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Fw: Alexander agrees with Zimmer
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----- Original Message -----
From: Victoria N. Alexander
To: Vladimir Nabokov Forum
Sent: Monday, September 02, 2002 8:37 AM
Subject: Re: Alexander agrees with Zimmer
The question about mimetic forms concerns how they arise. Do they arise gradually, through natural selection? or do they arise suddenly, by chance?(and then, perhaps, get selected). If mimetic forms arise suddenly by chance and are not shaped gradually by natural selection, then we will want to try to understand the mechanics behind the formation of these patterns and understand why they might be probable. The preferred approach to this question these days is through physics. The desire is to try to understand the laws of pattern formation. If computer simulations of reaction diffusion processes can produce "eye-spots" and viceroy-monarch patterns spontaneously (without the help of predators or natural selection) then there is no need to posit additional explanations (e.g. function) for the existence of these patterns.
Although it might be theoretically possible to observe the evolution of mimetic forms by observing predators and butterflies engaged in a feedback relationship for many generations, it is practically impossible. (A number of human cultures might rise and fall during the time necessary to observe these changes.) The only confirmed observations of adaptation that I know of are the studies on bacteria that I have already mentioned (they are sufficiently simple and replication times sufficiently rapid) and moth populations in England that adapted darker camouflage coloring in response to the soot-stained bark in certain industrial regions. (In my talk at St. Petersburg I explain why camouflage is fairly easy for natural selection to find, while a mimetic form is not. This was Nabokov's argument. That talk will be available online soon.) The numerous studies attempting to measure the abilities of predators to interpret shapes are, in my opinion, inconclusive. Some try to argue that predators are careless and might think any pair of spots are eye-like, thereby initiating the unlikely adaptation of owl's eye spots on butterfly wings; other studies try to argue that predators are especially keen and are only fooled by very eye-like spots, thereby fine tuning the mimetic representations of owl's eyes on butterfly wings. Since computer simulations have shown that "eye-spots" occur spontaneously and frequently without any kind of selection pressure, these studies become superfluous to understanding why "eye-spots" exist. Similar arguments can be made for the viceroy-monarch relation and even the dead leaf mimic.
My argument agrees more or less with Dieter Zimmer's findings. The only significant differences lies in my lack of interest in the studies of predator/prey behaviors. I generally don't find field studies very reliable since they involve so much subjectivity on the part of the scientists and are also insufficient in terms of time scales. I much prefer the approach of theoretical biologists.
Tori Alexander
On Sunday, September 1, 2002, at 02:20 PM, D. Barton Johnson wrote:
----- Original Message -----
From: Dieter E. Zimmer
To: Vladimir Nabokov Forum
Sent: Sunday, September 01, 2002 12:01 AM
Subject: Re: Alexander replies to Dieter Zimmer on Darwin
Yes, Nabokov at times willingly conceded that mimetic phenomena do afford protection, not only in his 1949 paper on Lycaeides Ms. Alexander cites. Even in the passage that is always quoted ("Gift" p.110) he writes that "the incredible artistic wit of mimetic disguise [...] was too refined for the mere [!] deceiving of accidental predators..." That is, he did not at all deny that mimicry was useful as a protective device. His argument was that there was a special quality to some mimetic phenomena that could not be explained by its usefulness and hence by natural selection ("the struggle for existence"). This additional quality he saw in a kind of aesthetic surplus: some cases of mimicry, he thought, are too refined for the discriminative powers of the predators--these cannot really appreciate the perfection of the thing. Now this is not philosophy of nature but sound science, for it is a testable hypothesis that can be either confirmed or falsified. It could not be done in a general way--each instance would have to be examined. To my knowledge there has not been a single instance so far proving that, yes, less perfect mimicry would afford just the same protection. Predation usually does not happen in an atmosphere of leisure where a predator can quietly contemplate and appreciate the degree of perfection in his potential prey. He has to decide quickly whether he wants to risk taking a pick at a lep that is in movement and only partly visible to him. So even a very imperfect mimic might enjoy some protection, benefiting from a moment of doubt as to its palatability. This, however, does not exclude that a more perfect mimic might enjoy more protection. It is not an all-or-nothing affair as Ms. Alexander seems to suggest. Still there actually might be cases of aesthetic surplus in mimicry, and as I argued in my 1999 paper they might be explainable by genetic drift (neutral evolution) or structural constraints (structural evolution). The important thing to realize is that neutral or structural evolution, if they can be shown to have produced a certain case of mimicry, would not have happened in place of natural selection but just supplemented it.
All of this underscores my point that Nabokov was not irreconcilably far removed from the theory of natural selection and might after all have adjusted his thinking to it if the evidence had pointed that way.
Dieter E. Zimmer
Berlin, September 1, 2002
mail@d-e-zimmer.de