|
 |
William Paley Institute
for
Intelligent Design |
|
|
|
|
|
|
|
Blind Evolution or Intelligent Design?
by Michael J. Behe
American Museum of Natural History
April 23, 2002
Talk delivered at the American Museum of Natural History, 23 April 2002 at a
discussion titled Blind Evolution or Intelligent Design? The participants
included ID proponents William A. Dembski and Michael J. Behe as well as
evolutionists Kenneth R. Miller and Robert T. Pennock. Eugenie C. Scott
moderated the discussion. An introduction was given by National History Editor,
Richard Milner. For coverage of this debate, see Scott Stevens' article in The
Cleveland Plains Dealer.
Thanks very much, Dr. Scott! Its great to be back in New York City. I taught at
Queens College and City University for three years in the early
nineteen-eighties; my wife grew up on Cambreleng Avenue near 187th Street in the
Bronx and our first child was born here, so New York holds many happy memories
for our family.
My talk will be divided into four parts: first, a sketch of the argument for
design; second, common misconceptions about the mode of design; third,
misconceptions about biochemical design; and finally, discussion of the future
prospects of design. Before I begin, however, Id like to emphasize that the
focus of my argument will not be descent with modification, with which I agree.
Rather, the focus will be the mechanism of evolutionhow did all this happen, by
natural selection or intelligent design? My conclusion will not be that natural
selection doesnt explain anything; Rather, the conclusion will be that natural
selection doesnt explain everything.
So, lets begin with a sketch of the design argument. In the Origin of Species,
Darwin emphasized that his was a very gradual theory; natural selection had to
work by numerous, successive, slight modifications to pre-existing structures.
However, irreducibly complex systems seem quite difficult to explain in
gradual terms. What is irreducible complexity? Ive defined the term in various
places, but its easier to illustrate what I mean with the following example:
the common mousetrap. A common mechanical mousetrap has a number of interacting
parts that all contribute to its function, and if any parts are taken away, the
mousetrap doesnt work half as well as it used to, or a quarter as wellthe
mousetrap is broken. Thus it is irreducibly complex.
Suppose we wanted to evolve a mousetrap by something like a Darwinian process.
What would we start with? Would we start with a wooden platform and hope to
catch mice inefficiently? Perhaps tripping them? And then add, say, the holding
bar, hoping to improve efficiency? No, of course not, because irreducibly
complex systems only acquire their function when the system is essentially
completed. Thus irreducibly complex systems are real headaches for natural
selection because it is very difficult to envision how they could be put
together that is, without the help of a directing intelligence by the
numerous, successive, slight modifications that Darwin insisted upon.
Irreducibly complex biological systems would thus be real challenges to
Darwinian evolution.
Yet modern science has discovered irreducibly complex systems in the cell. An
excellent example is the bacterial flagellum which is literally an outboard
motor that bacteria use to swim. The flagellum has a large number of parts that
are necessary for its functiona propeller, hook, drive shaft, and more.
Thorough studies shows it requires 30-40 protein parts. And in the absence of
virtually any of those parts, the flagellum doesnt work, or doesnt even get
built in the cell. Its gradual evolution by unguided natural selection therefore
is a real headache for Darwinian theory. I like to show audiences this picture
of the flagellum from a biochemistry textbook because, when they see it, they
quickly grasp that this is a machine. It is not like a machine, it is a real
molecular machine. Perhaps that will help us think about its origin.
I have written that not only is the flagellum a problem for Darwinism, but that
it is better explained as the result of design deliberate design by an
intelligent agent. Some of my critics have said that design is a religious
conclusion, but I disagree. I think it is wholely empirical, that is, the
conclusion of design is based on the physical evidence along with an
appreciation for how we come to a conclusion of design. To illustrate how we
come to a conclusion of design, lets look at the following. This is a Far Side
cartoon by Gary Larson showing a troop of jungle explorers, and the lead
explorer has been strung up and skewered. Now, everyone in this room looks at
this cartoon and you immediately realize that the trap was designed. But how do
you know that? How do you know the trap was designed? Is it a religious
conclusion? Probably not. You know its designed because you see a number of
very specific parts acting together to perform a function; you see something
like irreducible complexity or specified complexity.
Now I will address common misconceptions about the mode of design, that is, how
design may have happened.
My book, Darwins Black Box, in which I flesh out the design argument, has been
widely discussed in many publications. What have other scientists said about it?
Well, theyve said many thingsnot all flatteringbut the general reaction is
well summarized in a recent book The Way of the Cell, published last year by
Oxford University Press, and authored by Colorado State University biochemist
Franklin Harold, who writes, We should reject, as a matter of principle, the
substitution of intelligent design for the dialogue of chance and necessity
(Behe 1996); but we must concede that there are presently no detailed Darwinian
accounts of the evolution of any biochemical system, only a variety of wishful
speculations. Let me take a moment to emphasize Harolds two points. First, he
acknowledges that Darwinists have no real explanations for the enormous
complexity of the cell, only hand-waving speculations, more colloquially known
as Just-So stories.how the rhinoceros got its horn; how the bacterium got its
flagellum. I find this an astonishing admission for a theory that has dominated
biology for so long. Second, apparently he thinks that there is some principle
that forbids us from investigating the idea of intelligent design, even though
design is an obvious idea that quickly pops into your mind when you see a
drawing of the flagellum or other complex biochemical systems. But what
principle is that?
I think the principle boils down to this: ?Design appears to point strongly
beyond nature. It has philosophical and theological implications, and that makes
many people uncomfortable. But any theory that purports to explain how life
occurred will have philosophical and theological implications. For example, the
Oxford biologist Richard Dawkins has famously said that Darwin made it possible
to be an intellectually-fulfilled atheist. Ken Miller has written that [God]
used evolution as the tool to set us free. Stuart Kauffman, a leading
complexity theorist, thinks Darwinism cannot explain all of biology, and thinks
that his theory will somehow show that we are at home in the universe. So all
theories of origins carry philosophical and theological implications.
But how could biochemical systems have been designed? Did they have to be
created from scratch in a puff of smoke? No. The design process may have been
much more subtle. It may have involved no contravening of natural laws. Lets
consider just one possibility. Suppose the designer is God, as most people would
suspect. Well, then, as Ken Miller points out in his book, Finding Darwins God,
a subtle God could cause mutations by influencing quantum events such as
radioactive decay, something that I would call guided evolution. That seems
perfectly possible to me. I would only add, however, that that process would
amount to intelligent design, not Darwinian evolution.
Now lets look at common misconceptions about biochemical design.
Some Darwinists have proposed that a way around the problem of irreducible
complexity could be found if the individual components of a system first had
other functions in the cell. For example, consider a hypothetical example such
as pictured here, where all of the parts are supposed to be necessary for the
function of the system. Might the system have been put together from individual
components that originally worked on their own? Unfortunately this picture
greatly oversimplifies the difficulty, as I discussed in my book, Darwins Black
Box. Here analogies to mousetraps break down somewhat, because the parts of the
system have to automatically find each other in the cell. They cant be arranged
by an intelligent agent, as a mousetrap is. To find each other in the cell,
interacting parts have to have their surfaces shaped so that they are very
closely matched to each other. Originally, however, the individually-acting
components would not have had complementary surfaces. So all of the interacting
surfaces of all of the components would first have to be adjusted before they
could function together. And only then would the new function of the composite
system appear. Thus the problem of irreducibility remains, even if individual
components separately have their own functions.
Another area where one has to be careful is in noticing that some systems with
extra or redundant components may have an irreducibly complex core. For example,
a car with four spark plugs might get by with three or two, but it certainly
cant get by with none. Rat traps often have two springs, to give them extra
strength. They can still work if one spring is removed, but they cant work if
both springs are removed. Thus in trying to imagine the origin of a rat trap by
Darwinian means, we still have all the problems we had with a mousetrap. A
cellular example of redundancy is the hugely-complex eukaryotic cilium, shown
here in cross-section, which has multiple copies of a number of components, yet
needs at least one copy of each to work, as I pictured in my book.
Many other criticisms have been made against intelligent design. I have
responded to a number of them at the following locations.
I will now discuss how I view the future prospects of a theory of intelligent
design. I see them as very bright indeed. Why? Because the idea of intelligent
design has advanced, not primarily because of anything I or any individual has
done. Rather, its been the very progress of science itself that has made
intelligent design plausible. Fifty years ago much less was known about the
cell, and it was much easier then to think that Darwinian evolution was true.
But with the discovery of more and more complexity at the foundation of life,
the idea of intelligent design has gained strength. That trend is continuing. As
science pushes on, the complexity of the cell is not getting any less; on the
contrary, it is getting much greater. For example, a recent issue of the journal
Nature carried the most detailed analysis yet of the total protein complement of
yeastthe so-called yeast proteome. The authors point out that most proteins
they investigated in the cell function as multiprotein complexesnot as solitary
proteins as scientists had long thought. In fact they showed that almost fifty
pecent of the proteins in the cell function as complexes of a half dozen or
more, such as the polyadenylation machinery shown in this figure from the paper.
To me, this implies that irreducible molecular machinery is very likely going to
be the rule in the cell, not the exception. We will probably not have to wait
too long to see.
Another example comes from a paper published in the Journal of Molecular Biology
two years ago, which showed that some enzymes have only a limited ability to
undergo multiple changes in their amino acid sequence, even when the enzymes
function alone, as single proteins, and even when the changes are very
conservative ones. This led the author to caution that homologues sharing less
than about two-thirds sequence identity should probably be viewed as distinctive
designs with their own optimizing features. The author pictured such proteins
as near-islands of function, virtually isolated from neighboring protein
sequences. This may mean that even individual proteins from separate species
that are similar but not identical in their amino acid sequence might not have
been produced by a Darwinian processes, as most scientists thought, and as even
I was willing to concede. Perhaps even I give too much unearned credit to
Darwinian theory.
Finally, to show what research questions might be asked by a theory of
intelligent design, Id like to briefly describe some of my own recent work.
This is the title slide of a seminar I gave six weeks ago to the biotechnology
group at Sandia National Laboratory. The title, Modeling the evolution of
protein binding sites: probing the dividing line between natural selection and
intelligent design, points to a question Im very interested in exploring. If
you are someone like myself who thinks that some things in biology are indeed
purposely designed, but that not all things are designed, then a question which
quickly arises is, where is the broad dividing line between design and
unintelligent processes? I think that question has to be answered at the
molecular level, particularly in terms of protein structure.
Drawings of the bacterial flagellum picture proteins as bland spheres or ovals,
but each protein in the cell is actually very complex. This ribbon drawing of
bovine pancreatic trypsin inhibitor gives a little taste of that complexity.
Now, proteins are polymers of amino acid residues, and some structural features
of proteins require the participation of multiple residues. For example, this
yellow link is called a disulfide bond. A disulfide bond requires two cysteine
residues just one cysteine residue cant form such a bond. Thus, in order for
a protein that did not have a disulfide bond to evolve one, several changes in
the same gene first have to occur. Thus in a real sense the disulfide bond is
irreducibly complex, although not nearly to the same degree of complexity as
systems made of multiple proteins.
The problem of irreducibility in protein features is a general one. Whenever a
protein interacts with another molecule, as all proteins do, it does so through
a binding site, whose shape and chemical properties closely match the other
molecule. Binding sites, however, are composed of perhaps a dozen amino acid
residues, and binding is generally lost if any of the positions are changed. One
can then ask the question, how long would it take for two proteins, that
originally did not interact, to evolve the ability to bind each other by random
mutation and natural selection, if binding only occurs when all positions have
the correct residue in place?
Although it would be difficult to experimentally investigate this question, the
process can be simulated on a computer. Here is a sample of the data I have
generated over the past year or so. The filled circles are data points from a
number of simulations which were all fit by the following equation, the details
of which I will not bother you with here. These results were presented at the
meeting of the Protein Society last summer in Philadelphia.
In the next slide the log of the expected time to generate what I call
irreducibly complex protein features is shown as a function of the log of the
population size and the log of the probability of the feature. The yellow dot is
the time expected to generate a new disulfide bond in a protein that did not
have one if the population size is a hundred million organisms. The expected
time is roughly a million generations. The red dot shows that the expected time
needed to generate a new protein binding site would be a hundred million
generations. Using data from these simulations as well as Bill Dembskis concept
of probabilistic resources, we can come to several broad, tentative conclusions:
1) that undirected irreducibly complex mutations cannot have been regularly
involved in the evolution of large animalsthe time frame would be too long; and
2) that undirected IC systems of the complexity of two or more protein binding
sites cannot have been regularly involved in the evolution of vertebrates. This
work assumed that all mutations were neutral. Future work could investigate such
questions as, what if intermediate mutations are selected against? and what
happens if there is competition between IC mutations and single-site mutations?
The broad motivation behind this work is to start getting some good numbers to
plug into Bill Dembskis explanatory filter, to try to come to a reasoned
conclusion about where in nature design leaves off.
In summary, I want to leave you with four take-home points: 1) that the question
is open: no other scientific theory has yet explained the data; 2) that
intelligent design is an empirical hypothesis that flows easily from the data,
as you can tell by looking at a drawing of the flagellum; 3) that there is no
principle that forbids our considering design; and best of all, 4) that there
are exciting research questions that can be asked within a design framework.
|
|
|
Promoting an
Understanding of the Intelligent Design of the Universe
|
|