Re: DNA sequence space

From: Jim Armstrong <>
Date: Fri Sep 30 2005 - 02:36:04 EDT

Cornelius Hunter wrote:

> Pim, JimA, Randy and Terry:
> Pim, your wrote:
>>> Actually, the idea that the full design space need not be searched
>>> is weak, and the idea that the search is not random is non
>>> evolutionary.
>> Huh, the search is non random in the sense that selection guides it.
> Ah, need to be careful. Again, NS guides nothing, all it does is kill
> off the bad designs. At any given point, variation must be unguided,
> so it must land on a functional nearby point. There is no such thing
> as "selection pressure," though this metaphor is commonly used. NS
> does not encourage or draw out the variation in any way. In fact,
> every little bit of variation that is supposed to occur over time
> (such as via mutation) must occur on its own. The bat, cheetah and
> human all were created soley by a series of unguided variations. If
> you believe that I have some property in Florida you'll be interested in.

I guess I agree with you somewhat on this point, particularly if "NS
guides" is interpreted to mean that on average the "guidance" moves a
sequence of incremental changes in a particular predetermined direction
and outcome.

But I think NS is mostly understood more as a negative space influence,
determining what is not successful, and in doing so leaving viable that
which is. So it perhaps bounds, but doesn't lead. But it nevertheless in
doing so has an influence on direction.

> JimA, you wrote:
>>> So random, unguided biological changes must find and then follow
>>> these pathways. NS does not help these random changes to occur.
>> No, it causes them.
>> Or so it seemeth to me. JimA
> This is the myth of "selection pressure."

When I trim my bougainvillea into espallier form, flat against our brick
wall, I do so by trimming off everything that isn't in the desired
two-dimensional plane.
Notably, I have not guided the surviving branches. I have only clipped
off the undesirable ones.
But in doing so, I have certainly influenced the resultant plant shape
into a planar form. Is that (negative space) selection pressure
(obviously not of the heritable kind)?

Regards - JimA
Received on Fri Sep 30 02:55:46 2005

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