From: colby@bu-bio.bu.edu (Chris Colby)
Newsgroups: talk.origins
Subject: Dawkins and creative selection
Date: 28 Jan 93 00:33:43 GMT
Organization: animal -- coelomate -- deuterostome

In article <2B64398B.25486@ics.uci.edu> bvickers@ics.uci.edu (Brett J. Vickers) writes:

>You cite Dawkins but give no indication that you have bothered to read
>(or to comprehend) what he wrote.  Dawkins clearly explains that
>natural selection is a creative force; 

I am reasonably certain Johnson's response to me (if he does indeed
respond) will be to ignore the substance of what I said and quote
back some Dawkins' (or other biologist) quotes talking about the
creative power of selection. I have been maintaining that natural
selection is not a creative mechanism. Natural selection is
differential repoductive success of genetic variants -- it only
changes the frequency of _existing_ alleles in the gene pool.

Genetic variation is supplied primarily by mutation, although 
gene flow and recombination are also sources(*). Every new trait
that gives an organism a fitness advantage over its conspecifics
(members of its own species) is introduced by mutation; selection 
only amplifies its frequency in the gene pool. (It wouldn't hurt
for me to mention that selection usually eliminates less fit variants.
A mutation giving rise to a more fit allele is very infrequent relative
to deleterious mutations.)

(*) for the sake of brevity, I'll simply ignore them for the rest
of this post 

So why does Dawkins call selection creative? Because Dawkins is
(quite explicitly) talking about _cumulative_ selection. The main
thesis of "Blind Watchmaker" is that numerous small improvements
made by selection add up to complex adaptations. When Dawkins
speaks of cumulative selection, he is implying that some mechanism
is adding genetic variants to the gene pool. Natural selection
depletes genetic variation; in order for there to be _cumulative_
selection there must be mutation. Selection in conjunction with
mutation is capable of being creative (depending on how you define
creative), especially if the process is repeated ad nauseum.

It might seem like I'm stressing a very minor point when I should be
pressing Johnson on more meaty topics. However, one of his main
arguments in _DoT_ is that selection cannot be creative. Then as
an illustration, he cites the moth example and stresses that both
color morphs of moths were always present and concludes that selection 
can only cause "local population fluctuations" (see page 27). He's 
allowing the definition of selection to slip when he discusses it.

When biologists speak of the creative power of selection they are
talking about _cumulative_ selection. (Someone has borrowed my
Dawkins at this point, but I recall him being explict about this
-- perhaps someone could check this out for me? I remember the
"Methinks it is like a weasel" discussion where he goes on and
on about how numerous small changes (mutations) filtered by
selection bring about a big change.)

So anyway, my point was going to be (and now is): Looking at a
single selective event and claiming it isn't creative enough to
be a mechanism of macroevolution is misleading. Natural selection
is (IMHO) the primary agent of evolutionary change, but it only
works when other mechanisms (primarily mutation) supply it with
genetic variation. The iterated process of mutation followed by
selection is what biologists claim to be creative, not a single
shift in gene frequencies as Johnson tries to portray it. (Read
chapter two of his book to see how he ignores this point until
the very end of the chapter, then drops it.)

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"
Newsgroups: talk.origins