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DNA - The Wonder of Life
gemma-the-husky
Posts: 18,116 Forum Member
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Here's a serious thought.
Brian Cox's show "the Wonder of Life" the other night explained that DNA is a molecule formed from amino acids, derived from 4 basic DNA codons designated ACGT (This may not be 100% accurate - however, bear with me)
so on earth carbon based life develops, using such DNA
Now lets assume that carbon based life can only develop in this way, with DNA, and therefore has to be formed from amino acid chains, wherever it is to be found. I think this is reasonable - the special spiral feature of DNA is what allows for reproduction. It may also be unwise to "humanise" everything, but diploid reproduction appears to be a reasonably efficient process of allowing variation and selection.
point 1 -
so could it not be that apes and humans are not really "related", and in fact the species just reflect a generally similar DNA sequence, which sequence necessarily displays in similar anthropomorthic features. Hence no "missing link", rather just an observed similarity.
point 2.
Let's take this further. If we then posit that carbon based life is likely to be a common form of life in the universe , (I would actually take this further and say most common, or even only - it is hard to imagine life not based on organic chemistry for many reasons) - then it follows that the same DNA will form from amino acid chains on planets in galaxies far far away, and result in life, probably similar to ours
(on the basis that if there were an alternative to DNA, we would see it here)
so according to Brian Cox's reasoning, we will share a relatedness to those life forms, but without possibly ever having shared a common ancestor.
Brian Cox's show "the Wonder of Life" the other night explained that DNA is a molecule formed from amino acids, derived from 4 basic DNA codons designated ACGT (This may not be 100% accurate - however, bear with me)
so on earth carbon based life develops, using such DNA
Now lets assume that carbon based life can only develop in this way, with DNA, and therefore has to be formed from amino acid chains, wherever it is to be found. I think this is reasonable - the special spiral feature of DNA is what allows for reproduction. It may also be unwise to "humanise" everything, but diploid reproduction appears to be a reasonably efficient process of allowing variation and selection.
point 1 -
so could it not be that apes and humans are not really "related", and in fact the species just reflect a generally similar DNA sequence, which sequence necessarily displays in similar anthropomorthic features. Hence no "missing link", rather just an observed similarity.
point 2.
Let's take this further. If we then posit that carbon based life is likely to be a common form of life in the universe , (I would actually take this further and say most common, or even only - it is hard to imagine life not based on organic chemistry for many reasons) - then it follows that the same DNA will form from amino acid chains on planets in galaxies far far away, and result in life, probably similar to ours
(on the basis that if there were an alternative to DNA, we would see it here)
so according to Brian Cox's reasoning, we will share a relatedness to those life forms, but without possibly ever having shared a common ancestor.
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Now where you've got it slightly wrong is here. You've assumed that if a completely alien extra-terrestrial life-form were to be found, and this lifeform actually had DNA that was recognisable to us as DNA, then it would be related to us. It wouldn't. It's DNA would have evolved completely separately to us and would have 0% commonality with ours. Even if this lifeform had evolved to look exactly like us, it would truly be alien.
... and the chimpanzee coincidentally managed to build a DNA sequence 99% identical to that of a human?
That's quite some similarity.
really?
POSIT?
Posit: A statement made on the assumption that it will prove to be true.
Dont see a problem in the context of the OPs post. Since the only life we know of in the universe is carbon based - its a reasonable assumption that if we were to find life elsewhere in the universe - its also likely to be carbon based.
It sounds like you are proposing convergent evolution - but for the structure of DNA, rather than the appearance of an organism.
http://en.wikipedia.org/wiki/Convergent_evolution
The problem with that proposition however is that there is far more evidence that organisms do share common ancestors - than just common structures in their DNA sequences.
RNA is single-stranded while DNA is a double-stranded helix and these have cooperating roles in the body.
DNA is organized into structures called chromosomes which are duplicated during cell division.
These chromosomes release genetic codes that will be transcribed and carried by the RNA (specifically the messenger RNA) to the ribosome.
The ribosome will then synthesize new proteins.
And on a different note, it's always amused me that genetically, we share approximately 50% of the DNA of bananas! Therefore humans are all half bananas
Anyway, sticking with DNA, did anyone catch the recent article on quadruple stranded DNA (G-quadruplexes)?
We have known about quadruple stranded DNA for a while (and are able to produce it in a lab) but not it has been found naturally in humans. It is thought that they are natural, but do play a role in cancer.
Indeed, it is why we are desperate to find something on mars. It would give us two data points.
Hence the reason we can only make assumptions based on the information we have to hand.
Life on earth isn't the only information we have. There is mounting evidence for complex carbon based molecules all over the universe - ones that we know life uses on earth.
Like I said - within the context of the OPs post and current information - the assumption is reasonable.
You appear to be making assumptions yourself - that life does/can exist elsewhere (i.e. there are actually more points on the graph). What if the graph does only consist of one point
True - but even on Mars - how they are looking for life is very much dictated by what we know about life (i.e. the types of minerals life deposits, the types of gas it emits, the types of chemicals it can metabolise etc).
Even NASA seems to be operating under the assumption that life on Mars wont be too dissimilar to that on Earth - they cant really do much else.
that's what I meant though. It would be different, even though it shared a percentage of DNA.
Hence, perhaps animals that apparently are similar to us, are similar only for the same reason. maybe we do not share a common ancestor with animals at all.
but elements are the same elements everywhere in the universe
carbon is always going to be element no 6. and organic chemistry is always going to be organic chemistry.
now - maybe a life form can obtain oxygen in a different way than breathing it - or filtering it out of water.
I think the respiration equation is so important in this respect though
C6 H12 O6 + 6O2 <-> 6CO2 + 6H20
plants take in C02 and water, and turn it into sugar (starch) and oxygen, with sunlight.
we take in oxygen and combine it with sugar to produce energy.
It is hard to conceive of anything more elegant. Which is probably why scientists expect to find oxygen and water, if they find life.
And why there is a high probablity that there is no "graph" of life forms.
Did someone buy you a wee science book for your birthday by chance?
No - I am pretty widely read.
The thought just occurred to me when watching Brian Cox the other day, and I thought it worth a serious topic discussion
Maytbe it is "risky" to "humanize" everythnig - but I find it hard to conceive of intelligent life that is not recognisably humanoid
ie - stereo "vision" (but not necessarily visible light) , dextrous manipulation skills (hands, but maybe more than 2 would be useful - maybe extra tentacles, or a prehensile tail), endoskeleton, sexual/diploid reproduction.
SF discussion about alien life
http://www.cthreepo.com/lab/physed1/
Much of the above could be attributed to an octopus -- an intelligent and resourceful animal, but an invertebrate and nothing much like a human. The only thing that has prevented them from dominating the seas is their short lifespans.
DNA strands have billions of base pairs, the chances of two similar strands spontaneously forming would be astronomically remote.
Of course, it isn't just our nuclear DNA (the DNA in the nucleus of our cells) that would have to be similar to that of chimps. Our mitocondrial DNA (the DNA that is in the mitocondria in cells, and reproduces separately and at a different pace to nuclear DNA) is also virtually identical to that of chimps. Then there are the various organisms that call us 'home', like lice that have virtually identical DNA to between humans and chimps but are not the same species.
We have intelligent life on this planet that does not conform to the humanoid blueprint (Dolphins for example).
And corvids, the aforementioned octopus, etc.
But we do know that life exists which doesn't utilise oxygen - or the generic equation of respiration that you have posted.
It has become the dominant form of energy production, common to the majority of organisms on this planet - simply because the ingredients required to drive it are readily available.
If the conditions on earth were different - its likely that another means of energy production would have become the dominant one (and in fact probably were at some point in Earths history).
(yep - I did think of that too).