From: Scott Chase (ecphoric@hotmail.com)
Date: Tue 17 Feb 2004 - 23:31:21 GMT
>From: "Dace" <edace@earthlink.net>
>Reply-To: memetics@mmu.ac.uk
>To: <memetics@mmu.ac.uk>
>Subject: Re: memetics-digest V1 #1480
>Date: Tue, 17 Feb 2004 13:59:44 -0800
>
> > From: Keith Henson <hkhenson@rogers.com>
> > Subject: Re: the meme/brain problem
> >
> > > > Evolution does not happen to organisms. They live or die, reproduce
>or
> > > > fail.
> > >
> > >An organism is not just a sack of molecules. What evolves is the form
>of
> > >organisms rather than their material constituents.
> >
> > When you are talking about Darwin and evolution, *species* are the level
> > subject to evolution. *An* organism (individual) is stuck with the form
>it
> > has.
>
>An organism is a living form that's stuck with a particular set of
>molecules
>(though, over time, it undergoes a complete changeover of molecular
>constituents). An individual is a materialization of a collective form.
>What evolves is not the materializations but the form. However, as Darwin
>emphasized, evolution is propelled forward by adaptations made by
>individual
>organisms. Though Darwin had no idea how such inheritance occurs, he
>maintained to the end that without this ability to pass on acquired
>characters, evolution as a theory is dead on the water. For Darwin, the
>organism is the central actor in natural evolution, and I would add that
>the
>same is true of the person in cultural evolution.
>
Individual organisms are the level at which selection operates, but
populations are the level at which evolution occurs. The quick and dirty
definition of evolution is ("not again!" they scream from the peanut
gallery) 'changes in allelic frequencies within a population over time'.
Thus (is this where I insert a Q.E.D.?) evolution requires a group of
organisms or *population* and a time period, which can be taken as
subsequent generations. Flail around as you will, you are wrong on two
counts if you assert evolution happens to individuals. Not only are you
ignoring populationns, you are ignoring the generational aspect of
evolution.
Individuals can change (or adjust) during a lifetime to match the needs
imposed by the environment within a reaction norm influenced by their given
genetic repertoire, but they are not evolving. Their success at surviving
and reproducing may impact the allelic frequencies of their population, but
this is a shift in focus, from selection operating upon an individual to the
change in proportions of individuals with given traits in a population over
generational time.
And given the definition of evolution above, if the population size is small
enough, alleles can fluctuate in frequency due to nothing more than sampling
errors. A selectively advantageous allele could become lost to a population
because of chance or a selectively detrimental allele fixed likewise. This
is genetic drift which gives another good reason not to equate selection
with evolution (evolution occurring in populations where selection operates
upon individuals being another good reason not to conflate evolution and
selection).
Understood?
Since a species is a group of populations, Keith is way more on target than
you are. The definition of evolution in the Glossary of Futuyma's
_Evolutionary Biology_ (3rd edition) mentions changing populational
proportions within a species as a subdefinition.
So there.
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