Re: An introduction

forcythe@xxxxxxx wrote:

In article <lWFRf.43572$2O6.16427@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
John Harshman <jharshman.diespamdie@xxxxxxxxxxx> wrote:


forcythe@xxxxxxx wrote:


In article <wLBRf.38567$_S7.36212@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
John Harshman <jharshman.diespamdie@xxxxxxxxxxx> wrote:



forcythe@xxxxxxx wrote:



In article <JbnRf.56362$Jd.7221@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
John Harshman <jharshman.diespamdie@xxxxxxxxxxx> wrote:




forcythe@xxxxxxx wrote:




Scientifically why is evolutionary theory treated almost exclusively as
Darwinism or Neo-Darwinism and its unyielding focus on natural
selection and an oversimplified concept of mutation via genetic
mutation? Both sides of the debate are often guilty of this error, and
it makes the whole discussion pretty useless.

Agreed for the first part. But it only makes a part of the discussion
useless.




Clearly natural
selection is very important as the "bottom line" so to speak,
determining in the end the differential advancement of existing
variation, but it speaks little to the source of variation.

Of course. It speaks nothing to the source of variation, which is
mutation.

Genetic mutation is the "raw source" of variation, but alone is not a
strong enough force to explain the variation required for the evolution
we observe. Means for that genetic variation to spread and affect the
variety of phenotypic variation it may cause within populations is
necessary, and itself is a stronger force of evolution than mutation.
Here I'm thinking primarily of drift (and to a lesser extent
migration), too often ignored and necessary for the model to stand.

I don't actually think that drift is necessary to produce much of the
interesting (in an adaptive sense) variation we observe. It obviously
has big effects on the total variation. But in the complete absence of
drift we would still see most of the same diversity of phenotypes
between species, and most of the adaptive evolution. Drift is clearly an
important player, though, since most variation is neutral. There may be
some confusion about what "source of variation" means.

I'm happy I've got at least one point on which to respond to you here
unsullied by my more egregious slips in terminology. Unfortunately
there doesn't seem to be much to grab on to here except to say I'm not
sure I agree.

My understanding of evolution has a heavy component of population
genetics, and my understanding of population genetics has drift as a
major player in shaping the variability of a population to give
selection something to act upon. As a quick example (these seems to
get me in trouble), it's for this reason that I don't expect to see any
major movement in human evolution as long as we've got this global
population of 6 billion with few if any small isolated groups.
Furthermore, it accounts for much of my understanding of existing human
variability established previous to the rise of globalism. Without
such a population component, I don't understand how mutation alone
could have its necessary effect.

I think this is still confused. Drift has the effect of maintaining
variability in a population, but it also has the effect of reducing
variability. In a growing population, variability will increase, so if
drift making variation available to selection is your point, that will
only increase with population size. The bigger the population, the more
mutations happen for selection to seize on. Evolution does not go faster
in small populations, though a few effects (nearly neutral evolution;
breakup of hypothetical "coadapted gene complexes") are stronger in
small or bottlenecked populations. But in general, you don't need small,
isolated groups.

Variability is decreased within a population, but is increased between
sub-populations undergoing the same process.

So you're going for a sort of Sewall Wright shifting balance sort of
argument? If we're talking about neutral evolution only, a single large
population will contain as much variation as a set of smaller
populations that sum to the same total. And if you are thinking of
random variation and recombination as the raw material for selection,
that single large population will have the possibility for more genotype
combinations than will the whole set of small populations. You are going
to have to add some variation in selective regimes to the mix if you
want to get anywhere with this. Or perhaps an attempt to cross an
adaptive valley. Or go with nearly neutral, not strictly neutral, evolution.

[snip]

.

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