Bob, and everyone following this thread,
I started writing out a response throughout most of the day on Friday, then
left it until this morning. Now I see that I've missed several turns of
the dialogue! Please forgive if this is too little too late (or, as the
case may be, too much too late).
Bob Dehaan wrote:
> > I would be happy to take
> > macroevolution seriously if there were empirical evidence that natural
> > selection played a significant *creative* role in it.
And Howard Van Till responded:
>Let me suggest some modification of vocabulary here. I would say that
>natural selection does nothing whatsoever that is authentically *creative.*
>Rather, it acts as a positive feedback mechanism in the context of a search
>program. Briefly here is why I say this:
>
>The fundamental meaning of "to create" is "to give being to."
>
>To call natural selection *creative* is, I would say, to misuse the term in
>the same way as do the proponents of naturalism.
This is a perfect example of the ambiguity inherent in our modes of
description (See my upcoming Young Scientist Corner contribution). I
wouldn't go so far as Howard in saying that the word "creative" should
never be used to describe natural selection, but I agree with his point of
clarification. The word has to be understood in its appropriate context as
a descriptor rather than as a rigid (i.e., only one valid usage) definition.
Now, on to other things. Bob, I have been thinking a lot about how to
communicate both my criticisms (friendly, I assure you) of your top-down
phylogenesis idea and my answer to your questions regarding the role of
evolution in junk DNA (a question which you asked of me privately). I have
been slow to respond in part because I have been trying to accurately
understand your perspective. Your above statement is consistent with the
perception that I was forming of your perspective. In brief, I think that
you see natural selection as EVERYTHING and the ONLY THING in evolution as
a whole, and this unnecessarily clouds your interpretation of
evolution-related discussions. I agree with George M. that you seem to have
your reasoning a little backwards when you say that you'd be inclined to
believe macroevolution if there were better evidence for natural
selection. I believe several points may help us clarify the issues better.
1) Common ancestry and macroevolution.
I have argued in previous posts that the evidence is strong (unequivocal
even) for common ancestry. I'm not 100% sure where you fall on this point;
your articles suggest that you may accept this (how else could you discuss
top-down phylogenesis) at least back to the phylum level; on the other
hand, you mentioned in your post here that you are "not persuaded to accept
macroevolution or common ancestry". The patterns of homology (molecular
and morphological) plus the known mechanisms of inheritance are
sufficiently complex and particular in form so as to be SPECIFIC to descent
from common ancestors.
Now, If one accepts common ancestry as fact, then one NECESSARILY accepts
that there is a material, mechanistic continuity (unbroken connection or
descent) for living creatures AND that macroevolution has in fact
occurred. This does not say anything about what the mechanism is, only that
it exists. Somehow, we did in fact get here from there, materially and
mechanistically, i.e., evolutionarily. (I believe even Behe would agree to
this point). Bob, even if you personally want to draw a common ancestry
boundary line at the level of phyla, you are accepting a HUGE amount of
common ancestry (i.e., speciation and macroevolution of a diversity of
adaptations and forms) down from that level. Consideration of natural
selection supports this conclusion of common ancestry, but it is not
necessary to it. That's important in my line of argument.
If one does NOT accept common ancestry (or, speaking in terms of forward
time, speciation), then there is nothing left worth discussing with him/her
relating to evolution. Such a person has turned him/herself off to the
validity of my entire scientific discipline at such a fundamental level
that we are without any common ground. It becomes nonsensical, like
discussing the nature of cancer with a person who does not accept the
validity of medical science (which is based on the assumption that there is
a physical basis to physical ailments). Or like discussing sea navigation
with a person who does not accept that the world is a sphere. Or like
discussing how one got a genetic disease with a person who does not believe
in inheritance. Or, to draw an example from your own favorite topic, like
discussing ontogeny and development with a person who does not believe that
a zygote (in the appropriate environment) is endowed with sufficient
physical capabilities to become a mature organism. I have to conclude that
the person who does not accept common ancestry and speciation at levels
much deeper than "varieties" or "races" of a species (i.e., much deeper
than microevolution), simply has not examined the compelling manifold
evidence. (Here is one point where the patterns of mutation in "junk DNA"
verses highly functionally constrained DNA segments provides unequivocal
support for common ancestry -- I'll try to elaborate on this point when I
have some more time).
In other words (to summarize my first point), the issue of macroevolution
(i.e., whether or not it occurred) is NOT IDENTICAL to the issue of natural
selection as the mechanism able to effect this evolution. Bob, my
understanding is that your main beef is with the latter issue. Let me move on.
2) Natural selection as fact.
Macroevolution and natural selection are not identical, but they are
obviously intimately related. I hope that you accept the fact that natural
selection actually occurs, and that it will ALWAYS occur wherever there is
heritable variation and a limiting environment in which there is
differential survival and reproduction. Thus, if you accept common
ancestry (i.e., physical continuity of descent), then you must accept that
natural selection has always been operating in natural history. Therefore,
natural selection is AT LEAST PART of the overall mechanism by which
evolution has occurred. The "feedback mechanism" or "filter" of natural
selection is always present, and it will always lead to the realization of
adaptations (even in the form of new structures) as long as detectable
heritable variation is presented to it (and the vagaries of random drift do
not quench it first).
Here is one criticism I have of your reasoning in your "Top-down
phylogenesis" article. In discussing higher level taxa, you seem to forget
the fact that at every stage of history each taxon existed biologically as
a population of reproducing organisms, and as such were subject to natural
selection and all other aspects of population genetics (there is
significantly more functional (ontological) reality to species or
populations than to higher level taxonomic categories). Whatever else
MIGHT have been different in early biological history (e.g., more
unoccupied adaptive zones, less complicated food webs?, etc.), natural
selection was nevertheless operating then much as it is now. Even Marxist
macroevolutionists like Gould (who strive to show that natural selection by
the classical Darwinian sense of strictly gradual population genetic change
is not adequate) would acknowledge this point.
3) Natural selection as necessary for evolution.
Since natural selection actually occurs, this point almost goes without
saying. Yes, N.S. is necessary for the realization of the diversity of
living organisms (and their adaptations) we observe to have descended from
common ancestors. Whether or not we are talking about the origination of
entirely new structures (morphological or molecular) or the refinement of
pre-existing ones, N.S. was at some level and at most stages along the way
necessary to cull out deleterious mutations and keep each particular
"thread" of evolution "canalized" or "focused" along a currently successful
path. (Remember, however, that N.S. is not forward thinking; this is why I
used the word "currently" in that sentence; it is also why it is
appropriate in this context to describe evolution as "undirected and
purposeless").
4) Natural selection as entirely SUFFICIENT to account for all evolution,
even the "big" changes we label macroevolution.
Bob, if I'm correct, this is where you get off the bus. But while you
complain that N.S. has only been empirically demonstrated at the
microevolutionary level, I hope that you can appreciate that it is probably
impossible to fully empirically demonstrate any specific mechanism for
ancient evolutionary events. There is an epistemological gap there. We
can only go on the physical rules of interaction and inheritance that we
can demonstrate in the present and near-present, assume that those rules
applied in the past wherever the basic conditions are obviously met (i.e.,
reproducing populations, limited environment), and evaluate whether and how
they might have been sufficient to produce the patterns we see. As I
stated above, N.S. was certainly acting in the distant past. We know it
works very effectively in the present and recent evolutionary past (which
we can demonstrate empirically), so why not assume that it did so in the
more ancient past (which, for the components we can observe -- e.g.,
reproductive structures which prove that ancient creatures reproduced,
environmental variables, biogeography, etc. -- it is consistent with)?
As an aside. You cited several empirical studies of N.S. in the near
present. Let me suggest a couple of others from the plant literature that
involve "recreating" a speciation event ecologically and genetically. I
don't have time to review the details here; perhaps I will do so more
later. I mention them because they are examples of genetic "dissection" of
the speciation event (with major morphological and ecological change in
adaptation), and thereby demonstration of a "viable genetic trajectory"
between the two diverse entities.
The first is by Doug Schemske et al. (Genetics. 1998 May;149(1):367-82;
Proc Natl Acad Sci U S A. 1999 Oct 12;96(21):11910-5; see the later article
online at http://www.pnas.org/cgi/content/full/96/21/11910 ).
The second is by Doebley et al. (Nature. 1999 Mar 18;398(6724):236-9;
Trends Genet. 1998 Aug;14(8):327-32; Trends Genet. 1992 Sep;8(9):302-7;
Genetics. 1991 Sep;129(1):285-95.).
Now, let me go back to my last statement in part 2. The big condition
there is that "detectable heritable variation" must be produced. In one
sense, then, the selection side of N.S. is not the problem for you, but
rather the generation of appropriate variation. Your real question is "Can
mutations occur which affect development in significant ways to so as to
produce entirely new structures?" (Let me first warn you that I'm not a
developmental biologist, and my area is plants, so I no big expert on the
your metazoa problem). First, I think that even in the Cambrian, the
diversification was not instantaneous; 10s of millions of years were
probably involved in the evolution of all relevant major body
structures. When one considers the range of changes that have occurred in
organisms in the most recent 50 million years, the ancient stuff doesn't
seem unlikely. Second, let me provide a "just-so" explanation (again, this
isn't my area of expertise, I admit). Significant morphological changes are
possible via fairly small genetic mutations and nevertheless remain stable
developmentally (see plant examples above). Furthermore, in the aquatic
environment of the ancient world, such "macromutations" were likely less of
a burden (than they would be on land, for example, where factors such as
gravity and desiccation pose major constraining forces to organisms). This
means that there could have been a more "open" mutational viability space
at that time and in that environment. Natural selection was still
operating and important, but many structures could exist for a time as
nearly neutral (nondeleterious) features, in a sense "waiting in reserve"
until they happen to amount to some use, at which time they would be
"refined" by N.S.
I need to move on. Is N.S. sufficient to explain all evolution? Well, yes
and no. It is certainly essential, and it's role should not be
underestimated. This is why George was correct in his original statement
about the reality of macroevolution including a significant role for
N.S. As long as there has been living organisms (or even mere chemicals)
that generate and express heritable variation in a limiting environment,
natural selection will be an important part of determining the system's
evolution through time. On the other hand, natural selection does not
stand alone as the only all-sufficient mechanism for generating the
patterns of biological variation we observe in nature. As I alluded to
earlier, the interesting thing about junk DNA, and in fact most of
molecular level variation, is that it is largely NEUTRAL. At the DNA
level, evolution can be accurately modeled as if mutations were neutral
with respect to phenotype, (i.e., that they have no selective advantage or
disadvantage). Lot's of genetic change just doesn't matter. It falls
below the radar of detection for natural selection operating at the
organismal level. This allows a background or "null" case against which
the operation of natural selection can be measured (quantified) at specific
DNA nucleotides positions in which mutations are known to have selective
effects. Thus, it is the fact that selection does NOT "see" everything
that is important in generating certain aspects of observed biotic
variation. It has to do with targets of selection and units of selection.
Is N.S. sufficient to explain evolution?
Taken together with accompanying mechanistic factors (generation of
variation by mutation, particular modes of inheritance, random genetic
drift and occasional "catastrophic" sampling effects, ecological factors,
etc), I believe that it is a very reasonable assumption that natural
selection (operating at a variety of levels) is sufficient to explain
biological evolution from a single common ancestor. We KNOW that descent
with modification occurs, that modification comes primarily by a variety of
mutations in the genetic material, and that natural selection operates
effectively whenever the basic conditions are met. We KNOW that life on
earth is related by common ancestry. Thus, natural selection (in the broad
sense just described) is the only present mechanism available to
investigate directly and assume interpretively.
Of course, God COULD have interceded to make certain unlikely and necessary
mutations happen in order to keep things moving according to his intent, in
which case one would have to conclude that there were a few exceptions to
random mutation getting all the work done. Even so, N.S. would have always
operated on that mutation. I really don't have a problem with Behe and
other IDers investigating the organic or chemical complexity of the
universe in search of patterns which can only be explained by direct Divine
action (DDA). I think they're barking up the wrong tree, however, since I
think God from the get-go gifted his creation (which included a role for
mutational exploration of "design space" and natural selection) to be
fruitful for his purposes. I welcome development of ID ideas, especially
the production of meaningful ways of detecting "special" or "non-pregifted"
mutation, and then real examples that meet these criteria. The burden of
proof is on them, however, since evolution has ALL KNOWN mechanisms in its
favor.
What I do have trouble with is the antagonism that IDology fuels against
legitimate evolutionary biology. I especially take issue with it being used
as a "wedge of truth" to form an evidentialist apologetic for
Christianity. This is the plain sense that every Christian layperson gets
from the ID propaganda and CT media coverage. This is very dangerous; I
have sat in church listening to a recent seminary graduate slam evolution
from the pulpit and promote "great thinkers" (P. Johnson) and "one of the
world's foremost molecular biologists" (Behe) on "our" behalf. Meanwhile I
sit there in the pew with a Ph.D. in evolutionary biology, trying to figure
out how this helps anyone in their Christian life. I am glad that you,
Bob, do not subscribe to an evidentialist "use" of ID. That gives us
enough of a common ground to discuss these things in a most friendly manner.
I must end here. Sorry if I left certain things unexplained or weakly
substantiated.
Doug Hayworth
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