Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Mitochondria and the origin of eukaryotes

knowablemagazine.org

Post reply on HN
Print view View original

11–20 of 85 posts

Re: Mitochondria and the origin of eukaryotes

#11

Post by alangibson »

majkinetor wrote: post #5
alangibson wrote: post #2

> For billions of years after the origin of life, the only living things on Earth were tiny, primitive cells resembling today’s bacteria I've often used this "fact" as an argument against complex extraterrestrial life. Glad to see it might be wrong after all.

This is Nick Lane's argument - that complex cell happend only once on Earth (no convergent evolution) via this symbiotic accident and hence it's highly improbable if not almost impossible. As usual, people always seem to foreget that in this universe, what happened once, happens all the time and we are not special.

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.

Re: Mitochondria and the origin of eukaryotes

#12

Post by CRUDite »

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 of stars involved. Though how can we know if the event was statistically likely after that amount of time or whether we are deviations from the centre of the distribution (other than observing the quiet galaxy). Surely we can have a rough idea now of where we stand

Re: Mitochondria and the origin of eukaryotes

#13

Post by majkinetor »

alangibson wrote: post #11
majkinetor wrote: post #5

Earlier quoted context omitted.

This is Nick Lane's argument - that complex cell happend only once on Earth (no convergent evolution) via this symbiotic accident and hence it's highly improbable if not almost impossible. As usual, people always seem to foreget that in this universe, what happened once, happens all the time and we are not special.

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.

It only means that complex life is less frequent then single cell life, not that it is uncommon.

Re: Mitochondria and the origin of eukaryotes

#14

Post by JumpCrisscross »

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…

> can we estimate how many planets in the galaxy have eukaryotes?

Not yet. In the history of life on Earth, this has happened once. Knowing what we know about cellular biology, it’s stupidly unlikely. Beyond our present theories’ ability to quantify.

By the way, I think this is one of—if not the—great filters. It’s unlikely to happen, to not promptly get smote by its primordial planet’s tantrums and to get it so right it perpetuates for billions of years.

Re: Mitochondria and the origin of eukaryotes

#15

Post by griffzhowl »

alangibson wrote: post #2

> For billions of years after the origin of life, the only living things on Earth were tiny, primitive cells resembling today’s bacteria I've often used this "fact" as an argument against complex extraterrestrial life. Glad to see it might be wrong after all.

Nothing in the article contradicts that 'fact'. The question is only whether the development of eukaryotes involved other significant steps in addition to the mitochondrial endosymbiotic event, or whether the latter event was all that really mattered. In both cases, subsequent development of eukaryotes and hence multicellularity depended on the seemingly very rare endosymbiotic event.

Re: Mitochondria and the origin of eukaryotes

#16

Post by photochemsyn »

alangibson wrote: post #2

> For billions of years after the origin of life, the only living things on Earth were tiny, primitive cells resembling today’s bacteria I've often used this "fact" as an argument against complex extraterrestrial life. Glad to see it might be wrong after all.

The rise of free atmospheric oxygen and oceanic dissolved oxygen levels were almost certainly a requirement for the development of complex multicellular life. Using oxygen as the electron acceptor in respiration means far more energy can be extracted from reduced fuel molecules (sugars, fats, amino acids, methane, hydrocarbons, ammonia, etc.) than by using species like oxidized sulfur and iron, CO2, or nitrate (NO3) for that role.

This is really where the mitochondria come into play, as they allowed their host to utilize oxygen for this purpose. This can be seen by looking at modern eukaryotes that have reverted back to an anaerobic lifestyle:

> "In lineages of eukaryotes adapted to low oxygen conditions, mitochondria have been drastically reduced, functionally altered and, in one case, completely lost."

"The Origin and Diversification of Mitochondria (2017)"

https://www.cell.com/current-biology/pdf/S0960-9822(17)31179...

Hence, looking for the signature of free oxygen in the atmosphere of exoplanets orbiting distant stars is considered to be a fairly good indicator of the possibility of complex multicellular life of some sort, and at least of an active photosynthetic microbial ecosystem.

(Incidentally, the historical divisions withing academic university departments led to evolutionary biology generally ignoring the importance of early Earth's geochemistry in the evolution of life, as they saw evolution as a kind of cellular/organismal process divorced from the physical surroundings - the latter being the province of the geology department. The renewed interest in exobiology and origin-of-life research has tended to bridge this gap.)

Re: Mitochondria and the origin of eukaryotes

#17

Post by alangibson »

photochemsyn wrote: post #16
alangibson wrote: post #2

> For billions of years after the origin of life, the only living things on Earth were tiny, primitive cells resembling today’s bacteria I've often used this "fact" as an argument against complex extraterrestrial life. Glad to see it might be wrong after all.

The rise of free atmospheric oxygen and oceanic dissolved oxygen levels were almost certainly a requirement for the development of complex multicellular life. Using oxygen as the electron acceptor in respiration means far more energy can be extracted from reduced fuel molecules (sugars, fats, amino acids, methane, hydrocarbons, ammonia, etc.) than by using species like oxidized sulfur and iron, CO2, or nitrate (NO3)…

The way I read that is that developing complex life is even more contingent than 'just wait long enough'. Given what we know for sure, you need rather narrow concentrations of specific gasses at least.

Re: Mitochondria and the origin of eukaryotes

#18

Post by echelon »

JumpCrisscross wrote: post #14
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…

> can we estimate how many planets in the galaxy have eukaryotes? Not yet. In the history of life on Earth, this has happened once. Knowing what we know about cellular biology, it’s stupidly unlikely. Beyond our present theories’ ability to quantify. By the way, I think this is one of—if not the—great filters. It’s unlikely to happen, to not promptly get smote by its primordial planet’s tantrums and to get it so righ…

> Not yet. In the history of life on Earth, this has happened once.

1) That we know about.

2) Not unlike startups vs. established business, any newly emerging "eukaryotes" have to out-compete the already-evolved incumbents, which are already quite good at harnessing energy. You're much more likely to find success in business than in an entirely new evolutionary branch, though I doubt biological "gray goo" is outright impossible [1].

[1] Reverse chirality autotrophs sound like a scary sci-fi novel plot https://news.ycombinator.com/item?id=28038505

Re: Mitochondria and the origin of eukaryotes

#19

Post by anton96 »

frostburg wrote: post #8
csr86 wrote: post #4

How the children inherited the swallowed organism?

Presumably like we do - (I'm heavily simplifying the complex regulation involved) the mitochondria have their own DNA which gets duplicated when the cell prepares to undergo mitosis, then the two new cells split the results.

Does that implies that mitochondria also had to evolve at some point to detect duplication of their host cell so they duplicate at the same time?

Re: Mitochondria and the origin of eukaryotes

#20

Post by pmags »

For those interested but new to role of endosymbiosis in evolution, it's useful to keep in mind that there's strong evidence of an endosymbiotic origin of chloroplasts, another major event in the history of life. Here's a recent review article that highlights some of the key evidence and outstanding questions:

Sibbald SJ, Archibald JM. Genomic Insights into Plastid Evolution. Genome Biol Evol. 2020 Jul 1;12(7):978-990. doi: 10.1093/gbe/evaa096. PMID: 32402068; PMCID: PMC7348690.

Post reply on HN