From: colby@bu-bio.bu.edu (Chris Colby)
Newsgroups: talk.origins
Subject: evidence for cumulative selection
Date: 28 Jan 93 22:30:52 GMT
Organization: animal -- coelomate -- deuterostome

In article <1k8u78$nu1@agate.berkeley.edu> philjohn@garnet.berkeley.edu (Phillip Johnson) writes:

>That natural selection is not a "creative process" is exactly my
>point. 

Do you mean natural selection by itself or cumulative natural
selection (iterated episodes of mutation and selection)?

>That is why it does not explain the fantastic growth in
>the complexity of the genetic program needed to govern the
>biological processes of plants and animals.

Out of curiousity, how much do you know about genetic programs 
and biological processes? If you are confident to state that
selection does not explain them, you must know a whole lot, huh?
What is your training in biology, Mr. Johnson? Why should we believe
your assertion that selection isn't enough when people who have 
studied biology all their lives have said it is? (Hint: try producing
some evidence. You're a lawyer, you must know what evidence is.)

>If the peppered moth
>example is "by definition, evolution," then evolution is not a
>very important subject.

Bullshit, many scientists and grad students study evolution as
it is happening now and it is a very fascinating subject. Not
only is it interesting scientifically, but it also has numerous
practical implications. Agricultural companies are very interested
in how crop pests develop restistance to pesticides. Likewise,
ways to breed for better quality animals and plants, obviously,
is of interest to some. In a different vein, conservation biologists
and zookeepers benefit from knowledge gained in evolutionary studies
as they can better plan to maintain genetic variation in endangered
species. The project I just finished up was partly funded by the
American Cancer Society. Is cancer not a very important subject,
Mr. Johnson?

>The important question is how relatively
>simple forms like bacteria become far more complex forms like
>plants and animals.

I agree that this is an important question.

>If the peppered moth example explains this
>also "by definition," then what you call evolutionary science is
>nothing more impressive than the manipulation of definitions.

Did I say the peppered moth example explained this? Hint: was the
point of my recent selection post perhaps explicitly that
natural selection _by itself_ couldn't explain it? To explain
this one needs to invoke cumulative selection.

>BTW, I was teaching a seminar yesterday, with a critique of the TV
>version of The Blind Watchmaker.  All about the vast *creative*
>power of natural selection, quite a contrast with the Colby
>doctrine.

Perhaps if I drew you a picture. Dawkins is talking about cumulative
selection; e.g. numerous repeated cycles of mutation and
selection. I was talking about natural selection (one of the
components of cumulative selection).

>And yes, I know all about cumulative selection. 

Why then, in _DoT_, did your discussion of cumulative selection
focus only on natural selection?

Evidence for cumulative selection comes from two sources: direct
observation of its components and inferences from patterns seen
in biological systems. Biologists such as Dawkins have claimed
that complex adaptations are the result of cumulative natural
selection. What is their evidence? Well, cumulative natural
selection has two components 1.) mechanisms to introduce genetic
variants -- usually mutation and 2.) a mechanism to amplify some of
the genetic variants introduced by 1 -- i.e. natural selection.
So, biologists have documented each of these components individually.

Numerous studies deal with mutation (from medical studies, to
molecular biology experiments to evolutionary biology). And likewise,
there have been numerous demonstrations of natural selection altering
the frequency of genetic variants in gene pool where genetic variation
already existed. Studies showing combinations of these are limited
at this time. P elements were introduced by gene flow into _melano-
gaster_ in the 1940s and quickly spread through the world-wide
population. A duplication of a pesticide resistance gene spread
throughout the worldwide mosquitoe (species _Culex pipiens_)
population. I am not aware of any studies that show multiple
"turns of the crank".

So, does this mean evolutionary biologists must wait millions of years
before we can witness firsthand and thus say anything about cumulative 
selection?

No. Biologists, like all other scientists, can make inferences from
other sets of data. For example, if cumulative selection was responsible
for creating complex traits, we should see evidence that organisms are
modified by descent. The "mutation-selection-mutation-selection..."
model predicts that features of organisms should show evidence of
being modified from features of their ancestors. This is born out
by examining developmental biology and by simply studying traits
of organisms and seeing if they appear to be "jury-rigged" (and by
looking at closely related species to get an idea of what they 
might have been jury-rigged from.) You're a lawyer, Mr. Johnson,
you must know what jury-rigging is 8-)

Also, if traits are modified with descent, and lineages of
organisms bifurcate into separate lineages (speciate), a nested pattern
of biological traits should be witnessed amongst living organisms. 
This is what we see in the world today. In fact, this was seen
long before the theory of evolution existed. This nested pattern
of traits is the basis of taxonomy.

So, evolutionary biologists have documented the independent components
of cumulative selection and shown that the pattern of biological
traits observed in living species matches the prediction of the
theory. Which of these topics would you next like to discuss,
Mr. Johnson?

>You seem determined to obscure the issues
>in word games.  No wonder.

I don't consider carefully defining my terms word games.

>Phillip E. Johnson
>  School of Law, University of California, Berkeley CA 94720

Chris Colby 	---	 email: colby@bu-bio.bu.edu	---
"'My boy,' he said, 'you are descended from a long line of determined,
resourceful, microscopic tadpoles--champions every one.'"
 	--Kurt Vonnegut from "Galapagos"