Symbiosis as critical for anything but bacteria and archaea?

[Jean Tate]

We humans cannot live, unaided, without the trillions of bacteria and archaea (and some protists too?) which inhabit our bodies.

And the first eukaryotes may have been the result of some sort of symbiosis.

My reading tells me that we think we have some idea of when at least some of the key symbiotic relationships began, if not much about the how; we certainly have no idea of how many such have vanished ("failed experiments").

Given that, what can we say about the likelihood of complex life forming being dependent on lucky symbiotic flukes?

[Noclevername]

We can say that it happened, but with only one world and timeline to examine, I don't believe we can assign any meaningful probabilities.

[Jens]

We humans cannot live, unaided, without the trillions of bacteria and archaea (and some protists too?) which inhabit our bodies.

That is true if you are talking about mitochondria, but if you are talking about gut flora, my understanding is that they are not necessary for us to survive.


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[Colin Robinson]

We humans cannot live, unaided, without the trillions of bacteria and archaea (and some protists too?) which inhabit our bodies.

And the first eukaryotes may have been the result of some sort of symbiosis.

My reading tells me that we think we have some idea of when at least some of the key symbiotic relationships began, if not much about the how; we certainly have no idea of how many such have vanished ("failed experiments").

Given that, what can we say about the likelihood of complex life forming being dependent on lucky symbiotic flukes?

I think it is generally accepted that the first eukaryotes emerged from symbiosis between a species of archaea and a species of bacteria, and the bacteria species was the ancestor of the eukaryotes' mitochondria.

But does that mean it was a fluke?

According to a hypothesis developed by David and Buzz Baum, the conversion of a bacterium into a mitochondrion was not due to a sudden chance event, but to a gradual process:

1. There was a time when the bacterium lived outside the archaeon, but already in a mutually beneficial relationship with it, i.e. each species produced substances useful to the other, or consumed substances harmful to the other.

2. The archaeon slowly developed protrusions, which partially enveloped the bacterium. Because the bacterium received benefits from staying close to the archaeon, it had no evolutionary reason to oppose this.

3. Eventually the protrusions completely enveloped the bacterium, which in this way became an internal symbiotic partner of the archaeon.

Sources:
Paper by David and Buzz Baum
Press statement summarizing the paper

[ronin]

That is true if you are talking about mitochondria, but if you are talking about gut flora, my understanding is that they are not necessary for us to survive.


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In a way they are crucial, as they are responsible for 30% of the digestion process in the human gut. Without them you would literally have to eat 30% more to get the same amount calories, in pre-modern times this could often be the difference between life and starvation. Also without gut flora, the human body would be unable to utilize some of the undigested carbohydrates it consumes, because some types of gut flora have enzymes that human cells lack for breaking down certain polysaccharides. Gut flora also synthesize vitamins like biotin and folate, and facilitate absorption of dietary minerals, including magnesium, calcium, and iron.

The gut flora community also plays a direct role in defending against pathogens by fully colonizing the space, making use of all available nutrients, and by secreting compounds that kill or inhibit unwelcome organisms that would compete for nutrients with it. Disruption of the gut flora allows competing organisms like Clostridium difficile to become established that otherwise are kept in abeyance.

[Cougar]

Given that, what can we say about the likelihood of complex life forming being dependent on lucky symbiotic flukes?

Likelihood within what timeframe?

"...single-celled life-forms persisted alone in the biosphere for perhaps 3 billion years." - Stuart Kauffman, At Home In The Universe

On the right planets, there appears to be lots of time.

[Darrell]

We humans cannot live, unaided, without the trillions of bacteria and archaea (and some protists too?) which inhabit our bodies.

And the first eukaryotes may have been the result of some sort of symbiosis.

My reading tells me that we think we have some idea of when at least some of the key symbiotic relationships began, if not much about the how; we certainly have no idea of how many such have vanished ("failed experiments").

Given that, what can we say about the likelihood of complex life forming being dependent on lucky symbiotic flukes?

I don't think luck or flukes is an accurate way to look at it. Given what life is symbiosis was nearly without doubt going to happen. Many, many times. That any specific instance of symbiosis was going to happen exactly as it did may very well have been improbable, but that symbiosis of some sort was going to happen once life got started is as near as not to a probability of 1. The really shockingly improbable thing would have been if there were no instances of symbiosis to be found in the history of life.

[kzb]

We humans cannot live, unaided, without the trillions of bacteria and archaea (and some protists too?) which inhabit our bodies.

And the first eukaryotes may have been the result of some sort of symbiosis.

My reading tells me that we think we have some idea of when at least some of the key symbiotic relationships began, if not much about the how; we certainly have no idea of how many such have vanished ("failed experiments").

Given that, what can we say about the likelihood of complex life forming being dependent on lucky symbiotic flukes?

Certainly this was given as the reason why intelligent life in the universe is so rare, by Brian Cox on his TV series.

In support of this contention is the fact that prokaryotes were around for billions of years before eukaryotes. In other words, there was plenty of time for this symbiosis to start, but the fact is it didn't. Not for ages anyhow, and that makes it look like a an extremely unlikely random event.

But it turns out there are strong arguments against this view, it is not really an answer after all.