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ndjokovic
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Hi, I just want some explications about the nature of "Natural Selection" in term of physical laws acting on molecules. In other words, how exactly "Natural Selection" acts on molecules and atoms.
ndjokovic said:Thanks for these explications, I am sorry, but it seems like you didn't hit my point. I mean an organism is made of the same atoms you find on the ground, all the atoms are affected by the same physical laws. I just didn't find an exact description of what makes molecules in organisms behave differently from molecules in the dust.
Following you point of view, that means that Natural selection did not act on the formation of the first cell for example.
Yes, and the reason why was answered already: the selection happens by the mutation either making the organism better or worse at reproducing.ndjokovic said:I mean random mutations happen, but Natural Selection selects mutations that help survival and reproduction, that's what I know about natural selection, am I right first?
There is only one set of laws of the universe and everything has to follow them.I just didn't find an exact description of what makes molecules in organisms behave differently from molecules in the dust.
Correct: natural selection is what makes organisms evolve - so it isn't what created the first organism.Following you point of view, that means that Natural selection did not act on the formation of the first cell for example.
Ygggdrasil said:Ah, okay, I think I understand your question now. Essentially, you are asking how do molecules and atoms form life, right? As pythagorean said, the process by which a collection of chemicals can become a self-replicating, evolving, living system is called abiogenesis. How abiogenesis occurred on Earth is not well understood, and although there are many theories about what steps may have been involved and how those steps could have happened, there is no general conensus around the issue yet. Here is a nice, simplified description of what could have happened: http://evolution.berkeley.edu/evosite/evo101/IIE2bDetailsoforigin.shtml
Now, in my previous post, when I said that natural selection operated on the level of population of organisms, I was discussing that in the context of modern day natural selection. In the early prebiotic Earth, before life had emerged, it is likely that natural selection did act on molecules. The basic rerequisites for natural selection to occur are:
1) A self-replicating system that,
2) has traits that can be passed on to its descendents, and
3) lives in an environment where certain traits allow some individuals to reproduce more than others
So, in order for a molecule to undergo natural selection, it must be able to replicate itself and its ability to replicate must be heritable. Researchers have indeed been able to engineer molecules with these properties and, when placed in the right environment, they undergo natural selection in the lab:
Joyce and Lincoln sought to evolve their molecule by natural selection. They did this by mutating sequences of the RNA building blocks, so that 288 possible ribozymes could be built by mixing and matching different pairs of shorter RNAs.(http://www.newscientist.com/article/dn16382-artificial-molecule-evolves-in-the-lab.html#.UyXF3YV7Q9s)
What came out bore an eerie resemblance to Darwin's theory of natural selection: a few sequences proved winners, most losers. The victors emerged because they could replicate fastest while surrounded by competition, Joyce says.
See also Lincoln and Joyce. 2009. Self-Sustained Replication of an RNA Enzyme. Science 323: 1229. doi:10.1126/science.1167856.
For more on efforts to build living systems in the laboratory see http://www.nytimes.com/2011/07/28/science/28life.html
Now, are these self-replicating RNA molecules alive? That very much depends on how one defines life (usually, the ability to metabolize – to harvest energy and building blocks from the environment – is considered a halmark of living systems and these RNA enzymes lack this ability). But this brings up a broader question: what makes "living" molecules different from "non-living" molecules.
Here, pythagorean again has stated the answer. Life is a property that comes about not from the molecules themselves, but from the interactions between the molecules – it is an emergent property of a collection of molecules. If you are mathematically inclined, here's one way to think about it. Consider a system of coupled non-linear differential equations. These differential equations might describe different interactions between molecules in a living system. Now, depending on the parameters of that set of differential equations, the system will behave differently. For some sets of parameters, the system will tend toward attractor points whereas for other parameters, the system will diverge away from repellor points. The system might enter a limit cycle and display oscillatory behavior for some parameter, while other parameters will lead to a chaotic system. These behaviors all depend on the initial values of the parameters of the system, the point in phase space at which these systems begin. Life, in this somewhat simplified view, is the region of phase space that allows the system to exist as a self-replicating system that can extract energy and building blocks from its surroundings. All you need to do is to find the right collection of molecules (i.e. the right set of differential equations) and set them up at the correct point in phase space, and you can create a living system.
This is what I call biased action, why selecting the mutations that help survival over other mutations ?russ_watters said:Yes, and the reason why was answered already: the selection happens by the mutation either making the organism better or worse at reproducing.
ndjokovic said:This is what I call biased action, why selecting the mutations that help survival over other mutations ?
ndjokovic said:The problem is the correct initial values is almost impossible in a stochastic point of view, and even if we assume that the correct first spark exists, and that a good soup of amino acids also exists at the good place at the good time, it would be so unstable, that a tiny tiny perturbation, a simple photon can destroy the whole machinery of the forming cell, by knocking off an electron and collapses everything.
The need of an intervention of natural selection at this stage is a must to guide this sensitive unstable process.
ndjokovic said:The problem is the correct initial values is almost impossible in a stochastic point of view, and even if we assume that the correct first spark exists, and that a good soup of amino acids also exists at the good place at the good time, it would be so unstable, that a tiny tiny perturbation, a simple photon can destroy the whole machinery of the forming cell, by knocking off an electron and collapses everything.
I'm not sure what you mean here. Natural selection at the molecular level is really just a case of continuing to self-replicate or not. If a mutation comes along that makes the process more efficient, then the more efficient self-replicators are more likely to do so and so you end up with more of them.The need of an intervention of natural selection at this stage is a must to guide this sensitive unstable process.
That's good, I think I get this step. I understood that it is a gradual random cumulative process, RNA molecules which had bad mutations collapses, and other which had mutations that do not stop the replication power continue to replicate. But I see a lot of obstacles here:Choppy said:I think you're right.
In fact if you're talking about abiogenesis, it's quite possible that many of the first complex molecules that came together with the potential to self-replicate were destroyed before they ever did. A self-sustaining chain may have been highly improbable. But the thing is, it only had to happen once. And current thinking is that it happened in stages:
(a) prebiotic synthesis of nucleotides
(b) prebiotic synthesis of polynucleotides
(c) emergence of RNA molecules capable of catalyzing their own replication
(d) evolution of the replicating RNA favouring efficiency
(e) emergence of other catalytic RNA molecules
At some point all of this gets enveloped in a lipid envelope allowing for some insulation from the outside world and from what I understand there is a kind of chicken or egg debate on when this happened.I'm not sure what you mean here. Natural selection at the molecular level is really just a case of continuing to self-replicate or not. If a mutation comes along that makes the process more efficient, then the more efficient self-replicators are more likely to do so and so you end up with more of them.
ndjokovic said:1-The need of a huge soup of amino acids in a very short time, a time shorter then the disintegration of the RNA molecule. Kind of giving food (nucleic acids) to RNAs quickly before they lose the replication power by nasty mutations.
2-A lot of mutations will destroy a lot of RNAs or stop their replication power. That needs the healthy RNA to stay in the soup.
3-Assuming the conditions 1 and 2 remains, lot of RNAs with different mutations survived and replicating well, after time this will create a random cumulative tree, but how the complex molecular machines appeared from this random cumulative tree.
Natural selection is a process by which certain traits or characteristics become more or less common in a population as a result of their impact on an organism's survival and reproduction. It is a key mechanism of evolution.
Natural selection works by favoring individuals with certain advantageous traits, which make them more likely to survive and reproduce. These traits are then passed on to future generations, leading to a gradual change in the characteristics of a population.
There is a wide range of evidence that supports the theory of natural selection, including the fossil record, comparative anatomy, and molecular biology. The observation of natural selection in action, such as in the evolution of antibiotic resistance in bacteria, also provides strong evidence for its validity.
No, natural selection is not the only mechanism of evolution. Other mechanisms, such as genetic drift and gene flow, also play a role in driving evolutionary change.
Yes, natural selection can be observed in humans. For example, the evolution of lactose tolerance in some populations is a result of natural selection, as it provides a survival advantage in societies where dairy products are a major food source.