Text 882, 75 rader
Skriven 2004-11-25 16:26:00 av William Morse (1:278/230)
Ärende: Re: The "fuel" of evoluti
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"EKurtz" <NoJunk@ForgetIt.com> wrote in
news:co3a8t$1i2h$1@darwin.ediacara.org: 

> "phillip smith" <deletethis-phills@ihug.co.nz> wrote >
> 
> How can we know this. Presumably we can only know this when the
> individual 
>> is dead. As they may other wise have more offspring in the future.
>> Also do you count the fertile offspring if they all fail to reproduce
>> even if though
>> are fertile. They may be fertile but have a mutated mate recognition 
>> system
>> or perhaps they breed  but the next generation dies.
>> Mutations like grandchild less
>>
>> http://www.ucalgary.ca/UofC/eduweb/virtualembryo/mago.html
>>
>> Would up set your case. If you parents produced offspring with the
>> grandchildless phenotype would be fertile but would have no
>> grandchildren 
> 
> Looking at this issue from the point of view of an outsider, I get the
> feeling that "fitness", which is essentially a statement about
> probability of survival (of something) over time, has been reified
> into an attribute of an organism, similar to objective characteristics
> such as weight and color. As a result, we are eternally immersed in
> pointless theological disputes about its meaning and relevance.
> Consider the case of a sexual species into which a parthenogenic
> female is introduced by mutation. Assuming that she and her immediate
> offspring survive, and that the population size is constant, her
> offspring will effectively displace the sexual type in a few dozen
> generations. But ultimately the population will likely succumb to
> disease as a result of lack of genetic diversity. So what is the
> "fitness" of the mutation that caused the transformation?  A
> meaningless question, in my view. The only thing that matters is the
> probability at any time after the mutation is introduced that its
> populational frequency has a given value. Without the introduction of 
> time and probability, no understanding of fitness is possible.
> When we say that a novel variation confers "fitness", we are merely
> guessing about its effect on the population in the near future.
 

This has been much discussed, but I will jump in again. I can agree that 
fitness is a statement about probability of survival, but that 
probability _is determined by_ objective attributes of an organism. To 
grossly oversimplify a complex subject, in a number of niches organisms 
that can fly will survive better than those that can't, unless they 
happen to wind up on an island with no significant predators. Organisms 
with long pointed snouts, strong claws, and no teeth will be better at 
eating ants than those with different characteristics. Organisms that can 
see will survive better than those that can't, unless they happen to live 
in caves. 

Now probability is definitely important, as witness the significance of 
drift in evolution. And fitness is always relative to the environment, 
which changes with time. So I also agree that any statement about the 
"fitness" of a novel variation can only be a probabilistic assessment. 
But let us not throw out the baby with the bathwater. We can in fact make 
assessments about probable futures (e.g. via Markov chains), so if we can 
come up with a realistic estimate of the added fitness of a given 
variation (the devil as usual is in the details), we can make meaningful 
predictions.

Yours,

Bill  Morse
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