A.C.H. wrote:
> William Morse  wrote in message
news:...
> 

>>I do agree with the general nature of your argument - that there will be 
>>no continuing evolution by natural selection (OK Larry, drift may still 
>>play its part) in the absence of continuing selection pressure.
> 
> 
> The argument i was trying to make was more specific then that. I was
> trying to argue that the selection pressure DECREASES when a
> population gets more adapted.

This will be true if the fitness function is concave near the maximum, 
which I think is what most evolutionary biologists would assume.

> And because natural selection decreases (though it doesn't stop), a
> state of perfect adaptation (ALL individuals survive a certain
> selection pressure) can not be reached.
> 
This will be true if drift and mutation (and immigration) are also 
affecting the population.  The extent to which these are important will 
depend on the sizes of their effects relative to the width of the 
fitness curve.

In practice, deciding if you're right is an empirical exercise, and will 
give different answers for different traits.  many (some?) genes 
involved in respiration are probably optimal, because they are so 
important, and a small change will have a big effect.  Traits like skin 
colour are probably under much milder selection, so more variation is seen.

Bob

-- 
Bob O'Hara

Dept. of Mathematics and Statistics
P.O. Box 68 (Gustaf H„llstr”min katu 2b)
FIN-00014 University of Helsinki
Finland

Telephone: +358-9-191 51479
Mobile: +358 50 599 0540
Fax:  +358-9-191 51400
WWW:  http://www.RNI.Helsinki.FI/~boh/
Journal of Negative Results - EEB: http://www.jnr-eeb.org
---
ţ RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info{at}bbsworld.com

---
 * RIMEGate(tm)V10.2á˙* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 8/31/04 1:13:12 PM