>
> The evidence [that the moths were disoriented] is: they settled
> on tree trunks, where they do not naturally settle!
>
This is not evidence; it is rather an interpretation based on subjective
anthropormorphism as I described before, coupled with an apparent definition
of disorientation as doing something that is not natural. As such, if moths
settling on tree trunks instead of branches is not unnatural, then the moths
cannot be said to be disoriented. Based on the evidence presented by Majerus
in his book, settling on tree trunks is not usual, but it is not unnatural.
The evidence shows that, while they may do so infrequently, the moths will,
of their own accord, settle on tree trunks as well as branches. Since they
will do so on their own, it is no longer possible to claim that doing so is
"not natural" and therefore a case of disorientation. Your assumption of
disorientation is based more on wishful thinking and anthropormorphic empathy
than on hard data.
>
> I think Majerus' comments are very important here:
> "....it has become obvious that much of both the experimental and
> theoretical work suffers from artificiality. In many experiments,
> moths are placed into artificial situations, which may affect their
> own behaviour or that of their predators. For example, in most
> predation experiments peppered moths have been positioned on vertical
> tree trunks, despite the fact that they rarely chose such surfaces to
> rest upon in the wild." (page 116).
>
And yet Majerus does not consider this problem significant enough to doubt
the evidence derived from these experiments, since elsewhere in his book he
clearly states that natural selection by bird predation is the most valid
explanation for industrial melanism. That suggests that you are quoting
Majerus out of context here, trying to portray him as critical of
experimental procedures that in fact he probably describes as being necessary
for a successful field experiment.
>
> > The film itself may have been made under "unnatural" conditions,
> > but it was meant to document and illustrate what Kettlewell and
> > Tinbergen were seeing on a regular basis. .. ..
>
> No one is denying that birds eat moths. This is not the point I am
> arguing.
>
Your original statement was: "Kettlewell and Tinbergen's film was not
'natural' predation. My understanding is that the moths were disoriented -
having been released in the day time in a sluggish state. (If this unnatural
situation has been the trigger for an increasing perception that bird
predation is important, it would be wise for lepidopterists and
ornithologists to check that the mistake has not been repeated in later
'observations and experiments')." It sounds very much to me like you **are**
questioning that bird predation has a role in industrial melanism, on the
basis that the Kettlewell/Tinbergen film represented an "unnatural
situation". I was trying to point out that the situation could not have been
unnatural if it documented and illustrated what they were observing on a
regular basis.
>
> > Bats are indeed major predators of moths (probably more so than
> > birds, but not by much), but because they locate and capture prey
> > using sound rather than sight, their "relative importance" with
> > regard to industrial melanism would be very slight. .. .. So
> > while bats probably eat more moths than birds do, they would eat
> > both color phases indescriminantly; with the evidence we have,
> > birds are the most likely predator to cause the industrial
> > melanism affect.
>
> There is an element here of reaching concusions via "logical"
> argument, rather than via empirical investigation. This makes the PM
> even worse as a textbook example: who needs to do experiments? "Using
> the tools Darwin has provided, we can reconstruct the melanism story
> without going into the field and doing the hard work."
>
Again your original words were: "Perhaps we ought to be enquiring about the
relative importance of other predators - such as bats." The question then
becomes, what do you mean by relative importance. If you meant the relative
importance of other creatures as simply moth predators, there is no dispute
that bats and other insectivorous mammals, spiders and reptiles/amphibians
are significant predators of moths. But as you point out, this is not the
question. The real question is, what is the relative importance of these
predators with regard to industrial melanism? That question only makes sense
if you accept that some form of selective predation is the chief cause of
industrial melanism, and that in turn makes sense only if you accept that the
selectivity is visually oriented. Of the four major groups of moth
predators, which hunt by sight? The answer is birds, some spiders and
reptiles/amphibians. Which is most likely to have the greatest affect? The
answer is birds, by virtual of numbers and level of hunting activity. Does
the evidence so far obtained support this conclusion? The answer is yes.
Does that mean we need not test any other option? The answer is no. But
until we do test for these other options, the general principle established
by the evidence we have, namely natural selection based on selective
predation by birds, is still the most valid explanation. The fact that this
conclusion is based as much on logical argument as it is on empirical
evidence does not detract either from its validity or its explanatory power.
>
> > > 3. We have almost no information about the peppered moth
> > > predators in the natural state, nor which is the most important.
> >
> > We have no *direct* evidence, but the indirect evidence by itself is
> > sufficiently convincing to the experts that, until contradictory
> > direct evidence is discovered, they will use what they have, plus
> > informed speculation, to establish an explanation.
>
> See my comments above. Is this the way you want to present Darwinism
> in the textbooks?
>
This is exactly how science is done; why shouldn't it be taught in textbooks?
Am I claiming, as you seem to imply, that we do not need to do experiments?
No, I am not. But if science had to wait until every possible option had
been tested before proclaiming a principle as fact, we would still be living
naked in caves, freezing and starving to death because we had not yet proven
beyond all doubt that wearing skins, using fire and eating meat would benefit
us. Science advances because it takes what we know now and presents as
"facts" conclusions based on this knowledge and crafted with
deductive/inductive reasoning along with informed speculation, then uses
those "facts" as a basis for more empirical investigation. Often times the
"facts" turn out to be wrong, but more often than not this is determined
because treating them as facts leads to erroneous results that must then be
corrected, not because someone doubted the "facts" and tried to invalidate
them with tests.
Like any theory, the natural selection based on selective bird predation
conclusion should be tested, but as long as the evidence that supports it is
sound and there is no contradictory evidence, there is no reason why it
cannot be presented as "fact", provided it is presented properly.
>
> > > 4. Majerus's view is that significant bird predation levels are
> > > "highly probable" - but this is based on the consensus that bird
> > > predation is important in many species. Majerus points to the
> > > lack of data relating to the Peppered Moth.
> >
> > But this lack of specific evidence in the case of the peppered moth
> > is not enough to cause Majerus to doubt the overwhelming evidence
> > establishing the general trend that birds are the most important
> > predator as far as industrial melanism is concerned. That is
> > what we need to keep in mind. The question is, what causes
> > industrial melanism in moths? The evidence we have so far
> > indicates that it is selective predation by visually-oriented
> > predators. Of the three major groups of vertebrate predators of
> > moths -- bats and other mammalian insectivores, birds and
> > reptiles/amphibians -- only the latter two hunt predominatly by
> > sight, so only the latter two are likely to cause industrial
> > melanism. And since birds are far more numerous and far more
> > active hunters than reptiles/amphibians, birds are the best candidates
to
> > be the predator that causes industrial melanism. As such, only if birds
took
> > a tiny fraction of all moths eaten by all predators would bird selective
> > predation have no significant affect, and this is very much not the
case;
> > they rival bats as far as total intake is concerned.
>
> I repeat: is this how it is to be presented in the textbooks? This
> is not the way I want to teach science.
>
I hope you are not suggesting that deductive reasoning is foreign to science,
even when it is based on empirical evidence, though I can understand why you
might: teaching science by denying deductive reasoning would make it easier
for you to fool kids into uncritically accepting creationism/ID theory..
>
> This is not to say you are necessarily mistaken in your comments: but
> we do not have the empirical data to even test alternative hypotheses.
>
I disagree. In my opinion the evidence presented in Majerus' book and the
papers he cites can allow one to rule out the vast majority of alternative
hypotheses. The only questions left concern figuring out the exact details
of the mechanism, but it seems to me that there is little doubt over the
basic form of this mechanism: natural selection by selective bird predation.
To treat this lack of details as a serious problem for the validity of the
mechanism is in my opinion tantamount to willful blindness.
>
> > .. .. In point of fact, the
> > evidence we do have paints a very strong picture in favor of selective
> > predation by birds as the cause of industrial melanism.
>
> This may be the case, but I shall not be surprised if the story turns
> out to be wrong. But this is not the key point: which is whether the
> PM story is sufficiently robust to be the classic example of natural
> selection changing gene frequencies in a population of organisms.
>
Unable to prove it to be bogus or fraudulent, the only tactic left is to
declare it to be irrelevant simply because there are still some unanswered
questions. Except for the fact that the peppered moth scenario has been
targeted for elimination by ID political activists and you wish to toe the
party line, I would advise you not to waste your time on such a shallow,
insubstantial argument. Robust or not, it is still the most valid
explanation for industrial melanism. As such, it should be taught as fact
until evidence appears to refute it. That is how science works.
Kevin L. O'Brien