1. Originally Posted by darryl
But to claim "nature selects the fittest" is far from explaining where the "fittest" come from.
The fittest comes from natural variation.

Take a look around you next time you walk down the street.
Are all people the same height?
Are all people the same weight?
Do all people walk at the same speed?

No, of course not.

Now, if we lived in a world where there was an ever present death field that caused your head to explode, that was placed exactly six feet off the ground, then people who have a height of less than six feet become the fittest to survive.

Likewise, if there was some virus that caused people to implode into a singularity when the reached a weight of exactly 120 pounds, then people who have weights less than 120 pounds become the fittest to survive.

Finally, if there was some ubiquitous predator whose speed was limited to 3m/s that wasn't afraid of cities, then people capable of moving at speeds in excess of 3m/s would become the fittest to survive.

The other thing is, in all three of these scenarios, it's possible to disprove natural selection, because natural selection predicts that because we're eliminating the herditary traits that lead to tall people, heavy people, or slow people (respectively), that those traits should become rare, or extinct. If, however, in a few hundred generations, Holland still had as many people in talled than six feet as they do today, natural selection would be falsified.

The moral of the story is that fitness is determined by environmental pressure acting on natural statistical variation.

for the same reason that random walks lead away from the starting point, on average.

Er... your standard, vanilla random walks end up exactly at the starting point, on average. Maybe you meant something different or more specific? I don't think the usual (symmetric) random walk is a good model for a "selection," since it has no preference for any one direction over another.
They don't "end up" anywhere, and on average a random walker will be found a distance proportional to sqrrt(N) from start, where N is the number of steps. http://en.wikipedia.org/wiki/Random_walk

The selection events are modeled by the steps, and as observed need no preference for any given direction to produce evolutionary change. If there is one, then naturally the change will come faster and be larger in short times.

The inevitability of evolutionary change, given the observed variation and observed selection, was the point - the real question is what's keeping species stable over long times, what's preventing evolutionary change.

3. Originally Posted by iceaura
The inevitability of evolutionary change, given the observed variation and observed selection, was the point - the real question is what's keeping species stable over long times, what's preventing evolutionary change.
There should be a limit to everything even to environmental & lifstyle insults.

4. In view of so thought "nature balances itself" truth should lie in balance not in excess on EITHER side, positive or negative. For it, one big question arise that;

Whether evolution & natural selection is always constructive or it can also be destructive??

5. Originally Posted by Kumar
In view of so thought "nature balances itself" truth should lie in balance not in excess on EITHER side, positive or negative. For it, one big question arise that;

Whether evolution & natural selection is always constructive or it can also be destructive??
Destructive... hmmm... it cannot be either.

99.9% of species that ever existed have gone extinct. But whether an evolutionary change is advantageous or not is entirely dependent on the needs of an organism to survive in the environment it is in.

So, a wooly mammoth, well adapted to its environment would suffer and die out if the environment were to suddenly get much warmer.
...UNLESS- the species is lucky enough to have a mutation that allows a change- such as if above mentioned mammoth had a major balding gene.
Balding mammoths would suddenly have the advantage in surviving long enough to breed.

6. Originally Posted by Neverfly
Destructive... hmmm... it cannot be either.

99.9% of species that ever existed have gone extinct. But whether an evolutionary change is advantageous or not is entirely dependent on the needs of an organism to survive in the environment it is in.

So, a wooly mammoth, well adapted to its environment would suffer and die out if the environment were to suddenly get much warmer.
...UNLESS- the species is lucky enough to have a mutation that allows a change- such as if above mentioned mammoth had a major balding gene.
Balding mammoths would suddenly have the advantage in surviving long enough to breed.
Thanks.

But I was thinking that, can there be some destructive phase when nature want to destruct either to balance itself or to renew?

7. Originally Posted by Kumar
Thanks.

But I was thinking that, can there be some destructive phase when nature want to destruct either to balance itself or to renew?
No. Nature doesn't think about any of it in any way.

If you wonder about that- look up- check for rainbows.

8. [QUOTE=Neverfly;2940477]No. Nature doesn't think about any of it in any way.

[QUOTE]

If so, will big bang theory not fail?

9. Originally Posted by Kumar
Thanks.

But I was thinking that, can there be some destructive phase when nature want to destruct either to balance itself or to renew?
There are some isolated cases in which the organism undergoes change, such as genetic drift (such as when the gene pool gets too small, eg., inbreeding) and new traits develop which are maladapted to the environment. Another problem is when the habitat changes suddenly (like human caused abrupt changes) and it remains maladapted because it can't evolve fast enough.

http://www.sciencedirect.com/science...69534702025806

10. Originally Posted by Aqueous Id
There are some isolated cases in which the organism undergoes change, such as genetic drift (such as when the gene pool gets too small, eg., inbreeding) and new traits develop which are maladapted to the environment. Another problem is when the habitat changes suddenly (like human caused abrupt changes) and it remains maladapted because it can't evolve fast enough.

http://www.sciencedirect.com/science...69534702025806
Thanks again.

Do humans get some weakness or compromising in stem cell mechanism due to environmental(esp. manmade) changes which probably become a reason to it can't evolve fast enough?

11. Originally Posted by Kumar
Thanks again.

Do humans get some weakness or compromising in stem cell mechanism due to environmental(esp. manmade) changes which probably become a reason to it can't evolve fast enough?
I'm having trouble understanding your question. Are you asking whether the environment affects human stem cell potency? And then whether that affects human evolution?

I'll wait for your answer. In the mean time, here's a great presentation on stem cells I really like:

http://outreach.mcb.harvard.edu/anim...rStemCells.swf

12. Originally Posted by Kumar
If so, will big bang theory not fail?
The BBT deals with Cosmological evolution. It's not really related to this topic, if even both have a similar premise.
BBT can fail for a great many reasons... so far, it has stood up to scrutiny.

13. Originally Posted by Aqueous Id
I'm having trouble understanding your question. Are you asking whether the environment affects human stem cell potency? And then whether that affects human evolution?

I'll wait for your answer. In the mean time, here's a great presentation on stem cells I really like:

http://outreach.mcb.harvard.edu/anim...rStemCells.swf

"Are you asking whether the environment affects human stem cell potency? And then whether that affects human evolution?"

Yes I mean it.

14. Originally Posted by Neverfly
The BBT deals with Cosmological evolution. It's not really related to this topic, if even both have a similar premise.
BBT can fail for a great many reasons... so far, it has stood up to scrutiny.
Yes I also felt it afterwords. But creation, maintainance & destruction should be the basis of keeping nature in balance or to renew it if thinks become out of control. BBT also sggest all these three trinities.

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