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EQDOMAIN.EQWQ.LROGERS at EMAIL.STATE.UT.US EQDOMAIN.EQWQ.LROGERS at EMAIL.STATE.UT.US
Thu Jun 29 08:17:26 MDT 1995


with Novell_GroupWise; Wed, 28 Jun 1995 22:08:13 -0600
Message-Id: <sff1d2cd.085 at EMAIL.STATE.UT.US>
X-Mailer: Novell GroupWise 4.1
Date: Wed, 28 Jun 1995 22:08:31 -0600
From: Lisa Rogers <EQDOMAIN.EQWQ.LROGERS at EMAIL.STATE.UT.US>
To: marxism at jefferson.village.virginia.edu
Subject:  evolution, basics to advanced plus some 'evolutionary

    economics' at the end.

Hi to you too, Ron.  Here I address a few of the issues you brought
up.  Thanks for asking.

"Evolution" without any baggage just means change, or pre-Darwin in
bio it meant change in physical form of living things, over rather
long time spans, including geological time (consider that during
17+1800's the bones of giant, extinct but recognizable bear, ox and
such were turning up in gravel pits in Europe, so the fact that there
had been change was obvious, but the mechanism was not).

Today, in bio, it means "change as a result of Darwinian natural
selection."  (This includes change in gene frequencies, which is the
proportion of genes at one location on a chromosome which take
various forms; blood group genes for example.  Everybody has two
genes for blood type, AO, AA, OO, BO, BB or AB.  Count 'em all up,
let's use this pop. of 6 for an example, and you can get a proportion
in the form of a decimal fraction, i.e. the freq. of the A gene in
this population is 4/12=.33  Then evolution can be seen as a change
in this number between generations.  There are other ways to look at
it too, but this micro-view is always presumed to be working,
although it is often invisible.)

Lamarck is about one individual acquiring physical changes during its
own lifetime, and as a result being able to pass these to its
offspring immediately.

Darwin says there is heritable stuff that has variations between
individuals from birth.  This stuff does not change during life
[stuff we now know as DNA and genes, think of the blood groups, these
do not change during one's life].  The only way that the next
generation will be different from this one is that some of those
variations present now are not going to make it, genetic variations
may not all live to reproduce at the same rates.  "It is as if Nature
herself selects which ones will live or die or have more offspring."
(paraphrase of Darwin in Origin of Species, hence Darwin's
metaphorical phrase "NS")

In other words, natural selection is differential reproduction which
is related to genetic variation.

Otherwise, differential reproduction alone leads to no genetic
changes in the population, when those who live and those who die have
the same genes on average.

"Adaptation" is a result of NS, in terms of each generation becoming
more closely matched to the demands of the local, relevant
circumstances.

There has been a lot of talk about people getting taller and it is
true, in a way.  It has everything to do with food, large quantities,
from an early age, which also includes physical work loads, as more
work has similar effects to less food (it's a lot about calorie
balances).

So, over the last 200 years, yes, europeans and euro-americans have
gotten significantly taller.  Work was also done on Japanese-and
Chinese americans, with the generations bridging the immigration.  An
even bigger difference in heights is observed, over only three or
four generations.  The family photos are very striking - line
relatives up by age and you get stairsteps.

In the euro-us data, it is also striking that the age at menarche
(girls' first blood) has dropped a lot, from about 17 to 13, at the
very same time.  (I expect the same for other populations, but I have
not seen data.)

(In anthropology and medical-anthro there is a large body of on-going
work concerning fertility, fat stores, ovulation, growth rates, birth
rates, caloric balance and so on.)

None of these changes over time are "evolution" in the Darwinian
sense, because none of them involve any genetic change in the
population as a result of some variations being weeded out.  These
changes are examples of the same genes being able to respond
differently to different circumstances.

This is also not a random response, or an obvious and inevitable
response.  The question of how development will proceed in various
circumstances, is itself related to evolutionary history.  It is not
only the case that genes and environment interact, but genes are
designed [if I may speak metaphorically] to interact in specific
ways, such as "get bigger when possible, but only up to some point."

It is not only the case that more food makes bigger possible, but it
must also be useful (evol. advantageous) to be bigger under many
circumstances, or else this particular response of development to
environment would not itself have evolved and survived until now.

This may be a good place to introduce the evol.biol. concept of
resource allocation and the evolution of life histories [schedules of
growth, reprod. and death].  Each living thing has available for its
use only a certain amount of resources, mainly structural nutrients
[chemical building blocks], energy [calories] and time [lifespan,
daylight, this season, etc.]

The amounts of these things are not just given, there are tradeoffs
among them.  For instance, one might be able to choose between foods
with more useful chemicals in them, such as animal bodies which
contain amino acids and fatty acids, so that the consumer need not
manufacture these things from scratch, or one could eat plants.  Yes,
in the short run, one may be locked into one way by present body
structure and physiology, but in the long-enough run, everything is
evolutionarily changeable, and complexes of traits are separable.

When one is in a given situation, and given the contraint that one
can tolerate negative calorie balance for only so long before death
intervenes, what is one to do?  Pursue high returns at low cost, of
course.  More calories for less time, especially when there are other
things to be done with "extra" time, including avoiding predators.

Well, given my discussion of NS above, it should be clear that
survival is necessary but it's not everything.  We're dealing with
living things that have all been produced by NS, so what should we
expect?  Behaviors of living things [including plants] are oriented
towards survival and reproduction.  How much reproduction?  As much
as possible.

Enough is never enough reproduction when evolution is the name of the
game.

(This is why birds do not restrain their clutch sizes for the
"benefit of the species" or the local group.  Each robin 'restrains'
herself to only 4 eggs because if she laid more it would reduce each
offspring's chance of survival more than the extra eggs would be
worth to her.  She and her mate have only so much time in the day and
are further constrained by the local food supply and weather, so they
can only bring so much food home, and if all the offspring share and
so all are hungry and small, none may make it to the next year to
breed at all!)

So, resources are limited, but needs are unlimited.  Any additional
resources may usually be turned into more survival or more
descendants.  Then the question is by what means?  To grow larger
before reproducing may mean more eggs per season later on, but the
longer one waits before starting to reproduce, the likelier it is
that one will not survive that wait.  To hide from predators will
increase chance of survival, but one may miss opportunities to spread
sperm.  Seek more mates or guard this one or feed kids, etc. etc.
Everything is a tradeoff.  Not all things can be simultaneously done
very well, because investing more in one thing means one must do less
of something else.

If the circumstances [environment, including social env. for some
critters] are matched better, more successfully [in terms of number
of descendants] by some variations in resource allocation rather than
others, [and if there is some corresponding genetic variation] that
is NS.  From all the various circumstances of the last 4 billion
years or so, NS has resulted in a great diversity of lifeforms
indeed, from desert flowers with lifespan of 6-8 weeks to pines that
may live a century before even producing any pollen.

Doesn't this sound like some economic problems?

Enough for now,
Lisa






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