from Gary Cziko 970221.0330 GMT]
I appreciate the feedback and discussion from Bill, two Bruces, Tracy and
Rick (did I miss someone?) on my comment about evolution.
It is interesting that a very similar discussion occurred in Darwin's time.
The term "natural selection" itself evolved from Darwin's own thinking.
He saw how domesticated animals and plants evolved over time because of the
selection of farmers. But he had a very difficult time figuring out why
evolutionary changes took place in nature without meddling humans.
Then Darwin read Malthus's discussion of how populations of organisms tend
to increase geometrically, much faster than the growth of resouces, and it
occurred to Darwin that this would result in a type of "natural selection"
that did not require human involvement. It is interesting that Alfred
Russel Wallace's independent discovery of "natural selection" was also due
to reading Malthus's work.
But Wallace did not like the term "natural selection" at all, for reasons
very much like those of Bill Powers. He was afraid that it would lead
readers to believe that some purposeful supernatural agent was involved in
the selection. So Wallace preferred Herbert Spencer's term "survival of
the fittest." But Darwin stuck with "natural selection" because of the
role the analogy with domesticated animal played in his own thinking and
his argument in the _Origin_.
Leaving history and daring to stick my neck out some more, I would like to
propose that four types of selection can be involved in evolution.
Level 1 Selection: Nonpurposeful "selection" due to inanimate environmental
factors such as climate change. This is the "natural filtering" that Rick
described in which there is "just passive filtering -- survival of those
happen to make it through the "holes" in the environmental sieve." As the
climate gets colder, those bears with thicker coats will make it and those
with shorter hair will not.
Level 2 Selection: Selection due to the incidential _side effects_ of other
purposeful organisms. Tall giraffes make it because they can reach food.
Shorter giraffes will not (because the taller ones have already eaten all
the food it could have reached). Frogs become extinct because of humans
draining of wetlands and industrial pollution while blue-green algae take
over polluted waterways.
Level 3 Selection: Selection due to one organism's direct interaction with
another. Slower gazelles don't make it past the cheetah but faster ones
do. Peacocks with less showy tails find no mates but better endowed
peacock's do. For early agricultural humans, plants which held their grain
until maturity (called "non-shattering" by agricultural scientists) made it
since the early farmers could more easily gather this grain and use it to
plant more crops. I like the human example here since it shows that humans
may select plants and animals for reasons unrelated to their continued
evolution but influence their evolution nonetheless. At this level
evolution is a incidental side effect of one organism's control of
variables involving another organism.
Level 4 Selection: Selection of organism A by organism B when organism B is
controlling for the evolution of organism A. This is what modern human
plant and animal breeders do today.
Before the arrival of sophisticated humans who understood how evolution
works, only Levels 1 through 3 existed. Can anyone imagine or give an
example of how only Level 1 or 1 plus 2 would be factors in the evolution
of a species? Perhaps asexual, nonsocial organisms who have been
introduced to a new niche where there is (for a while) unlimited resources
Note that whether or not others like my four levels of selection, thinking
of evolution in this way and this entire interesting discussion would be
impossible without HPCT.