Re: [asa] New fruit fly threat in Southern California

One of David's examples below provides another example of how evolutionary
theorizing can *look* as if it contributes substantially to biological
theory or practice while *in fact* being merely a redundant interpretive
gloss.

David suggests that if we don't know much about the fruit fly in question,
we should turn to a close relative of the fly (where by close relative he
means closely related in evolutionary terms) for which we have better
information about pheromones, etc. The structure of David's argument is as
follows:

1. In order to find out how to control Fly A (about which we know little)
via a pheromone technique, we should apply our knowledge of the pheromones
of a closely related fly (about which we know much more).
2. Evolutionary theory tells us that Fly B is closely related to Fly A.
3. Therefore, Fly B is a likely source of information about the pheromones
which could help us to control fly A.

It sounds logical. But wait: how did we determine that another species was
"close in evolutionary terms" in the first place? Either we determined that
by similarities in bodily form (morphology) or by similarities of some other
kind (perhaps similarities in physiology, behaviour, or genetic make-up); or
perhaps we determined it by a combination of similarities, e.g.,
morphological plus genetic. This raises the question whether our
*historical inference* (even if it is an *entirely correct* historical
inference) that Fly B is "close in evolutionary terms" adds anything at all
to our diagnosis and prescription. I contend that it does not, and that the
"evolutionary" step is redundant, a mere interpretive gloss. In order to
show this, let me write out all the steps in David's argument, including the
implied as well as the stated ones:

1. In order to find out how to control Fly A (about which we know little)
via a pheromone technique, we should apply our knowledge of the pheromones
of a closely related fly (about which we know much more).
2. Fly B, which we know very well, has a lot of morphological,
physiological, genetic, etc. similarities to Fly A.
3. Therefore, via the theory of evolution, Fly B is a close relative of Fly
A.
4. Because they are closely related in evolutionary terms, Fly A and Fly B
will have a lot of morphological, physiological, genetic, etc. similarities.
5. Therefore, Fly B is a likely source of information about the pheromones
which could help us to control fly A.

The redundancy of Steps 3 and 4 should be obvious, but if it isn't, it can
be seen from another angle if we write out the argument as follows:

1. In order to find out how to control Fly A (about which we know little)
via a pheromone technique, we should apply our knowledge of the pheromones
of a closely related fly (about which we know much more).
2. By a "closely related fly", we understand a fly with very similar form
and/or physiology and/or genetic make-up, and by these criteria, Fly B is
closely related to Fly A.
3. Therefore, Fly B is a likely source of information about the pheromones
which could help us to control fly A.

Note that in the revised argument, all evolutionary language has been
dropped ("closely related" being defined to mean "strongly similar in key
relevant respects" rather than to imply any actual historical relationship).
Yet, despite the dropping of all evolutionary language, the analysis and
prescription of the problem *is exactly the same*. That is: "Find a fly
whose characteristics you know very well that's a heck of a lot like the fly
that's bothering you; there's a good chance that the two will have similar
pheromones."

A six-day literalist would thus come up with the same analysis and
recommendation regarding the pheromone technique. ("If God made these two
flies so very similar in so many ways, he probably gave them similar
pheromones.") Why, then, do we need to know whether the two species are
similar because they are close historical relations or because God used very
similar engineering designs in their special creation? What practical
difference does it make to the analysis and solution of the agricultural
problem at hand?

I am not concluding from this that six-day literalism is true, and that
historical evolutionary relationships are false. I am not even concluding
that six-day literalism is as plausible a theory as evolution. I am merely
making the point that, *with regard to the biological problem set forth in
the example we are discussing*, the statement that "Fly A and Fly B are
close evolutionary relatives" is an optional gloss; we can only *know* that
they are close evolutionary relatives *if we already know* their comparative
morphology, genetics, etc. But *if we already* know their comparative
morphology, genetics, etc., then we can guess that the pheromones in both
species will be similar without the evolutionary inference.

Why reason from A to B to D back to B and then to C, when one can reason
directly from A to B to C? Why else, other than that evolutionary theorists
must slip their interpretive gloss in as often as possible, even where it is
redundant?

Cameron.

----- Original Message -----
From: "David Campbell" <pleuronaia@gmail.com>
To: "AmericanScientificAffiliation" <asa@calvin.edu>
Sent: Sunday, August 02, 2009 5:46 PM
Subject: Re: [asa] New fruit fly threat in Southern California

>> I just read the following news item. Would you kindly get all the experts
>> in evolutionary biology to solve this pending problem? However, they must
>> solve the problem as evolutionary biologists not experimental biologists.
>> <
>
> Obviously, to actually deal with the problem, you have to run the
> experiment. However, evolutionary considerations can give us good
> ideas about what could be good approaches (and bad ones).
>
> For example, reproduction is essential for an organism's success.
> Reproductive cues are therefore likely, from an evolutionary
> perspective, to be both fairly species-specific and strongly
> attractive to the species. Although testing to make sure no
> non-target species are also attracted, use of artificial pheromones to
> attract the flies is likely to be one of the best approaches; a
> similar approach is to swam the area with infertile mutant males to
> reduce the odds of successful mating. (Additionally, my
> brother-in-law can get paid to fly planes dumping out flies.)
> Evolution also helps if the details for this fly have not been studied
> (potential serious invasives not yet established in Western countries
> are often poorly known). If so, we can look at close relatives to get
> a good idea of the likely pheromones, etc. to greatly speed up the
> search for what works against this fly. Conversely, it will help
> identify what harmless local species might be most at risk as
> non-target casualties.
>
> Another possibility would be to look for resistant crops. Those would
> presumably be ones that evolved in contact with the pest species.
> (However, the problem with the fly may merely be the fact that U.S.
> consumers do not like maggots in their fruit, which would not be an
> evolutionary threat to the plant.)
>
> Another possible control method would be searching for
> predators/parasites of the pest. However, this has often been badly
> mangled in the past, causing more trouble and often not controlling
> the target pest. A control organism actually from the fly's home that
> affects them, rather than something that attacks more or less similar
> things somewhere else, would be better. Parasites are able to
> specialize much more tightly than the average predator (in part
> reflecting relative size of predator/parasite to prey), so they will
> generally be a better model. Again, evolutionary considerations help
> to know what non-target species you ought to test first.
>
> --
> Dr. David Campbell
> 425 Scientific Collections
> University of Alabama
> "I think of my happy condition, surrounded by acres of clams"
>
>
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Received on Tue Aug 4 04:46:30 2009