# Evolution and DNA

1. May 17, 2015

### MaterSammichM

Does DNA exist in all living things...Humans, extremophiles, plant life?

2. May 17, 2015

### phinds

Have you done any research on this or is asking the question here the extent of your interest in researching it? I know zero about biology and a little really quick research (maybe 3 seconds) gave a clear answer.

3. May 17, 2015

### MaterSammichM

Phind, I just like to try and fit together pieces of the puzzles in my head. I don't do this for a living. I wonder things like, "If the theory of evolution is correct, do all living things have similar strands of DNA...why did we evolve as humans instead of palm trees?"

4. May 17, 2015

### Bandersnatch

MaterSammichM, all phinds is saying is that the answer to the particular question in the OP can be very easily found. You don't need to be a professional to do that.
From Wikipedia:
'DNA is a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses.'
Wikipedia is generally a reliable first-look source in scientific matters such as this one. Which is to say, if one doesn't know anything about a subject, it'll give you a fine overview on which to base further research.
It's also more efficient to ask questions about a specific point in this kind of generally-available articles, that you're struggling with, than asking broad or easily researchable questions.

Having said that, from your follow up post I can see that some clarification might be already necessary. That all living organisms have DNA coding their genetic information simply means that they all use the same chemicals to do so. It doesn't automatically imply similarity between their respective DNA strands outside this very basic fact. That is, the building blocks are the same everywhere, and this implies certain structural similarity (how the molecules bond to form a helix), but the exact arrangement as well as the number of building blocks employed varies between organisms.
How much it varies, is how you can deduce the degree of relatedness - organisms closely related will have less differences in their DNA than those further down the family tree.

As for the question you posed in post #3, the answer is no different than the answer to questions like: 'why am I me and not my cousin', 'why am I <insert skin colour> and not <another skin colour>', 'why am I a human and not a bonobo' and so on. Perhaps you can see how it's just a question of how far back you want to trace your relatedness, and how there's no other reason for the outcome than environment and chance.

5. May 17, 2015

### phinds

All the more reason to learn how to do the very most trivially simple fundamental research. Did you think my comment about finding an answer in 3 seconds was facetious? I just cut and pasted your question "Does DNA exist in all living things" into Google search and got LOTS of interesting discussion. If you can't even do this basic a level of research, how do you expect to learn anything?

6. May 17, 2015

### MaterSammichM

Yes, I can do simple, basic Google searches, but I don't trust many of the things found floating on the net, including Wiki, becase there is far too much absolute garbage out there...pure bunk.
I come here to a site with professionals, for expert opinions.

7. May 27, 2015

### Torbjorn_L

To the first question it can be added that, as Bandersnatch implies, the use of DNA show that all life on Earth do not only have common ancestry but universal common ancestry. Other early lineages, including possibly independent emergences of life, died out. (More likely the first emergence managed to spread rapidly and use all similar biochemical sources as sources for nutrients, in the manner that already Darwin figured out: existing life will extinguish emergences.)

The evolving populations that do not use DNA, RNA viruses, use its predecessor RNA that is at the core of the genetic machinery. (Elucidating that gave a Nobel Prize.)

In fact, in the sense of hypothesis testing, the observation of universal common ancestry is, due to the combinatorial nature of the topologies of hereditary trees (especially here the universal Tree Of Life), the best observation in all of science. The likelihood for a single root as opposed to multiple roots is > 10^2000! ["A formal test of the theory of universal common ancestry", Douglas L. Theobald, Nature 2010; http://www.nature.com/nature/journal/v465/n7295/abs/nature09014.html ]

As for Wikipedia it is an encyclopedia. Some of the contributors are effectively professional in what they do, and papers with statistical tests claim it is an encyclopedia as reliable as any other. (Which comes out akin to a doctor's diagnosis capability I think, some ~ 80 %.)

Furthermore it is reliable enough, used wisely, that you can see papers, expert results and sometimes opinions, from professional scientists and/or educators using it as reference. The important thing is of course that it should be used in the usual manner - if it has good references, it can be relied on not introducing too much writer's bias or making stuff up from whole cloth - and not lazily think it is all good (or all bad). [I am not giving references here, possibly introducing writer's bias. I think it is a good exercise to google around and find out if Wikipedia is a reliable source and possibly even used by scientists in some cases. It is good to be skeptical, but it is also good to find out how to learn about solid foundations for skepticism.]

8. May 31, 2015

### rootone

Everything we consider to be life must be self replicating, and in all cases of life discovered on Earth that replicating is achieved by means of nucleic acid molecules.
The 'blueprint' for the organism is encoded in DNA, but the simpler RNA molcule also plays a big part in the actual chemistry of reproduction as well as other vital chemistry.
There are some instances of viruses which have no DNA, they have only RNA, but the status of viruses as 'life' is questionable.

9. Jun 1, 2015

### rootone

If you could trace back far enough you would find that both humans and palm trees have a common ancestor, which would have been a very primitive single celled organism.
However the evolution from that organism to a palm tree is completely different path to evolution of animals, mammals, and eventually humans.
A human has no ancestor which evolved palm tree specific genes, but nevertheless human DNA does contain genes that govern metabolic biochemistry in the same manner as do similar genes in plants.

10. Jun 1, 2015

### newjerseyrunner

To further show this point, if you look at certain parts of our DNA, you will find an identical set in the palm trees. A nearly identical set of genetic instructions exists in your DNA and the palm trees at roughly the same location that controls how you and it metabolize sugar, build amino acids... These functions are so basic that it evolved long before our last common ancestor split from the palms.

11. Jun 11, 2015

### Stephanus

It depends of what your definition of "living things"
Viruses have no DNA.

12. Jun 11, 2015

### Ygggdrasil

Many viruses have DNA: http://en.wikipedia.org/wiki/DNA_virus

Examples of DNA viruses include smallpox and herpes.

13. Jun 11, 2015

### Stephanus

Because there is an IMPERFECTION in the mitosis process of a cell. Tiny imperfection.
That's why the end result might not be identical to the original cell.
But that's just the beautiful thing. The nature selects those who fit (not strong) and those who don't.
And voila in 3.5 billion years (or 4?) the ultimate product of evolution is homo sapiens. With their ambition, culture, religion, greed, nuclear bomb, art, technology, etc...
There are of course plam trees as the product of evolution. Palm tree, coconut, elephant, blue whale, etc..., and some of the evolution products are asking question "Why did we evolve as humans instead of palms tree"

14. Jun 11, 2015

### Stephanus

Terribly sorry to cause misleading. I thought they only have RNA
Thank you very much for correcting me.

15. Jun 11, 2015

### Stephanus

What does this means?
$\frac{\text{single root}}{\text{more than 1 root}} = \frac{1}{1E2000}$
Or the other way around?
I mean is it very, very unlikely that we come from 1 single root or
Is it very, very unlikely that all earth come from multile ancestor?

16. Jun 13, 2015

### Torbjorn_L

Okay, it is a fair question as such - I may have written that opaquely - but the abstract of the reference is, if technical, reasonably clear:

"the model selection tests are found to overwhelmingly support UCA ... powerful statistical evidence corroborating the monophyly of all known life." I.e. the test is an observation* that puts a bottleneck of a universal common ancestor as 10^2000+ more likely than an emergence of multiple common ancestors responsible for today's diversity of life.

* If you accept bayesian likelihood tests as an equally valid basis for hypothesis testing alongside conventional confidence tests.

One can also argue what such a fantastic likelihood means. Why would the root of the universal tree be so much more easy to resolve than later branching topologies? (Well, to be fair, Theobald had to devise new methods.)

My take is that the genetic machinery congealed along the UCA lineage at the LUCA bottleneck (with potentially other lineages dead or today recognized as RNA viruses rather than putative cellular ancestors) in a unique fashion. And branching topologies should, statistically, pick up on such universal features something fiercely.

I am currently reading a lot of papers that make the alkaline hydrothermal vents, with their inherent concentration, catalysis, polymerization/RNA replication and unique chemiosmosis pathway (e.g evolution of chemiosmosis for lipid membrane protocells had to happen in such vents, even if preceded by a free living stage), the key player to provide the reasonable bottleneck. Two things had to happen, evolution of a protein replicase and evolution of chemiosmosis with impermeable membranes, before the LUCA could put its pili to rest and take up flagella respectively archaella for free swimming in the oceans.

It looks like the timing was such that the LUCA was using DNA, probably as an evolutionary response to RNA based cellular or even viral parasites, when chemisosmis had been sufficiently perfected. (Perhaps twice, but if eukaryotes are archaea as the discovery of the Lokiarchaea sister lineage implies, a change of membranes from esters (bacteria) to ethers (archaea) and back (eukaryotes) seems doable.)

Last edited: Jun 13, 2015