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I had a discussion with a friend of mine; from his understanding, bacteria and other small organisms have higher amounts of "coding" DNA and, as such, are able to evolve much faster than organisms like us. His argument was that if bacteria are able to evolve so much faster than us, then they should have become the Apex Predators on Earth instead of humans.

I argued that the 2% of the "coding" DNA is probably as long as the 90% of a bacterium (I'm guessing at this point) and that it is the bacterium's small life span that makes it evolve so fast. Was hoping to get clarification from someone with more experience in the field.

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    $\begingroup$ Well, your friends argument does indeed make no sense, which makes it kind of difficult to address. Evolution tends to drive populations to become better adapted to their environment. That in no way implies that faster evolving organisms are at the top of the food chain. Bacteria can evolve faster largely because of their short generation time. $\endgroup$ – canadianer Apr 20 '15 at 7:12
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    $\begingroup$ You can do a crude calculation about the amount of coding DNA in humans based on your 2% figure. The human genome is ~3.2 Gb. 2% of that is 64 Mb. Compare to the E. coli K12 genome which is about 4.6 Mb. $\endgroup$ – canadianer Apr 20 '15 at 7:15
  • $\begingroup$ I've heard the suggestion that DNA is encrypted as a protection against virus. Maybe someone knowledgeable here can say whether this is a serious possibility? $\endgroup$ – LocalFluff Apr 20 '15 at 13:15
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    $\begingroup$ DNA isn't encrypted... $\endgroup$ – Mithoron Apr 20 '15 at 14:55
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    $\begingroup$ Generation time is indeed the correct answer. On top of that some bacterias do exchange genetic material (like antibiotic resistance genes) via "plasmids" and therefore can adapt even more quickly. $\endgroup$ – cagliari2005 Apr 21 '15 at 7:55
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Richard Dawkins discusses this in his book The Greatest Show on Earth: The Evidence for Evolution

Bacteria and other microorganisms, specifically Archaea, are able to exchange in a sort of 'copy and paste' genetic exchange that differs wildly from sexual reproduction. They can even exchange genes with other distantly related species. This, coupled with their short (compared to Humans) lifecycle, accounts for much of the difference in evolutionary rates. Often, it makes sense to speak in terms of evolution in terms of specific genes themselves (in the case of bacteria), as opposed to evolution of the species as a whole, due to the 'copy and paste' exchange that can take place. For Bacteria, there is something to be said for compiling a 'true' family tree for each gene separately, regardless of which kind of bacteria in which it resides.

Dawkins remarks, "The philosopher Dan Dennett has put it, 'Where the tree of life for animals is a majestically spreading oak, that for bacteria is more like a banyan.'"

Also, evolution by Natural Selection and random mutation does act on 'non-coding' DNA, just to be clear.

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http://www.livescience.com/46986-human-genome-junk-dna.html

Microorganisms are often able to adapt to new environments quickly, but they lack the specialized functions of macro-organisms. Consider that the micro-organisms of macro-organisms have developed to form machinery that builds solutions to problems, rather than being retrofitted themselves to counteract new threats. Each time a bacteria needs to adapt itself to attack, whereas the specialized cells of our body can manufacture a solution on the fly rather than waiting around for a random beneficial strait to show up in the population. It would be like a small manufacturer quickly retrofitting it's production system to produce a new product. Sure, it can produce a new product, but it takes time for setup, and the company can only produce a limited number of varied products at a time, whereas a giant production company may have a huge amount of preset equipment for manufacturing a enormous variety of products with no need for retrofitting (evolution). The larger factory could have the advantage when it comes to efficient production, with quicker turnaround.

Therefore, the specialization of micro-organisms leads to nature allowing the evolution of macro-organisms as the major factories of nature.

Excess, unused (or at least non-critical) DNA is useful because it allows evolution some wiggle room. If a bacteria suffers a deleterious mutation in a vital gene, then it's obviously not fit. But, that same bacterium with can accumulate potentially useful codes in the previously unused portion of it's genome, without needing to deal with risky mutations in vital genes. And again, as microorganisms specialize, they can fabricate new proteins and such, with lower risk, and less time, compared to micro-organisms which use evolution of their genome as the sole/primary means of short term adaption.

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    $\begingroup$ This is not exactly correct.... non coding DNA is not "unused" as you said. Several studies have proven that non coding DNA, in most cases, is in fact regulatory DNA, origins of replication, centromeres, telomeres, etc.. Sources in case you're interested: theguardian.com/science/2012/sep/05/…, en.wikipedia.org/wiki/Noncoding_DNA, ncbi.nlm.nih.gov/pmc/articles/PMC2884187 $\endgroup$ – CDB Apr 20 '15 at 16:53
  • $\begingroup$ I assumed by the word "non-coding" that they meant sequences which are truly responsible for nothing. There are obviously going to be sequences that do nothing, or do something which has a completely neutral effect. $\endgroup$ – SmugDoodleBug Apr 20 '15 at 20:13
  • $\begingroup$ Also, there is an issue with the idea that all the genome is being used: livescience.com/46986-human-genome-junk-dna.html The human body is pretty complex compared to wheat. Yet wheat has 5 times the amount of information? That can't possibly all be regulatory and such. $\endgroup$ – SmugDoodleBug Apr 20 '15 at 20:26
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    $\begingroup$ Perhaps it would be better to use the term junk DNA rather than non coding DNA than, seeing as most non coding DNA actually does do something. I just wanted to clear up a term that many people get wrong. As for the wheat, it's large genome comes mostly from it's many ancestors. And yes, most of that %80 non coding DNA is regulatory and such. But you are right, not all of that is vital, but there is only a very small percentage that is actually junk. Like I said, I just wanted to clear up that term. $\endgroup$ – CDB Apr 20 '15 at 21:11
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    $\begingroup$ I never said it wasn't possible to get unused sequences, I merely wanted to clarify the misused terms to avoid confusion. $\endgroup$ – CDB Apr 20 '15 at 22:06

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