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Daddy4UdderSlut -> RE: God, Darwin, and Kansas (8/15/2006 3:33:04 PM)
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quote:
ORIGINAL: seeksfemslave
Daddy am I right in saying that a FUNDAMENTAL tenet of natural selection is that only those changes that confer advantage, will, when exposed to environmental pressures, take hold in a species and ultimately give rise to new species.
Well, certainly fitness/reproductive advantages are more likely to be propagated than disadvantages... but actually, either can be propagated forward, as well as the "null variations" that are neither advantages nor disadvantageous. If you want to think about a genomic trajectory over time, a null variation or a disadvantage may be an intermediate to an advantage. Additionally, advantages can be snuffed out by bad fortune - superior or not, the "new model" gets killed.
You are thinking of this in dichotomous fashion - ie, either it's completely random, or, it's completely deterministic, but both of those extremes are wrong. It's a combination of both. If you want an example of a different type of optimization that occurs in nature that has nothing to do with evolution, and also contains deterministic and stochastic components, read on annealing:
http://en.wikipedia.org/wiki/Annealing
In annealing, the "particles" of a system move about totally randomly, as a result of thermal energy, see:
http://en.wikipedia.org/wiki/Brownian_motion
... yet, as the system is cooled, the final state of the system will invariably lie at lower energy than the initial state, before an annealing cycle. How can that be possible, if they are just random motions - how they can always produce a better result then? Is an Intelligent Hand guiding the atoms? You guessed it... ehhh, no. What happens is, that although the directions of the motions are random, they are more likely to be completed (and retained) if they lead to a lower energy. That is because the purely random kinetic impulses due to temperature are carried out on a backdrop of nanoscale attractive and repulsive force fields. They all move independently, and randomly, and yet the ensemble tends towards lower energy. As the temperature is lowered, the random kinetic impulses become weaker, and the atoms tend to settle into lower energy arrangements.
quote:
ORIGINAL: seeksfemslave
If yes then it is clear, looked at from the numerical point of view ,asexual reproduction produces more offspring than sexual reproduction. The X in my example was the species number NOT one of the species. Since quantity is more advantageous from the survival viewpoint why did sexual reproduction come into being under the influence of Natural Selection.
ie in asexual populations X can reproduce.
in sexual populations only X/2 can reproduce. Catch my drift ?
Lady Ellen it is no use stating the advantages of each method of reproduction WHEN THEY EXIST. The big question is how did they come into being.
Well, I think that the advantages and disadvantages of each are certainly interesting. I don't know, but at this point, I don't believe a detailed phenotypical progression has been assigned to the appearence of sexual reproduction over evolutionary time. What I do know is that sexual reproduction is observed even in some very primitive eukaryotic organisms, and has been established in ancient organisms (~ 1 billion years ago). In the older prokaryotes (organisms without even a nucleus, e.g., bacteria), there is also the related process of bacterial conjugation. So... while the whole story isn't there, we do know of a long history, and of increasingly sophisticated implementations, if you will, of sexual reproduction.
The fact that we don't know all the answers right now for evolutionary history, is in no way contrary evidence for evolution. Just as if you are doing your own personal geneology tree, and there are some unknown ancestors, missing links, if you will, that doesn't suddenly invalidate the whole concept of heredity and imply that you were brought by the stork! It's just wrong logic to think that way.
... D4US
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