Re: DNA sequence space

From: Pim van Meurs <>
Date: Sat Oct 01 2005 - 16:12:40 EDT

Dr. David Campbell wrote:

>>Ah, need to be careful. Again, NS guides nothing, all it does is kill
>>off the bad designs.
>It guides in two ways:
>Mutations are random in the sense that the probability of any
>particular mutation occurring is expressed by a probabilistic rather
>than a deterministic model (as far as we can measure-this doesn't prove
>anything about God's determining of the results). However, the
>probability that mutation X versus mutation Y occurs may differ
Yes David, you have understood that which so many people fail to appreciate.

> Past natural selection would affect what parts of the
>genome are more or less prone to mutation.
Yes, and even what mutations are more likely to arise. In other words,
evolution affects its own ability to evolve in that it selects from past

>Also, certain conditions
>may favor increased or decreased mutation rates in general. E.g., heat
>shock proteins help stabilize other proteins and thus hide the effects
>of mutations. If the cell encounters significant stress, the heat
>shock proteins may take up other damage control functions, allowing the
>previously hidden mutations to have an effect.
Another excellent example as to how evolution can select for mechanisms
which affect mutations.

>Natural selection also constrains the portion of the sequence space
>that is reachable by mutations.
Once again, excellent.

>E.g., regions of the sequence space
>that automatically kill the organism that reaches them will not be
>further explored once they are reached. An analogy would be if I were
>to attempt to find the door of this room by walking around randomly
>with my eyes closed. The walls and furniture prevent me from trying
>certain routes. Thus, my search will not be a full random search of
>the space of the room.

Hear hear, you have presented one of the better explanations as to how
selection guides evolution. The concept of randomness as well as
evolvability have caused much confusion and continue to do so.
What I have found particularly confusing at first was the concept that
neutrality can evolve and is under selective pressure. Imagine that...
neutrality can be selected for. Now that's a fascinating concept which
helps explain many findings in nature. Some even have argued that
neutrality is essential in evolvability.
Received on Sat Oct 1 16:13:20 2005

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