, myxobacteria, actinomycetes, Magnetoglobus multicellularis or Methanosarcina. However, complex multicellular organisms evolved only in six eukaryotic groups: animals, symbiomycotan fu…

It’s relatively easy once you have evolved the biochemical infrastructure to support it, but on Earth that took several billions of years to achieve. There’s no way around it, no amount of hand waving how easy it is negates the fact it took billion years of evolution to do it. Also most of those forms of multicellularity are extremely basic, little more than tangles or sheets of cells, even after hundreds of millions…

it took at most a billion years. there may have been predecessors that were lost - the only evidence we have from that era is what made it into the DNA of surviving ancestors.

I guess I still feel like abiogenesis should be the bigger filter. we have ideas and suggestive experiments about how it happened, but nothing's come close to convincingly demonstrating how fully self-replicating life can evolve through simple steps. whereas endosymbiosis just seems to require two prokaryotes from different trees surviving in the same membrane, and it's not difficult for me to imagine a plasmid slipping in and making copies of enough enzymes to get by.

Re: Mitochondria and the origin of eukaryotes

#66

Post by chestervonwinch »

Qem wrote: post #34
alangibson wrote: post #11

Earlier quoted context omitted.

We're all just speculating given that were stuck at sample size = 1 until we develop near light speed travel. I get the convergent evolution point, but so far the story is that 1) life arose very quickly 2) then proceeded to do very little for billions of years. If that's true, then it's bad news for the possibility of complex life being common.

> 1) life arose very quickly 2) then proceeded to do very little for billions of years. This is understating the feats of unicelular life. Those tiny organisms essentially terraformed the whole planet in those billions of years, oxidizing nearly all the iron close to earth surface, burying most carbon and then pumping so much oxygen in the atmosphere that at a point it comprised 30% of Earth gaseous envelope by weigh…

I think the parent comment meant doing very little from an evolutionary perspective.

Re: Mitochondria and the origin of eukaryotes

#67

Post by maneesh »

zeroonetwothree wrote: post #32
marcosdumay wrote: post #29

Earlier quoted context omitted.

> that complex cell happend only once on Earth Well, it's quite possible that once it happens, it voids any chance of it happening again just because life filling that niche already exists. If so, it only happens once, and this says absolutely nothing about the odds of that first occurrence. > what happened once, happens all the time That's a fallacy people do all the time here when talking about exobiology. It's bas…

Most other features evolved independently several (or even many) times so this is not a good argument. It’s not as if once there was a eukaryote it instantly spread across the whole planet, taking up every ecological niche. Even today eukaryotes don’t exist in certain environments.

While no single eukaryote did what you said, eukaryotes as a whole did, to some extent, during the Cambrian Explosion

Re: Mitochondria and the origin of eukaryotes

#68

Post by maneesh »

CRUDite wrote: post #12

If we assume single celled life is common, and exists in either all star systems, or in all systems without a hot Jupiter close to the star; then given the length of time involved here before eukaryotes, can we estimate how many planets in the galaxy have eukaryotes? Or how long it will be before some do? Presumably increasing the length of time increases the probability of occurrence as would increasing the number o…

Just us if we live in a simulation

Re: Mitochondria and the origin of eukaryotes

#69

Post by XorNot »

JumpCrisscross wrote: post #47
sterlind wrote: post #35

Earlier quoted context omitted.

per the article, endosymbiosis has happened a bunch of times. multiple different kinds of chloroplasts, several prokaryotes, a parasite etc. this was all when eukaryotes engulfed prokaryotes, but still, how does this mean unlikely? it seems imminently likely, since.. it happened a bunch of times. seems to me like prokaryotes evolve a strategy of engulfing others for their resources, then one day engulf a prokaryote i…

> how is this more of a filter than abiogenesis? Common chemistries get us very close to molecular systems subject to evolutionary pressure. (Simplest: RNA world hypothesis.) We are missing links. But the pathway is plausible. Chloroplasts, as you mention, are a potent counter argument. But once you have surplus cellular energy, additional endosymbiosis has a lower threshold. Based on current research, all life has a…

Or simply that success produces logarithmic returns: in the context of when this was happening, the first species to do it rapidly outcompeted all others and functionally ended exploration of the possibility space.

Re: Mitochondria and the origin of eukaryotes

#70

Post by flybrand »

lock-the-spock wrote: post #50

An accessible and incredibly insightful read 100% on this topic is "Power, Sex, Suicide: Mitochondria and the Meaning of Life"- despite the flashy title a thorough scientific read and analysis, working through various possible arguments and teaching fundamentals along the way. My favourite book I read in the past five years or so https://en.wikipedia.org/wiki/Power,_Sex,_Suicide

Yes, and read all of his books! Start w anything that seems interesting. His probabilistic approach to life sciences is wonderful and invigorating.
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