To: All Msg #105, Jan3093 03:37PM Subject: Re: evidence for cumulative selection In my pre
From: Chris Colby
To: All Msg #105, Jan-30-93 03:37PM
Subject: Re: evidence for cumulative selection
Organization: animal -- coelomate -- deuterostome
From: firstname.lastname@example.org (Chris Colby)
In my previous post I tried to clearly explain the difference
between natural selection (by itself) and cumulative natural selection.
I then complained that I felt Johnson was scoring points in his
book by using "selection" to mean both. I then said that evidence for
cumulative selection came from two sources 1.) direct evidence of the
components and 2.) inferences from patterns seen in living systems.
(I should point out that I think the best evidence for common
descent and modification with descent (which would not necessarily have
to go together) comes from how traits are distributed across taxa (groups
of organisms).) Finally, I asked Johnson if he would like to discuss
some pertinent evidence. Since he seems to believe that the evidence
from (1.) above is, in and of itself, inconclusive; I suggested we
discuss evidence relating to (2.). Let's see how he responds.
In article <email@example.com> firstname.lastname@example.org
(Phillip Johnson) writes:
>A word search of the Chris Colby FAQ discloses that it, unlike
>the Johnson book, does not refer to "cumulative" selection.
Yep, I shouldn't have been so sloppy. The difference between my FAQ
and your book is; when I fix the sliding definitions, my arguments
will be better. If you clear up the terminology, your case looks
>does contain the following pertinent statements: First,
>"Macroevolution is cumulative microevolution."
Yes indeed it does say that. I happen to think that is true. Others
in related fields to mine (some paleontologists, for ex.) think
extra mechanisms such as species selection or species sorting are
necessary to explain macroevolution. This, as I have pointed out
in my FAQ and subsequent posts, is subject to debate.
>Second, "Natural selection
>is the only mechanism of adaptive evolution."
Natural selection, when supplied with genetic variation by
mutation or other sources, is the only accepted mechanism
of adaptive evolution. Other proposed mechanisms of adaptive
change (for example, inheritance of acquired characteristics)
have not stood up to scientific scrutiny. Recently, adaptive
(or directed) mutagenesis has been proposed to occur. I think
this will qualify as a mechanism of adaptive change although
I think it will be very limited in its importance compared to
selection. It is too soon to tell, however, so I'm waiting
before I make any sweeping changes in the FAQ -- I do mention
directed mutagenesis in the "mutation" section of my FAQ.
In short, if it is understood that selection needs genetic variation
to work on, and genetic variation is supplied by mutation(*);
I will certainly stand by the statement, "Natural selection is
the only mechanism of adaptive evolution."
To take our friends the moths as an example, at some time in
history black moths appeared. When conditions changed selection
acted and the population adapted. The adaptation could not have
occurred without the mutation, but it was natural selection that
increased the mean relative fitness of the population (i.e. made
it adapt to the environment).
(*) and gene flow and recombination
Since Mr. Johnson has yet to define creative, I'm not sure if he
is trying to equate adaptive with creative. Depending how creative
is defined, these may or may not overlap. A reasonable definition
of adaptive is a trait that increases the mean relative fitness of a
population. Sometimes adaptive is defined with natural selection in
the definition, along the lines of "something is adaptive if it is
favored by natural selection." Clearly, that would be a poor
choice of definitions in this context. On a side note, Lewontin
has a (SciAm?) article in the late 70's about the problems with
the term "adaptation" -- interesting, but beyond the scope of this
Instead of word-searching my posts for key phrases, how about
reading them for content and responding to the substance of the
arguments I am presenting? In _DoT_ you claim, "My purpose is to
examine the scientific evidence on its own terms,". Is this
still the case? Would you like to discuss either the evidence
for common descent or the evidence for modification with descent?
I have recently posted a lot of information pertaining to these
issues. Would you care to respond?
>Phillip E. Johnson
> School of Law, University of California, Berkeley CA 94720
Chris Colby --- email: email@example.com ---
"'My boy,' he said, 'you are descended from a long line of determined,
resourceful, microscopic tadpoles--champions every one.'"
--Kurt Vonnegut from "Galapagos"
E-Mail Fredric L. Rice / The Skeptic Tank