How is DNA even possible anyway?

A good question! Here's a way to help you picture it.Imagine that you were exploring at the bottom of the ocean, and you saw an arrangement of shells that looked like this:It would be hard to picture - even though all of the evidence says that there have been no other humans here - that some sort of intelligence didn't place these shells in an arch for some unknown purpose. Namely, because if any of the shells was missing, the structure would collapse. This type of argument is known as "irreducible complexity".However, the structure - while irreducibly complex in its *current form*, doesn't mean that it was always so. For example, picture a situation in which soil was layed down over time, with mollusks living and then leaving their shells behind as this happens, and then some time later, the soil erodes away: The reason that the shells can be built up is that the soil acted as a "scaffolding". Later, the scaffolding was eroded away without a trace, but the shells remained.The same can hold true with life. Almost noone proposes that the earliest forms of proto-life life were themselves DNA-based. However, when DNA came into play as a helper molecule - initially likely just tiny strands that coded for a single piece of RNA - it proved very effective (with good reason) at coding for RNA, and spread throughout the population.The standard theories for abiogenesis typically runs along the lines of (one example below):1. The amino acids naturally form in the world (and in space!), fairly widely. This much is well known, and is little contested.2. Amino acids randomly link up into proteins in some circumstances. With the scale of the earth, and ample sources of input energy, this is not unlikely. Again, this much is known.3. Proteins can often catalyze reactions. This much, again, is well known. Randomly arranged proteins will randomly catalyze reactions.4. If a certain type of catalysis tends to produce proteins that are more "like" the protein that caused it, proteins "like" the original protein will become more common in a given area.5. The more "like" the original protein that results from a reaction, and the wider the possible range of input materials, the more common it will become. Soon, you effectively have an effective self replicator, or more likely, a group of molecules that work together to replicate each other. This is known as a "hypercycle".6. Any hypercycle that can poison off its competitors without hurting itself will become dominant. Also, by keeping themselves more concentrated, they can react more frequently. This leads to the slow progression of "walling off" of hypercycles. This stage is usually known as an "ur-cell", "protocell", or other such terms.7. The more efficient an ur-cell functions, and especially *adapts*, the more dominant it will become. DNA and RNA are both excellent for both of these functions, so they start to take over from self-replicating or group-replicating proteins. You end up with normal (albeit simple) cells that steadily increase in complexity as they compete with each other - more proteins being coded for in the DNA and/or RNA.This message has been edited by Rei, 09-23-2004 03:18 PM

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"Illuminant light,
illuminate me."

quote:

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Who thought it up?

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M. Eigen and P. Schuster. You can read more about it here. The initial hypercycle proposal involved RNA, although we don't know for sure that the first stable cycle involved RNA (that very well could have occured at the protocell stage, after the hypercycles are walled off), but we really don't know. Unfortunately, hypercycles and protocells don't fossilize ( *darn!!* )

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"Illuminant light,
illuminate me."