On Tue, 03 Mar 1998 01:58:13 -0800, Cliff Lundberg wrote:
>SJ>But IMHO, the *real* problem that was behind Darwin's ambiguity and the
>>modern-day argument between the "strict" and "pluralist" Darwinists
>>is that step-by-tiny-incremental-step natural selection is the *only*
>>naturalistic way, even in principle, to develop life's complex designs,
>>yet the evidence from the fossil record is that it didn't happen
>>that way.
CL>Why would a macromutation be *in principle* not natural(istic)?
First we need to distinguish between what Dawkins calls "Boeing 747
macromutations" and "Stretched DC8 macromutations":
"..it may be helpful to draw a distinction between two kinds of
hypothetical macromutation, both of which appear to be ruled out by
the complexity argument but only one of which, in fact, is ruled out
by the complexity argument. I label them, for reasons that will
become clear, Boeing 747 macromutations and Stretched DC8
macromutations. Boeing 747 macromutations are the ones that really
are ruled out by the complexity argument just given. They get their
name from the astronomer Sir Fred Hoyle...He compared natural
selection, in its alleged improbability, to a hurricane blowing through
a junkyard and chancing to assemble a Boeing 747...The idea of a
single macromutation's giving rise to a fully functioning eye with the
properties listed above, where there was only bare skin before, is,
indeed, just about as improbable as a hurricane assembling a Boeing
747. This is why I refer to this kind of hypothetical macromutation as
a Boeing 747 macromutation. Stretched DC8 macromutations are
mutations that, although they may be large in the magnitude of their
effects, they out not to be large in terms of their complexity. The
Stretched DC8 is an airliner that was made by modifying an earlier
airliner, the DC8. It is like a DC8, but with an elongated fuselage. It
was an improvement at least from one point of view, in that it could
carry more passengers than the original DC8. The stretching is a large
increase in length, and in that sense is analogous to a macromutation.
More interestingly, the increase in length is, at first sight, a complex
one. To elongate the fuselage of an airliner, it is not enough just to
insert an extra length of cabin tube. You also have to elongate
countless ducts, cables, air tubes and electric wires. You have to put
in lots more seats, ashtrays, reading lights, 12- channel music
selectors and fresh-air nozzles. At first sight there seems to be much
more complexity in a Stretched DC8 than there is in an ordinary
DC8, but is there really? The answer is no, at least to the extent that
the 'new' things in the stretched plane are just 'more of the same'."
(Dawkins R., "The Blind Watchmaker", 1986, pp234-235)
Dawkins goes on to give the example of snakes and their vertebrae:
"Snakes, for instance, all have many more vertebrae than their
ancestors. We could be sure of this even if we didn't have any fossils,
because snakes have many more vertebrae than their surviving
relatives. Moreover, different species of snakes have different
numbers of vertebrae, which means that vertebral number must have
changed in evolution since their common ancestor, and quite often at
that. Now, to change the number of vertebrae in an animal, you need
to do more than just shove in an extra bone. Each vertebra has,
associated with it, a set of nerves, a set of blood vessels, a set of
muscles etc., just as each row of seats in an airliner has a set of
cushions, a set of head rests, a set of headphone sockets, a set of
reading-lights with their associated cables etc. The middle part of the
body of a snake, like the middle part of the body of an airliner, is
composed of a number of segments, many of which are exactly like
each other, however complex they all individually may be. Therefore,
in order to add new segments, all that has to be done is a simple
process of duplication. Since there already exists genetic machinery
for making one snake segment - genetic machinery of great
complexity, which took many generations of step-by-step, gradual
evolution to build up - new identical segments may easily be added by
a single mutational step. If we think of genes as 'instructions to a
developing embryo', a gene for inserting extra segments may read,
simply, 'more of the same here'. I imagine that the instructions for
building the first Stretched DC8 were somewhat similar." (Dawkins,
1986, p235)
Dawkins comcludes that "Stretched DC8" macromutations are "not true
macromutations":
"...it is obvious that there must have been cases when an offspring
snake had at least one whole vertebra more than its parents did. This
means that it had a whole extra set of nerves, blood vessels, muscle
blocks, etc. In a sense, then, this snake was a macro-mutant, but only
in the weak 'Stretched DC8' sense. It is easy to believe that individual
snakes with half a dozen more vertebrae than their parents could have
arisen in a single mutational step. The 'complexity argument' against
saltatory evolution does not apply to Stretched DC8 macromutations
because, if we look in detail at the nature of the change involved, they
are in a real sense not true macromutations at all. They are only
macromutations if we look, naively, at the finished product, the adult.
If we look at the processes of embryonic development they turn out
to be micromutations, in the sense that only a small change in the
embryonic instructions had a large apparent effect in the adult. The
same goes for antennapaedia in fruitflies and the many other so-called
'homeotic mutations'. (Dawkins R., 1986, p236)
So by "macromutations", we are only talking about "Boeing 747
macromutations". There are several reasons why "Boeing 747
macromutations" (hereafter simply "macromutations") would "be in
principle* not natural(istic)":
1. A major macromutation would be indistinguishable from a miracle:
"Darwin was particularly anxious to avoid the need for any
"saltations"-sudden leaps by which a new type of organism appears in
a single generation. Saltations (or systemic macromutations, as they
are often called today) are believed to be theoretically impossible by
most scientists, and for good reason. Living creatures are extremely
intricate assemblies of interrelated parts, and the parts themselves are
also complex. It is impossible to imagine how the parts could change
in unison as a result of chance mutation. In a word (Darwin's word), a
saltation is equivalent to a miracle. At the extreme, saltationism is
virtually indistinguishable from special creation. If a snake's egg were
to hatch and a mouse emerged we could with equal justice classify
the event as an instance of evolution or creation. Even the sudden
appearance of a single complex organ, like an eye or wing, would
imply supernatural intervention. Darwin emphatically rejected any
evolutionary theory of this sort, writing to Charles Lyell that: `If I
were convinced that I required such additions to the theory of natural
selection, I would reject it as rubbish...I would give nothing for the
theory of natural selection, if it requires miraculous additions at any
one stage of descent.' (Darwin F., ed., "The Life and Letters of
Charles Darwin", 1888, ii:210). (Johnson P.E., "Darwin on Trial",
1993, pp32-33)
The whole point of the theory of evolution was to get away from
miracles. If evolution happened by major mysterious jumps, then
all the normal Darwinian mechanisms like natural selection would
be largely irrelevant, and there would be no scientific *theory* of
macroevolution:
"We can see from these examples why neo-Darwinism retains its
status as textbook orthodoxy despite all the difficulties and even the
imputations of moribundity. If neo-Darwinist gradualism were
abandoned as incapable of explaining macroevolutionary leaps and
the origin of complex organs, most biologists would still believe in
evolution (Goldschmidt and Grasse never doubted that evolution had
occurred), but they would have no *theory* of evolution. Materialist
scientists are full of scorn for creationists who invoke an invisible
creator who employed supernatural powers that cannot be observed
operating in our own times. If evolutionary science must also rely
upon mystical guiding forces or upon genetically impossible
transformations, a philosophical materialist like Charles Darwin
would call it rubbish." (Johnson P.E., "Darwin on Trial", 1993, pp43-
44)
2. Even if a macromutation were to occur, it would be unable to find
a mate:
"There are very good reasons for rejecting all such saltationist
theories of evolution. One rather boring reason is that if a new
species really did arise in a single mutational step, members of the
new species might have a hard time finding mates."
(Dawkins, 1986, p231)
"We can well imagine such a non-Darwinian theory of discontinuous
change-profound and abrupt genetic alteration luckily (now and then)
making a new species all at once. Hugo de Vries, the famous Dutch
botanist supported such a theory early in this century. But these
notions seem to present insuperable difficulties. With whom shall
Athena born from Zeus's brow mate? All her relatives are members of
another species." (Gould S.J., "The Return of the Hopeful Monster",
"The Panda's Thumb", 1980, p158)
3. There is an inverse relationship between a mutation's size and
its probability of survival, as Simpson, one of the co-founders of
Neo-Darwinism pointed out:
"The chance that a mutation will be favored by selection and the
chance that it will or can be integrated into a genetic system as a
whole are inversely related to the effect of the mutation on the
organism. If this effect is really radical, comparable, say, to the
difference between one family and another (a fortiori, to that between
higher categories) in the recent fauna, the chances that the mutation
will really take, so to speak, and lead to an evolutionary progression
are so small as to be almost negligible." (Simpson G.G., "The
Meaning of Evolution:, 1949, p234).
Dawkins gives an analogy of random adjustments to an already
well-adjusted microscope:
"But I find this reason [lack of a mate] less telling and interesting than
two others which have already been foreshadowed in our discussion
of why major jumps across Biomorph Land are to be ruled out. The
first of these points was put by the great statistician and biologist R.
A. Fisher, whom we met in other connections in previous chapters.
Fisher was a stalwart opponent of all forms of saltationism, at a time
when saltationism was much more fashionable than it is today, and he
used the following analogy. Think, he said, of a microscope which is
almost, but not quite perfectly, in focus and otherwise well adjusted
for distinct vision. What are the odds that, if we make some random
change to the state of the microscope (corresponding to a mutation),
we shall improve the focus and general quality of the image? Fisher
said: `It is sufficiently obvious that any large derangement will have a
very small probability of improving the adjustment, while in the case
of altcrations much less than the smallest of those intentionally
effected by thc maker or the operator, the chance of improvement
should be almost exactly one half.'... Remember that we are assuming
the microscope to be almost in correct focus before we start.
Suppose that the lens is slightly lower than it ought to be for perfect
focus, say a tenth of an inch too close to the slide. Now if we move it
a small amount, say a hundredth of an inch, in a random direction,
what are the odds that the focus will improve? Well, if we happen to
move it down a hundredth of an inch, the focus will get worse. If we
happen to move it up a hundredth of an inch, the focus will get better.
Since we are moving it in a random direction, the chance of each of
these two eventualities is one half. The smaller the movement of
adjustment, in relation to the initial error, the closer will the chance of
improvement approach one half...But now, suppose we move the
microscope tube a large distance - equivalent to a macromutation -
also in a random direction; suppose we move it a full inch. Now it
doesn't matter which direction we move it in, up or down, we shall
still make the focus worse than it was before." (Dawkins R., 1986,
pp231-232)
4. While stastically macromutations are possible, they are so rare as
to be virtually impossible:
"The other general reason for not believing in true saltation is also a
statistical one, and its force also depends quantitatively on how macro
is the macromutation we are postulating. In this case it is concerned
with the complexity of evolutionary changes. Many, though not all, of
the evolutionary changes we are interested in are advances in
complexity of design. The extreme example of the eye, discussed in
earlier chapters, makes the point clear. Animals with eyes like ours
evolved from ancestors with no eyes at all. An extreme saltationist
might postulate that the evolution took place in a single mutational
step. A parent had no eye at all, just bare skin where the eye might
be. He had a freak offspring with a fully developed eye, complete
with variable focus lens, iris diaphragm for 'stopping down', retina
with millions of three-colour photocells, all with nerves correctly
connected up in the brain to provide him with correct, binocular,
stereoscopic colour vision. In the biomorph model we assumed that
this kind of multi- dimensional improvement could not occur. To
recapitulate on why that was a reasonable assumption, to make an
eye from nothing you need not just one improvement but a large
number of improvements. Any one of these improvements is pretty
improbable by itself, but not so improbable as to be impossible. The
greater the number of simultaneous improvements we consider, the
more improbable is their simultaneous occurrence. The coincidence
of their simultaneous occurrence is equivalent to leaping a large
distance across Biomorph Land, and happening to land on one
particular, predesignated spot. If we choose to consider a sufficiently
large number of improvements, their joint occurrence becomes so
improbable as to be, to all intents and purposes, impossible."
(Dawkins, 1986, p233)
5. The final point is that even if macromutations do occur, the
question still arises whether they play any significant role in
evolution:
"Macromutations - mutations of large effect - undoubtedly occur.
What is at issue is not whether they occur but whether they play a
role in evolution; whether, in other words, they are incorporated into
the gene pool of a species, or whether, on the contrary, they are
always eliminated by natural selection. A famous example of a
macromutation is 'antennapaedia' in fruitflies. In a normal insect the
antennae have something in common with the legs, and they develop
in the embryo in a similar way. But the differences are striking as
well, and the two sorts of limb are used for very different purposes:
the legs for walking; the antennae for feeling, smelling and otherwise
sensing things. Antennapaedic flies are freaks in which the antennae
develop just like legs. Or, another way of putting it, they are flies that
have no antennae but an extra pair of legs, growing out of the sockets
where the antennae ought to be. This is a true mutation in that it
results from an error in the copying of DNA. And it breeds true if
antennapaedic flies are cosseted in the laboratory so that they survive
long enough to breed at all. They would not survive long in the wild,
as their movements are clumsy and their vital senses are impaired."
(Dawkins, 1986, p230)
CL>Is it so hard to imagine a pre-Cambrian epoch, a world without
>well-formed predators, in which bizarre macromutations among
>simple organisms might be viable?
See above. Macromutations fail, even without predators.
If we want imaginary worlds, then we turn to science *fiction*
writers. Science is supposed to be about *testable* theories.
Steve
--------------------------------------------------------------------
Stephen E (Steve) Jones ,--_|\ sejones@ibm.net
3 Hawker Avenue / Oz \ Steve.Jones@health.wa.gov.au
Warwick 6024 ->*_,--\_/ Phone +61 8 9448 7439
Perth, West Australia v "Test everything." (1Thess 5:21)
--------------------------------------------------------------------