Vladimir Nabokov

NABOKV-L post 0005478, Tue, 19 Sep 2000 17:33:29 -0700

Nabokov and Mimicry (fwd)
From: Kurt Johnson <belina@dellnet.com>

For sometime now, a lingering question among Nabophiles (both on
Nabokov-on-line and at the NYTimes.com Nabokov Forum) has been "what does
modern genetics say about how exact the mimic in mimicry can become? does
a scientific explanation account for this? and what of Nabokov's noting
that perhaps some mimicry in nature was so exact as to defy a mechanistic
explanation? Current genetics' "take" on this has been one of the loose
ends in Nabokov's Blues and Nabokov's Butterflies discussions. The
matter also came up in my last personal discussion with the moderator of
this forum, D. Barton Johnson.

I decided to ask the question to a Nabokov-literate geneticist. This
answer is from Dr. James Mallet, a professor at the University of
London. Jim is not only an expert in mimicry genetics (specializing in
mimicry in Heliconian butterflies ["Longwings"]) but recently reviewed
Nabokov's Butterflies in the prestigious scientific journal
NATURE. Here is his answer to the above questions.

Dear Kurt,

Well, I am not so much of an expert on Nabokov, but I suppose I might be
classed as an expert on mimicry genetics.

1) From the 1960s onwards, an enormous literature on the evolution and
genetics of mimicry has appeared. The major conclusion of evolutionary
biologists is: yes, natural selection can and does explain the evolution of
mimicry. Nobody today seriously disagrees, and my own view certainly
conforms with this.

a) To my knowledge, no mimicry gene has yet been sequenced and
characterised at the DNA level (work is ongoing at the moment), but
Nijhout's book as well as many other publications provide evidence that
normal genetic mechanisms are at work to produce mimetic adaptations.

b) Natural selection on mimicry of warningly coloured butterflies has been
studied in the field, and it has been shown that predator selection
pressures can be very intense. I did one such experiment myself: the
butterflies with the wrong colour pattern had half the lifespan of the
butterflies with the mimetic pattern. This provides a powerful force of
natural selection for mimicry!

c) Of course, experiments like these are usually done on extremely
different mimics and non-mimics (otherwise, the effect would be weak, and
experiments would require impossibly huge sample sizes). The experiments
therefore do not specifically answer the question about perfection.
Obviously, perfect mimicry is likely to be only a little advantageous over
fairly good mimicry. Very likely we wouldn't be able to measure the benefit
of mimetic perfection in experiments with even a few hundred predators and
prey. But given that major changes have very major fitness effects, it
seems almost certain that very slight improvements will have small fitness
advantages that have appreciable effects over many thousands, and often
millions of generations. We also know now that many birds and other
predators have extremely acute vision, often more acute than our own.

d) Most of the studies have been done in palatable mimics of unpalatable
butterflies. I read somewhere that Nabokov believed that some spots on
lycaenid butterflies ("blues") mimicked drops of dew, and that the
perfection of shading of a 2-D wing spot mimicking the 3-D drop was what
triggered Nabokov's lack of belief in the power of natural selection. I
don't know the specific spots to which Nabokov was referring, but I do know
plenty of examples of 3-D eyespots on insects which are made to look like
real eyes using delicate shading. Given that colour patterns can and do
evolve, and that eyespots can be very frightening, I can well believe that
this kind of camouflage would evolve under natural selection. No work has
specifically been done on the perfection of eyespots, to my knowledge, but
eyespots and artificial models of eyespots have been shown to be very
terrifying to bird predators.

2) Something that one should always remember is that much mimicry is really
not very perfect at all, in many cases! For example, red and yellow spots
on the thorax and abdomens of poisonous pharmacophagous swallowtails in SE
Asia are mimicked by red patches at the base of the wings of their mimics,
the female forms of the swallowtail Papilio memnon. Another example is
flies mimicking wasps. Many stinging wasps fold the anterior part of their
forewings, making them look darker at the front edge. Syrphids and other
flies usually mimic this by means of darker pigment on the front margin of
the wing, rather than actually folding the wing. This LACK of perfection
of mimicry, a kind of impressionism, is exactly what one would expect if
the mimicry were cobbled together by natural selection, rather than created
by a perfect designer.

I am reminded of a PhD student who was a creationist in this Department.
He told me he believed that mimicry was too perfect to be explained by
natural selection. Although he understood and believed in natural
selection, he really felt this might be evidence for the guiding hand of
the creator. He suffered a nervous breakdown, and has never completed his
PhD. Possibly the stresses that had built up between his excellent
knowledge of evolutionary biology and his faith played a role in making
life difficult for him. Perhaps Nabokov, who produced his "mimicry too
perfect" argument as far back as in "The Gift", was perhaps not thinking
too carefully about the data when he made these claims. Maybe it is just
as well for his sanity that Nabokov never did write that book on mimicry
which he discussed with a publisher!

This is probably too long for you, but oh well!

Prof. James Mallet