From: BillK (bill@wkidston.freeserve.co.uk)
Date: Tue Aug 05 2003 - 07:29:12 MDT
On Mon Aug 04, 2003 07:11 pm Lee Corbin demanded:
>
> Yeah, what is it about this aspect of evolutionary theory
> (that evolution tautologically causes the predominance of
> those who reproduce most) that is so hard for many to
> internalize? As you and I keep saying, it only takes one.
>
OK, I think I can have a go at this one.
Basically, your tautological thesis is simply not true.
i.e. it is not what happens in the world as we know it.
First, a primer on the two population types:-
There are two basic strategies for populations, r-Strategists and
K-Strategists.
r-strategists
The r-strategists approach to continued survival is through rapid
reproduction, i.e., a high value of r. In fact, if we consider an
organism a pest, it is probably an r-strategist.
In general r-strategists share a number of features:
1. They are usually found in disturbed and/or transitory habitats.
2. They have short life spans. The house mouse, with a maximum life span
of 3 years, is an r-strategist.
3. They begin breeding early in life.
4. They usually have short generation times; that is, they have short
gestation periods and are soon ready to produce another crop of young.
The housefly can produce 7 generations each year (each of about 120 young).
5. They produce large numbers of offspring. The American oyster,
releasing a million eggs in one season, is an r-strategist. Most of its
offspring will die, but the sheer size of its output increases the
likelihood that some offspring will disperse to new habitats.
6. They take little care of their offspring, and infant mortality is
huge. Although humans are not r-strategists, the higher reproductive
rate in countries like India may well be a response to the higher rates
of infant mortality.
7. They have efficient means of dispersal to new habitats.
For r-strategists, alleles that enhance any of the traits listed above
will be favored by natural selection.
K-strategists
When a habitat becomes filled with a diverse collection of creatures
competing with one another for the necessities of life, the advantage
shifts to K-strategists. K-strategists have stable populations that are
close to K (the maximum population an environment can support). There is
nothing to be gained from a high r. The species will benefit most by a
close adaptation to the conditions of its environment.
Typically, K-strategists share these qualities:
1. They are usually found in stable habitats. Most of the species in a
mature forest will be K-strategists.
2. They have long life spans. The elephant and the tortoise are
K-strategists.
3. They begin breeding later in life.
4. They usually have long generation times. It takes 9 months to produce
a human baby.
5. Most produce small numbers of offspring. Birds are K-strategists,
most species producing fewer than a dozen young each year.
6. They take good care of their young. Infant mortality tends to be low.
7. K-strategists typically have evolved in such a way that they become
increasingly efficient at exploiting an ever-narrower slice of their
environment. Thus it is not surprising that many endangered species are
K-strategists.
For K-strategists, alleles that enhance their ability to exploit the
resources of their habitat; that is, to increase the carrying capacity,
K, of their environment, will be favored by natural selection.
Right, read all that? Pay attention at the back!
It seems probable to me that an advanced civilization will be a
K-strategy, monoculture population with no need or desire for rapid
reproduction. (They may send out probes for curiosity's sake, but no
expansion).
However, Lee may well claim that all bets are off and an advanced
civilization can have whatever reproduction rate that Lee likes. What
Lee wants is an r-strategy reproduction rate linked to an advanced
K-strategy civilization. Very unlikely, in my opinion.
So, here is a more general discussion on why K-strategy advanced
civilizations will not do rapid expansion.
If everything was perfect for a population and all the individuals in
the population survived and reproduced at the maximum rate, that growth
rate is called the biotic potential. For example, when fish are
introduced into a lake where there is plenty of food and space and there
are no predators, the fish can reproduce at their biotic potential, but
not for a long time. This is exponential growth, until a limit is
reached. This is the perfect growth case that Lee believes will apply to
at least one advanced civilization which will take over the universe and
seed it with millions of Lee impressionists.
(I'm the real Lee! - No, I am ..... No, It's me really ........:)
The possible limiting factors to population growth are many and
exponential growth must successfully defeat every one of them.
Note 1: Perfect reproduction assumes perfection all the way down.
Here are some of the possible limiting factors to population growth:
(Not all of which will necessarily apply to a post-singularity civilization)
Birth Rate. Assuming advanced civilizations have complete control of
reproduction, then choice is the limiting factor here.
How many factories do we want to build, churning out mini-Lees?
Why would I allow him to do this, when mini-Bills are obviously much to
be preferred? ;)
You must also assume that mini-Lees are instantly self-supporting or
your time and resources will be spent supporting them (and limiting your
reproduction to what you can support).
Why reproduce if the existing population is not dying?
How will it benefit the existing population? (rather than being a drain
on resources).
Spreading the population around as security against disasters could be
thought of as a benefit. But an immortal civilization with total control
of the environment probably deals with any problems as a triviality.
Try to think of reasons that might appeal to a very advanced immortal
civilization (rather than just procreating to spread my genes around).
Unlimited resources or life energy. A given supply of food and water
might be enough for a small population density. However, that same
supply might not be enough for a high-density population, and
competition among the individuals of the population would develop.
Competition is a force for evolution to occur. An advanced civilization
will only evolve by choice.
Note 2: Unlimited resources means no competition, no competition means
no natural evolution.
Note 3: Unlimited reproduction will eat the universe.
Stress. Many species need lots of territory to breed, like the mountain
lion. If there is no room, an organism can become stressed and have
lower birth rates.
Note 4: Unlimited reproduction means unlimited expansion and physical
movement between stars.
Pollution. Population affects the environment. So you have to devote
time and energy to cleaning up the mess.
“Population growth is the primary source of environmental damage.”–
Jacques Cousteau.
Space. This is an obvious limiting factor, especially if you think of
fish in a lake. If you assume the universe is unlimited, then you can
keep on expanding, eating as you go. Although as the universe seems to
be expanding faster and faster, there may be a limit to what you can reach.
Predators. Higher densities of a prey population attract more predators
and as the number of prey increases, so does the number of predators. On
the other hand, if the number of prey decreases, so does the number of
predators. Unlimited growth assumes that you won't meet any predators.
Are the Blue Meanies waiting to pounce?
Other exponential growth populations. You might meet aliens coming the
other way as you expand. If you meet yourself, then you've proved that
it is a closed universe. ;)
Diseases. Diseases can certainly have an impact on birth rate and thus
affect growth rate. Since many diseases are contagious, they are
therefore dependent on density. This could include mental infections
which could cause population restrictions.
Parasitism. Parasitism is a relationship where one organism (the
parasite) feeds on the tissues or body fluids of another organism (the
host). In this type of relationship the parasite benefits and the host
is harmed, sometimes to the point of killing the host. Like diseases,
since parasites spread easier in a high-density host, their impact
depends on the density.
The Universe. Natural disasters, meteor strikes, novae, black holes -
It's dangerous out there!
Ooooh! To frightening for me. I'm going back to my rocking chair now :)
BillK
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