

Last universal ancestor - shkesar
http://en.wikipedia.org/wiki/Last_universal_ancestor

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sumitviii
For anyone wondering if there were multiple LUAs:
[https://www.reddit.com/r/askscience/comments/1bjvxs/how_do_w...](https://www.reddit.com/r/askscience/comments/1bjvxs/how_do_we_know_that_there_was_a_last_universal/)

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contravariant
Doesn't the existence of multiple LUAs contradict either the word 'last' or
the word 'universal'?

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sumitviii
The possibility of 2 non-monozygotic twins having identical genes is not zero,
just astronomically low. Its the same for LUA.

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b08aa8b0dcfce
The possibility of you turning into a teapot is non-zero, just astronomically
low.

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sumitviii
Is it really possible?

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b08aa8b0dcfce
Mathematically speaking, yes, it is. The probability of _any event_ in this
universe is non-zero.

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sumitviii
Seriously? Can you point to some links?

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b08aa8b0dcfce
[https://google.com](https://google.com) comes to mind

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arh68
All I hear is _most stupendous badass of all time_ : (forgive the long quote)

    
    
      ... self-replicating organisms came into existence on this planet 
      and immediately began trying to get rid of each other, either by 
      spamming their environments with rough copies of themselves, or by 
      more direct means which hardly need to be belabored. Most of them 
      failed,... Like every other creature on the face of the earth, 
      [Godfrey Waterhouse IV] was, by birthright, a stupendous badass, 
      albeit in the somewhat narrow technical sense that he could trace 
      his ancestry back up a long line of slightly less highly evolved 
      stupendous badasses to that first self-replicating gizmo — which, 
      given the number and variety of its descendants, might justifiably 
      be described as the most stupendous badass of all time. Everyone 
      and everything that wasn't a stupendous badass was dead. 
      As nightmarishly lethal, memetically programmed death-machines 
      went, [his parents] were the nicest you could ever hope to meet....
    

[1] _Cryptonomicon_ , also found here
[http://tvtropes.org/pmwiki/pmwiki.php/Main/WorldOfBadass](http://tvtropes.org/pmwiki/pmwiki.php/Main/WorldOfBadass)

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xpda
Why is there only one "beginning of life" on earth? If life is likely to form
in earth-like conditions after a few billion years, shouldn't there be more
than one "last universal ancestor"? Does this suggest that life on other
earth-like planets may be very rare, or that ours is a unique life form for
our environment?

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kmicklas
It's very possible that life arose independently multiple times, but one group
grew fast enough to drive all the others to extinction. The life forms we
observe now almost certainly came from one ancestor due to the numerous
molecular similarities (e.g. use of the same form of DNA).

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NickNameNick
That ignores the possibility that early forms of life combined to form fitter
symbiotic life forms.

The parallel that comes to mind is the mitochondria within animal cells, they
probably originated as independent bacteria.

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jostmey
Quote from article "Note, however, that some studies suggest that LUCA may
have lacked DNA and been defined wholly through RNA".

How can anyone make this claim? Is there a single example of a living
organisms that is not DNA based? If everyone organism alive today uses DNA
then it is reasonable to assume that the LUCA was DNA based (which does NOT
preclude the possibility that life started off as RNA based). I guess that's
wikipedia for you.

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streptomycin
Fortunately, a citation is provided. I guess that's wikipedia for you.

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codemac
> For starters, LUCA may not have used DNA. Poole has studied the history of
> enzymes called ribonucleotide reductases, which create the building blocks
> of DNA, and found no evidence that LUCA had them (BMC Evolutionary Biology,
> DOI: 10.1186/1471-2148-10-383)[0]. Instead, it may have used RNA: many
> biologists think RNA came first because it can store information and control
> chemical reactions (New Scientist, 13 August, p 32)[1].

These are from the New Scientist article that wikipedia referenced. I don't
understand the references here, but hopefully someone will see this that can
help explain exactly how an organism doesn't have DNA, only RNA.

\--

[0]:
[http://www.biomedcentral.com/1471-2148/10/383](http://www.biomedcentral.com/1471-2148/10/383)

[1]: [http://www.newscientist.com/article/mg21128251.300-first-
lif...](http://www.newscientist.com/article/mg21128251.300-first-life-the-
search-for-the-first-replicator.html)

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KMag
In order to produce the proteins encoded in DNA, cells first make messenger
RNA (mRNA) copies of the information in the DNA and then the rhibosomes
translate the mRNA into amino acid sequences. So, while DNA is much more
stable than RNA, it's not obvious that an organism couldn't just get rid of
DNA, work with RNA, and deal with a higher mutation and degredation rate.
Plenty of viruses use only RNA to carry their genetic material.

There's a long-standing debate over whether enzymes or nucleic acids came
first. In modern cells, enzymes are necessary to catalyze energy-producing
reactions and other chemical reactions, and nucleic acids are necessary to
store the information necessary for self-replication. It seems unlikely that
nucleic acids and enzymes both were randomly spontaneously generated and
worked together in the first self-replicating chemical reactions. Instead,
most people have theorized that either early cells used proteins to store
information or used nucleic acids to catalyze reactions. It has been shown in
the lab that some reactions can be catalyzed by RNA.

So, the theory goes something like (1) self-replicating RNA spontaneously
arises that both catalyzes reactions and carries information (2) mutations in
some of the RNA causes it to create enzymes, which make much better catalysts
and out-compete RNA-only life (3) RNA-enzyme life mutates and starts using DNA
as a more stable storage format than RNA, making those DNA-RNA-enzyme
organisms more robust and these out-competed all RNA-enzyme organisms.

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PsykikTerrorist
The Mew of real life.

