While reading up on Shannon's Entropy and Information Theory today I chanced upon the term "Maxwell's Demon". A term like this i find to be irresistible, so there I went to Wikipedia to read up and holy mother of god guess what did i find...??
Before venturing further allow me a discourse on Maxwell's Demon. The second law of thermodynamics states that the entropy of an isolated system, which is not in an equilibrium, will increase over time to reach a maximum when the system attains equilibrium. But why does this happen? According to Maxwell it was because of statistical improbability. Let me elaborate, suppose there is a container with an opaque, insulating partition in between. Both partitions are filled up with the same gas; however there is no way the gases can mix or temperature change because of the partition. If the gases are at different temperatures then they will remain in the same state because this system is defined to be an isolated system.
If there was a small hole in the partition then the gases would start to mix, there would be temperature exchange and before long the gases will be in equilibrium, as would be expected by anyone familiar with second law of thermodynamics. Now instead of gases being in different temperature start with a box in perfect equilibrium. But there's a small change - we are gonna introduce the Maxwell's Demon inside the box. He is a small creature who is the gatekeeper of the hole. And he has decided that fast moving molecules are allowed to enter one compartment but slow moving molecules are not. Slowly the Demon will filter all fast moving molecules to one side of box and slow moving molecules will be on the other side. This will increase the temperature on one side of box and reduce it on the other side, entropy of the system will decrease... poof goes 2nd law.
Coming back to holy mother of god exclamation, it struck me amidst all this that my Blog actually has a game which enables player to BE THE MAXWELL'S DEMON.
The "Separate the Green and Red" game has been rechristened "Be the Maxwell's Demon". Cause essentially it represents the system described by Maxwell and while it is not an exact representation of the system (regarding speed of molecule - here its the color), in essence it can very easily describe the concept!!
To think an exercise in rigid body simulation in java could turn out to be so similar to some totally different concept all together...!! What can i say : It really did happen to me...!!! :P
P.s. : Such real life Demons do exist. Think about Dialysis membrane, membrane proteins etc. But they are ALL pseudo demons, because the systems are not perfectly isolated and the act of separation causes entropy to increase elsewhere in the universe, most of these require energy in some form or the other.
Monday, May 10, 2010
Friday, May 7, 2010
Driving Forces of Evolution
What is the driving force of evolution??
What makes one species evolve into another??
Why does evolution occur??
Is it natural selection? or is it perhaps mutation?
The points below are what I understood after a bit of reading and thinking.
Natural Selection drives evolution. Since irrespective of the repertoire of different genes present in the gene pool, if one gene is not chosen above another gene (based on some criteria) then the relative frequencies of genes in gene pool will remain the same and consequently there wouldn't be any evolution.
So clearly some gene has to get selected over another, this selection criteria is called Natural Selection.
However for Natural Selection to work there must be sufficient diversity in the gene pool itself so that some or the other gene is good enough to pass the test proposed by selection. Thus rate of mutation also is a factor at driving evolution. Its observed that viruses mutate at a higher rate and (thus?) evolve at a higher rate too.
However, mutations can either make a gene better at passing the present selection test, or make it worse at it. If they make the gene worse then it will fail the test and disappear into oblivion. But generally mutations don't cause any significant change in the capability of a gene to pass a selection test. These 'neutral' mutations can accumulate to a large number over the span of time. Random drifts in such neutral mutations can result in some gene being replaced by another as result of random event. Might seem a little far fetched, but in the timescales that evolution works under its definitely plausible. And so random drifts in neutral mutations may drive evolution too.
Is there any bias for or against some particular mutation? Is it more likely for an 'A' to convert into 'G' or 'C' rather than a 'T'. Or for that matter any other combination of 'ATGC' in the above sentence. I don't know if such bias is proven, but this bias has been implicated as the reason for the observed GC content variations among closely related prokaryotic species.
Of course all these mechanisms are not mutually exclusive w.r.t gene or time. For different genes different factors would be responsible for evolution. But these forces probably are the reason why one species evolves into another with passage of time.
What makes one species evolve into another??
Why does evolution occur??
Is it natural selection? or is it perhaps mutation?
The points below are what I understood after a bit of reading and thinking.
Natural Selection drives evolution. Since irrespective of the repertoire of different genes present in the gene pool, if one gene is not chosen above another gene (based on some criteria) then the relative frequencies of genes in gene pool will remain the same and consequently there wouldn't be any evolution.
So clearly some gene has to get selected over another, this selection criteria is called Natural Selection.
However for Natural Selection to work there must be sufficient diversity in the gene pool itself so that some or the other gene is good enough to pass the test proposed by selection. Thus rate of mutation also is a factor at driving evolution. Its observed that viruses mutate at a higher rate and (thus?) evolve at a higher rate too.
However, mutations can either make a gene better at passing the present selection test, or make it worse at it. If they make the gene worse then it will fail the test and disappear into oblivion. But generally mutations don't cause any significant change in the capability of a gene to pass a selection test. These 'neutral' mutations can accumulate to a large number over the span of time. Random drifts in such neutral mutations can result in some gene being replaced by another as result of random event. Might seem a little far fetched, but in the timescales that evolution works under its definitely plausible. And so random drifts in neutral mutations may drive evolution too.
Is there any bias for or against some particular mutation? Is it more likely for an 'A' to convert into 'G' or 'C' rather than a 'T'. Or for that matter any other combination of 'ATGC' in the above sentence. I don't know if such bias is proven, but this bias has been implicated as the reason for the observed GC content variations among closely related prokaryotic species.
Of course all these mechanisms are not mutually exclusive w.r.t gene or time. For different genes different factors would be responsible for evolution. But these forces probably are the reason why one species evolves into another with passage of time.
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