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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 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.