The Possible Evolution of the DNA Molecule

May 3, 2013

Discussion by: LightSeeker

My understanding is that all living things on earth contain the DNA molecule.

As Dr. Dawkins has so eloquently revealed over the course of his studies, one can trace the evolution of lifeforms back in time to shared ancestors of simpler and simpler form on the tree of life until one reaches presumably the first lifeform from which all else has evolved.

My question is this.

Was the DNA molecule as we know it today in all its complexity present entirely in that first initial lifeform but only manifesting the simplest possible attributes of its potential or was the DNA molecule itself extremely basic in form at the outset and therefore has evolved in complexity as well to its current form in present day along with the lifeforms whose blueprint it carries within it?

In other words is the DNA molecule we know today the exact same molecule containing the same potential information that started this entire process of evolving life so many years ago?

6 comments on “The Possible Evolution of the DNA Molecule

  • 1
    Kim Probable says:

    There is a hypothesis that RNA was a precursor to DNA and the first forms of life used RNA. It can still store information like DNA, though DNA is far more stable and has some other benefits. It’s possible that it was a different kind of molecule, too.

    DNA can increase in complexity, sometimes through copying errors (during the “crossing over” phase of meiosis), but also through a process known as “jumping genes” where a gene copy will be inserted into another location within the DNA. I believe that our variety of taste buds are an example of a copying error where a gene was duplicated due to chromosome misalignment. Because the body had two copies, one copy was able to mutate because the other copy would still be there to work as normal. Those mutations in the copies allow you to have a wider range of taste – salty, sweet, bitter, etc.

    Sometimes when these mutations happen, they just render the gene inactive. Sometimes they may cause serious harm to the organism or be fatal.

    Snake venom is another example – the venom is a mutated compound that was originally a copy of something that did an entirely different job in the body.

    Plants go nuts with this sort of thing.

    It’s also possible that sometimes, when these duplications happen, problems can result as well. Copies of an entire chromosome are what lead to Downs syndrome, or Edwards syndrome (which is generally fatal).

    I’m really tired, so if any of that is weird or doesn’t make sense, here’s a website on chromosome mutations. I hope I got the information right. =)

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  • 2
    Michael Fisher says:

    You assume that the First Universal Common Ancestor [FUCA] used DNA. I would suppose that DNA wasn’t involved at all ~ far, far too complex

    We also run into the problem of defining “life”. Viruses for example are considered to be on the borderline of life because they possess genes, but they do not metabolize on their own.

    I have a fancy that there was a sea of molecular replicators which were individually less complex than a virus & would not be considered life as we know it Jim. Something like this:- Molecule A makes copies of Molecule B by “eating” Molecule G which makes copies of Molecule C which makes copies of Molecule A. Over time this chain of interactions between the various populations of molecules became more complex. The point of my proposition is that if you took molecule A & put it into another environment it would not thrive if Molecule G was not present. None of the above molecules are in any sense “alive”, but together they form a system that sustains itself & creates copies of Molecules A, B, C, etc. It would not be possible to say which was the First Universal Common Replicator ~ a meaningless question.

    None of the above molecules would use DNA

    Of the many abiogenesis propositions I favour the METABOLISM FIRST MODELS

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  • 3
    Jos Gibbons says:

    In one of his books (I think it’s The Extended Phenotype, but I’m not sure), RD discusses a hypothesis according to which there used to be only 2 bases in DNA, adenine and inosine (I think). He then explains how, on this hypothesis, it gradually took its modern form. Does anyone know an online explanation of this?

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  • 4
    Michael Fisher says:

    Article on “Metabolism first” Aug 2007:-

    Robert Shapiro [NYU], however, thinks this so-called “RNA world” is still too complex to be the origin of life. Information-carrying molecules like RNA are sequences of molecular “bits.” The primordial soup would be full of things that would terminate these sequences before they grew long enough to be useful, Shapiro says.

    “In the very beginning, you couldn’t have genetic material that could copy itself unless you had chemists back then doing it for you,” Shapiro told LiveScience.

    Instead of complex molecules, life started with small molecules interacting through a closed cycle of reactions, Shapiro argues in the June issue of the Quarterly Review of Biology. These reactions would produce compounds that would feed back into the cycle, creating an ever-growing reaction network.

    All the interrelated chemistry might be contained in simple membranes, or what physicist Freeman Dyson calls “garbage bags.” These might divide just like cells do, with each new bag carrying the chemicals to restart—or replicate—the original cycle. In this way, “genetic” information could be passed down.

    Moreover, the system could evolve by creating more complicated molecules that would perform the reactions better than the small molecules. “The system would learn to make slightly larger molecules,” Shapiro says.

    This origin of life based on small molecules is sometimes called “metabolism first” (to contrast it with the “genes first” RNA world). To answer critics who say that small-molecule chemistry is not organized enough to produce life, Shapiro introduces the concept of an energetically favorable “driver reaction” that would act as a constant engine to run the various cycles.

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  • 6
    LightSeeker says:

    Hey folks!
    This is fascinating stuff. Thanks for the input.
    Right, of course. Simple to complex. An ever expanding presumably infinite web of life once started. Assuming, of course, that it doesn’t get interrupted by untoward events like asteroid collisions or super volcanoes along the way.
    Kind of strikes a blow at the heart of Destiny I’d have to say! I suppose one could speculate that all of the myriad and infinite directions of all possible branches of life are destined to manifest eventually, given enough time…but then it’s so all-encompassing that without specificity the whole idea of Destiny kind of loses its shine.
    I love this idea of Chemical Genesis. We being some incidental offshoot of some very simple molecules bumping around in the night a long time ago. I mean it makes sense to me. It feels right. There’s a sense of humor and humility about the concept that rings true. Life, as we define it, perhaps being only one potential outcome from a particular chemical soup at a particular time. I mean who knows what the rocks are thinking?
    It’s an inclusive point of view. You’ve gotta like that. Everything is made of stuff right.
    The real question I guess is why is some of that stuff apparently conscious and how did it get that way?
    Anyway, thanks for your gems and seeds. Much appreciated.
    Thinking is definitely the best way to travel!
    Shine on…

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