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If you think that early animals started out simple and gradually evolved new features, and things like sponges branched off before the new features were added, you wouldn't be alone. Over the years, lots of researchers argued the same thing. But a recent genome sequence indicated that the oldest branch of the animal family tree that led to the comb jellies, with muscles, nerves, and tentacles, were an older branch than sponges. Now with a new paper on the comb jelly, researchers are starting to argue over what this actually tells us about the earliest animals.
The comb jellies' genome contains a variety of other indications that they are exceptional. Most of the innate immune system, which broadly recognizes pathogens like bacteria and viruses, is missing. So is the machinery that processes micro RNAs, which are used to control the expression of other genes. Key regulators of development, like hedgehog and JAK/STAT proteins, are also absent. So are key genes involved in the formation of muscles, suggesting that these, too, may have evolved separately in the ctenophores.
(Score: 2) by frojack on Saturday May 24 2014, @07:09PM
The question in my mind is why virtually ALL life on earth is the controlled by the same mechanism (DNA). Why did no other form ever happen, (or arrive on space debris)?
Alleged Arsenic based life forms debunked [nationalgeographic.com]. But even those forms of arsenic tolerant life forms used DNA.
The single most successful form of life on this planet is DNA and it appears to be the only form of life on the planet.
No, you are mistaken. I've always had this sig.
(Score: 2) by Joe on Saturday May 24 2014, @09:52PM
As far as I know the main reasons why all life contains DNA are: it is great at storing information, it is structured in a way that enables faithful replication, and it is very stable. RNA is very close, but it fails to compete with DNA when it comes to stability. This is one of the reasons that RNA has an upper-cutoff of around 30,000nts in length (Coronaviruses, such as SARS and MERS, have RNA genomes in this range).
The question really depends on your definition of life: DNA is obvious since all cellular life uses it, RNA can be used as viral genomes, and amino acids (that make-up proteins) can maintain structural information and prions can propagate that information.
- Joe
(Score: 2) by frojack on Saturday May 24 2014, @11:46PM
You are still thinking inside the box.
If DNA wasn't good at its job, we probably wouldn't be here.
But there is no reason to assume it is the ONLY mechanism that could provide the same functionality.
No, you are mistaken. I've always had this sig.
(Score: 2) by tathra on Saturday May 24 2014, @11:02PM
thats one of the questions thats still unanswered by science. dna isnt really a lifeform though, its the 'source code' for life. saying that dna is a life form would be like saying the 1's and 0's running computers are a life form (not a perfect analogy, but you get the idea).
amino acids naturally form in the void of space, but its still unknown how dna came about, or if there was a precursor like tna [wikipedia.org].
something i'd like to know is if there's some natural preference for "left-handed" isomers of amino acids (leading to "right-handed" sugars) or if it was just random chance. if it was random chance, when we meet alien life forms, its likely that we wont be able to exchange foods since there would be no nutritional benefit if all life on their planet uses "right-handed" amino acids, but at least we could rest easy since they couldnt eat us for exactly that reason, and enslaving us would be too costly since they'd have to grow our food to support us.
(Score: 2) by lubricus on Saturday May 24 2014, @11:05PM
....is that life arose one and is all related.
The answer is that: ... There is no 2 for DNA specifically, although there are arguments for 4 bases (ATGC, as opposed to 2 or 6), and for the 3-base codon (as opposed to more or fewer), but those always seemed like just-so stories to me.
1. Not *all* live uses DNA (think retroviruses or prions... which probably arose from DNA based life)
2.
The simple answer seems the best.
... sorry about the typos
(Score: 2) by lubricus on Saturday May 24 2014, @11:10PM
"The complicated answer is that:"...
funny how the hands skip words that pass by the mind..
... sorry about the typos
(Score: 2) by frojack on Sunday May 25 2014, @12:14AM
4 bases vs 6 vs 20...
You are still thinking in DNA terms. Kind of like fussing over national course threads on a bolt rather than National fine.
Its still a bolt.
Why isn't there a life form that uses rivets or glue or something totally different.
Maybe no bases, maybe crystalline structured, metals, etc.
No, you are mistaken. I've always had this sig.