lamoran{at}bioinfo.med.utoronto.ca (Larry Moran) wrote in
news:c9b74h$vr$1{at}darwin.ediacara.org: 

> On Thu, 27 May 2004 16:40:40 +0000 (UTC), 
> William Morse  wrote:
>> lamoran{at}bioinfo.med.utoronto.ca (Larry Moran) wrote in
>> news:c92cvu$3te$1{at}darwin.ediacara.org: 
>> 
>>> On Tue, 25 May 2004 23:48:32 +0000 (UTC), 
>>> William Morse  wrote:
>> 
>> (snip)
 
>> The same wise man also suggested the following definition:
 
>> "Evolution is a process that results in heritable changes in a
>> population spread over many generations."
 
> This must have been a very wise man. By saying "heritable changes" you
> avoid semantic quibbles over the definition of an allele.
 
>> (And just in case you get any ideas, if you start quoting things I
>> have previously said back at me I'll come and stuff your hard drive
>> full of peanut butter. Toronto ain't all that far from Syracuse :-)
 
> Don't worry ... I haven't paid much attention to anything you've said
> in the past.   :-)

Touche!
 
> Let's no quibble. The minimal definition of evolution is a change in
> the heritable characteristics of a population over time. Changes in
> junk DNA count as evolution by this definition whether you want to
> call them alleles or not. They my not be very interesting changes to
> most people who aren't interested in genomes but that doesn't mean
> they don't exist. 
> 
> Would you prefer a definition where evolution is confined to changes
> in genes (alleles by your definition)? Do you realize what this would
> mean? 

See my comments below.



>> Now I can't define evolution only as changes in functions of genes
>> unless I can define genes, and I don't really want to try to do that.
>> Furthermore, a change in a regulatory sequence would certainly also
>> qualify as evolution in my book. However I do not see a substitution
>> of alanine for glycine in a region far from the active site of an
>> enzyme as necessarily contributing anything to  evolution. So let's
>> try this: 
>> 
>>          Evolution is a heritable, statistically significant change
>>          in a     
>>      population of organisms that  can be detected without using
>>      either     DNA or protein sequence data.
 
> I'm not going to argue with you over new definitions. If you can
> convince the scientific community to accept this then I'll bow to the
> consensus. Good luck.

In order to convince the community I have to start somewhere, and this 
newsgroup is it. But actually I think that your definition - "heritable 
change" -  is the same as my definition. Let's imagine a world in which 
the only change is in "junk" DNA, with no other change that "can be 
detected without using either DNA or protein sequence data". So I have a 
world in which fossil robins look exactly like modern day robins. There 
are no australopithecines, because humans show no discernible change in 
morphology no matter how far back you go in the fossil record. The 
dinosaurs may have existed and been wiped out, but they did not give rise 
to modern birds, because _there is no change other than in sequences_. 
There are lots of changes in DNA sequences, but no changes that can be 
seen by any other method. Morphologies are identical, resistance to 
disease is identical, blood types are identical. 

Now along come two scientists - let's call them Morwin and Wallant -  
with a new theory of evolution, which they explain on the basis of 
changes in sequences of "DNA" which randomly occur through "neutral 
drift" but which create absolutely no other change which anyone can 
measure by any other technique. Scientists solemnly note that independent 
research supports this theory - but  go on to say  that the result is 
interesting but of no theoretical value. The population as a whole quite 
rightly ignores the new theory and goes on to other pursuits, because 
this "evolution" _does not change anything_. 


(snip) 
 
 
>> I had a rant about this subject recently, and it seems to be rearing
>> its ugly head again. Are you including sampling error as part of
>> drift, or defining drift as just neutral mutations? My statement on
>> population size dependence only applies to sampling error - which is
>> in fact exactly what I said ;-) The population genetics equation for
>> this type of drift is: 
 
>>  delta q = pq/2N
  

> This is true for a particular individual allele. If it occurs in a
> large population it will likely be eliminated. If it occurs in a small
> population it has a better chance of being fixed.

> However, when you look at the overall rate of evolution by random
> genetic drift you have to take into account two things: the probabilty
> of fixation, and the rate of mutation. There are more mutations in a
> large population and this exactly balances the decrease in the
> probabilty of fixation. Thus, the rate of fixation of new alleles in a
> diploid population is .... 
 
>       K = 2Nu (1/2N) = u
 
> where u (mu) is the rate of mutation. The overall rate of evolution by
> random genetic drift is independant of population size.

No, this is only true for neutral mutations, and truly neutral mutations 
do not cause evolution, at least until enough of them accumulate so that 
they are no longer neutral - unless you still maintain that a change that 
doesn't change anything is a change. Deleterious mutations will rapidly 
be eliminated in large populations, and severely deleterious mutations 
will rapidly be eliminated in all populations. A dominant lethal mutation 
has exactly zero chance of being fixed. Advantageous mutations will 
rapidly (in evolutionary terms) be fixed, at least if they survive 
sampling error while still at low frequency.  


 

>> Apparently you are accusing adaptationists of being niche-pickers :-)
> 
> I like that ... can I use it?

Since you did not object to being called a drifter, how can I refuse?
 
>> But I am going to put this back on you. Since in fact sampling error
>> is dependent on population size, which is determined by the niche,
>> all of this form of evolution is dependent on niches. 
> 
> The rate of evolution by random genetic drift (sampling error) is
> independent of population size.

No, only the rate of _neutral change_ in DNA is independent of population 
size. The rate of _evolution_  (non-neutral change) by sampling error (if 
we are  calling that drift) is dependent on population size.  

 
> Thanks for playing. There are no consolation prizes for niche-pickers.
>   :-) 

You are right - there are only first prizes :-)


 
>> I would like to spend more time on the subject of niches, but this is
>> getting long and that subject might be better treated in a new
>> thread. 
 
> You mean we have to find a new niche?
 

No, we're talking about a whole new trophic level here.


Yours,

Bill Morse
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