Oxford scientists say: Looks like no other intelligent life in whole universe (but keep looking)

A couple of comments:

This was not described as a one in a billion (or billion to one) chance but a once in a million years event. Two totally different things. We have so far discovered two previous examples and now this is a third example. There maybe be more but it's unlikely there are many if that is all we have found so far. This isn't some kind of probability thing; it is simply that the Earth is around 4.5 billion years old, the first life appeared around 4 billions years ago and we've now discovered that 3 of these endosymbiosis events have occurred. So it has happened around once every billion years. This is not an observation on the chance of something happening but on the frequency of it happening.

However, the fact that, though rare, it has happened more than once is extremely significant as it indicates that once you have life there is a reasonable chance that you will eventually get complex life. But not very often; 3 or four times in 4 billion years is not a very frequent! Of course there may have been many more but they were not successful ie. they didn't produce anything particularly useful in evolutionary terms, so being unsuccessful they were eventually weeded out by evolution and we see no trace of them now. So maybe the original statement should be that a successful/useful endosymbiosis has only happened once every billion years.

I frequently see the universe being described as almost infinite or as good as infinite. The universe is nothing like infinite. It is finite. We know it is only about 13.7 billion years old and we know it does not have an infinite supply of energy or matter and will eventually suffer some sort of heat death. And to say something is almost infinite is not just a meaningless statement but really an oxymoron.
 
we've now discovered that 3 of these endosymbiosis events have occurred
How many organelles does a cell contain... and if they are not there as the result of endosymbiosis, how did they come into existence (i.e. how would a cell have created them)?

Perhaps, it would be better to think of organelles as possible results of endosymbiosis as well as possibly being created by a cell.
 
How many organelles does a cell contain... and if they are not there as the result of endosymbiosis, how did they come into existence (i.e. how would a cell have created them)?

Perhaps, it would be better to think of organelles as possible results of endosymbiosis as well as possibly being created by a cell.
That would be beyond my knowledge of biochemistry. However the article does not claim that organelles can only be created by endosymbiosis, just that in these three case that is what happened. It makes no suggestion that that is the only way in which organelles can evolve. Mitochondria and cytoplasms have, I believe, their own independent DNA whereas other organelles do not. Indicating, again I believe, the different origins ie. those two being from endosymbiosis. I would imagine the organelles to have evolved over the millions of years just like any other aspect of life.
 
Just a heads up that the piece I read on the discovery of a nitrogen fixing organelle says this is at least the 4th time primary symbiosis has happened:

The organelle is the fourth example in history of primary endosymbiosis—the process by which a prokaryotic cell is engulfed by a eukaryotic cell and evolves beyond symbiosis into an organelle.

It's also worth noting that biologists generally aren't looking for new examples, so this was something of a lucky find - suggesting that there may be more examples out there:

The discovery of the organelle involved a bit of luck and decades of work. In 1998, Jonathan Zehr, a UC Santa Cruz distinguished professor of marine sciences, found a short DNA sequence of what appeared to be from an unknown nitrogen-fixing cyanobacterium in Pacific Ocean seawater. Zehr and colleagues spent years studying the mystery organism, which they called UCYN-A.

In other words, they weren't hunting a new example of primary symbiosis, but a specific bacterium they thought they'd found a DNA strand from. It's worth underlining that we have an extremely fractional knowledge of the range of single-celled organisms out there, let alone their functions, so there may be other examples. This is especially as symbiosis is a very common function of biology.
 
This is especially as symbiosis is a very common function of biology.
I'm not sure that primary endosymbiosis is the same thing?

A symbiotic relationship where one organism lives inside the other is known as endosymbiosis. Primary endosymbiosis refers to the original internalization of prokaryotes by an ancestral eukaryotic cell, resulting in the formation of the mitochondria and chloroplasts.

Primary and Secondary Endosymbiosis (7.2)
 

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