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Author Topic:   Is Earth old enough for DNA to evolve?
PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


(1)
Message 6 of 60 (668100)
07-17-2012 8:25 AM
Reply to: Message 1 by bcoop
07-17-2012 4:15 AM


quote:
4. The base pairs are the building blocks of DNA. If I follow evolutionary theory correctly, if there are 3 billion base pairs then it took 3 billion replication errors to arrive at the current DNA structure ( unless multiple simultaneous positive replication errors occurred).
The issue you raise here is length. Evolutionary theory does not claim that the genome increases in length by a single base at a time. A single gene duplication event would typically add thousands of bases.
quote:
5. If there was a successful DNA replication error each generation then it would take 3 billion reproductive generations to arrive where we are today.
Problems:
a. 3 billion generations would take 60 billion years if each female reproduced at the age of 20.
b. It is stated that life on earth is only 2 billion years old.
c. It would take longer if any of the errors were not advantageous. Most replication errors are not advantageous.
d. This assumes that each and every mutation was the exact necessary mutation needed in the right order. Each block of the genome has to be built in the right order. ( You don’t need the lens of the eye before the optic nerve exists for example).
e. It also assumes that each generation got the opportunity to successfully reproduce and didn’t die first or something.
f. The replication error of a single base pair out of the 3 billion pairs can result in a genetically transmitted disease. We need 3 billion positive consecutive errors with no negative errors along the way, or it would take even longer.
g. There is no provision at all here for natural selection because that would exponentially add much more time.
As has been pointed out the assumption of a 20 year generation time is absurd.
At the molecular level, especially if we consider the whole genome, neutral change dominates. There are so many neutral mutations that they are have far more effect than the positive mutations. And since a very large proportion of the genome is not under any selective constraint at all, neutral mutations will constitute a large majority of the mutations involved.
Point d) is even more wrong. To the extent that selection is relevant it is already covered by point c). It might be appropriate if you were making the argument that it is unlikely that humans specifically would evolve (an argument which has the fatal flaw that it would be true of any complex life form), but it really has nothing to do with the length of the human genome, much of which seems to be unnecessary.
Point e) seems to have the same flaws but even worse.
Point f) is likewise irrelevant
Point g) is bizarre because points c and d are all about natural selection! How can you say that you didn't take natural selection into account when you make points which do take it into account ?
Might I suggest that you take care to work out which argument you wish to make ? If you wish to focus on the length of the human genome then don't drag in points about the a priori probability of humans evolving exactly as they are now. Do research how the length of the genome increases instead of assuming that it occurs one base at a time. Try to make an informed and coherent argument. It will serve you and this forum much better.

This message is a reply to:
 Message 1 by bcoop, posted 07-17-2012 4:15 AM bcoop has replied

Replies to this message:
 Message 11 by bcoop, posted 07-17-2012 9:18 AM PaulK has replied

  
PaulK
Member
Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


(1)
Message 31 of 60 (668153)
07-17-2012 6:29 PM
Reply to: Message 11 by bcoop
07-17-2012 9:18 AM


Re: I stand corrected
quote:
again - these things are difficult to articulate - especially knowing the level of people that are reading this
It isn't difficult to realise that proposing a generation time of 20 years is grossly unrealistic. Anyone familiar with the breeding rates of animals would know that much.
quote:
However, it was probably a child that said the king had no clothes on. I believe that asking the question how long did it take to generate the human genome is a legitimate one, and I am not really seeing a lot of answers to that so far.
It is also wise to know your limits. Trying to propose an answer to the question - as you did - without a sound basis for doing so is different from asking the question. And it is that piece of folly that has attracted criticism.
It is all very well to say that the math has to work - but the main reason why your math didn't work is because you didn't have a sensible (or even coherent) model OR sensible values for the parameters.
Now I am not going to propose a model because that is beyond my expertise. But I hope that my posts have at least demonstrated that the issue is far more complex than you thought.

This message is a reply to:
 Message 11 by bcoop, posted 07-17-2012 9:18 AM bcoop has replied

Replies to this message:
 Message 36 by bcoop, posted 07-17-2012 8:57 PM PaulK has not replied

  
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