Is there more than one DNA family tree?

Sep 12, 2013

Discussion by: MIchael

Do we know if there is more than one DNA family tree?

Did life only ever start once in one place and all other life eventually evolved from that life or did it also start independantly elsewhere and contribute to the diverse species that have lived on earth.

If life did start in more than one place are we able to distinguish between the two or more 'originators' using DNA?




18 comments on “Is there more than one DNA family tree?

  • 2
    Michael Fisher says:

    Read the below with a pinch of salt as I’m not a scientist…

    The primary nucleobases are C, G, A & T in DNA and C, G, A & U in RNA

    I recall reading years ago that there are around twenty potential nucleobases that nature could have used & it was a matter of chance that she setted on the above five [I believe there’s a lot more than 20, but most of them are unsuitable for the job because of size or physical shape etc.]. DNA using alternate bases has been constructed in the laboratory & it works. I believe there are some critters that use slight variants on the standard bases [J-base rings a bell], but clearly of common ancestry to the standard bases.

    Therefore I suppose a completely unrelated family tree would most likely use different bases. BUT if DNA with different bases WAS discovered they could STILL share a common ancestor. This is because DNA wasn’t the first replicator. DNA came about on the back of a simpler ancestor replicator ~ perhaps RNA.

    That wasn’t very helpful was it? And probably rubbish too LOL

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  • It is very unlikely we will find another line because it would have to be numerically tiny compared to the main line, and thus, would have been eaten long ago.

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  • Maybe, but probably not.

    All existing DNA- or RNA-based life follows the same code book, and shows clear signs of common genetic heritage.

    This means, in the standard view, that while life may have originated numerous times, the descendants of only one such origination remain alive today.

    An alternate view would be that the DNA/RNA code is not contingent (or, as Crick put it, a “frozen accident”). It may instead follow inevitably from the root chemical processes of life, so that multiple origins could have found the same code. If that were the case, then hybridization between any number of original life radiations would be possible. It’s even possible that organisms which today we consider descendents of a common ancestor, like bacteria and archaea, actually represent two separate lineages that acquired their common genes eons ago through horizontal gene transfer, which was surely more prolific in the deep past before elaborate us vs. them mechanisms evolved.

    The preponderance of evidence, as I understand it, favors the single surviving origin interpretation. Though the lack of complete contingency in the genetic code is also the more plausible view, from what I’ve read.

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  • AFAIK there is only one genetic origin. Even viruses share some genetic code, in either RNA or DNA form. Even though viruses are considered ‘barely alive’. They don’t even have any inner metabolism and cannot reproduce by themselves.

    Prions would be another candidate at the edge of life, as an example of self-replicating proteins.

    But as far as complex organisms like cells, prokaryotes, eukaryotes, Archaea, sponges, plants animals, Only one single tree of life has been found. There may have been others before or still, only one is known today.

    On the whole, very cool stuff.

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  • 7
    Seraphor says:

    As Thanny pointed out, possibly, but it would be incredibly hard to tell, if the two trees arose at roughly the same time that is.

    If a second abiogenisis event occured much later, then it’s extremely unlikely that it survived for very long. There are very few places on this earth you can go without being completely swamped in various kinds of life forms, it’s everywhere. That’s what life does, it uses everything it can to get everywhere it can. If another tree of life formed, it was probably gobbled up by ours right away.

    This is why it’s incredibly tricky to predict how likely or how often abiogenisis occurs. It could have been a freak accident that only happened once in this solar system in about 5 billion years, or, given the right conditions, it could happen very easily. It could have happened several times in the history of our world and been almost instantly assimilated into our own before it had a chance to get a foodhold, but it would leave very little evidence, if any at all.

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  • Alternate might use the same DNA scheme, but have almost no genes in common with the big tree.

    My guess is we will find some archaic DNA trees. Life appeared on earth so quickly, it looks like the creation of life is easy.

    The alternatives may have been all but wiped out.

    Life may have originated elsewhere, multiple times elsewhere, originated once here, or multiple times here.

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  • Another thing, we haven’t really explored the anaerobic world that much, and from what we’ve found, it’s teeming with weird life and archaic lifeforms. Also another potential candidate environment where old life with ultra-low metabolism might have survived and even thrived, would be very deep caves.

    So, so far, we only have a sample of one.

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  • 10
    Alan4discussion says:

    In reply to #5 by Thanny:

    Maybe, but probably not.

    All existing DNA- or RNA-based life follows the same code book, and shows clear signs of common genetic heritage.

    This means, in the standard view, that while life may have originated numerous times, the descendants of only one such origination remain alive today.

    Even if there were multiple examples of abiogenesis, they would not be using DNA in the early stages. DNA evolved later and is the consistent genetic code throughout all present known life.
    The evidence is that DNA based life out competed all earlier forms.
    Last universal ancestor – Wikipedia

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  • I think we should look in extreme environments. The creatures there may have evolved at a very different time in each history from our normal DNA. There are creatures that have high tolerance for arsenic, heat, cold, acid, hydrogen sulphide. We might also look for symbiosis. Normal DNA may protect the archaic DNA.

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  • 12
    AspTower says:

    I would imagine that DNA grew first from the primordial soup simply because DNA was the easiest thing that Could grow from that soup.

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  • 14
    MIchael says:

    Thanks for all the replies. Most of you seem to agree that there is only one tree of life and if life arose in more than one place that life has been consumed or edged out and that there is currently no known evidence for another type life.

    I was thinking that the idea of life starting only once in one place in the 5 billion year history of our planet might play quite nicely into the armoury of theists’ position that God created life. For me as an atheist I hope that life really did erupt more often than once. It just seems so tenuous and almost desperate that one little thing started it all and might so easily never have happened at all.

    On the other hand if we can somehow discover another thread of life or proof that life started in other places at different times then that would make the theist position that God created life a very difficult one. They would then somehow have to explain that God created life over and over again and I just don’t think the Bible, Koran or Torah contain information that could cope with that type of reality.

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  • 15
    Tearman says:

    If new abiogenisis events were occurring, their products wouldn’t have had much time to adapt to their environment. They’d probably be easy pickings for the competition. The competition being the product of a much older line, and hugely more adapted to its environment.

    Abiogenisis may be happening all the time.

    Hey, I signed up just to comment on this.

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  • 16
    Chaerephon says:

    If life did start several times on Earth or elsewhere in the Solar System, the evidence of earlier DNA/RNA or protein codes may still exist in space on material ejected in asteroid impacts, in the same way that “Martian meteorites” were ejected from the surface of Mars and later landed on Earth.

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  • 17
    Alan4discussion says:

    In reply to #13 by nick keighley:

    Yes, I find it highly unlikely that non-terrestrial life would use exactly the same DNA as terrestrial life.

    If the same DNA was found elsewhere in the Solar System, that would be more likely to be evidence of life being carried between planets after meteor impacts.

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  • If you look at the details of the genetic code – that is the code translating DNA via RNA to Protein, it is almost impossible to believe that there could be any guiding rule that caused multiple separately originated lines of life to home in on the same code. Therefor the evidence points at only one origin, at least from the establishment of the genetic code onwards.
    The code is, by the way, not universal.

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