D'Abrera on Science and Philosophy

[Doug Yanega]

John Grehan wrote:

>Returning to butterfly mimics, resemblance may well be the coincidental
>result of similar evolutionary trends in different species.

Let me put it this way: both you and D'Abrera are at the very least
suggesting that these matching color patterns are arising as independent
events. If you do not invoke selection, what possible explanation can you
offer for the fact that each and every case of highly correlated coloration
occurs ONLY in sympatric taxa? What explanation do you offer for the
numerous Lepidoptera which mimic insects in other groups, especially bees
and wasps, and why is it ONLY taxa like bees and wasps, and not harmless
insects like termites and roaches and beetles and flies that they resemble?
After all, if variation is infinite, then there should be some members of
every insect group that look like some members of every other insect group,
no??
        Moreover, mimicry complexes commonly include members of taxa which
do NOT normally bear any resemblance whatsoever to the taxon they are
mimicking - in other words, the mimetic species are clearly NOT the result
of evolutionary trends within that group, but rather a huge leap with no
intermediates (for example, there are a few genera of bee/wasp-mimicking
leafhoppers and katydids, a far stretch for either of those taxa), or at
the very least cannot be said to be experiencing similar evolutionary
pressures that might lead them to have similar appearances. Give me one
good reason, for instance, why a whole pile of small parasitic wasps,
beetles, and hemipterans should be experiencing pressure to develop
markings that create the impression of ant-like abdominal petioles (in
combination with ant-like antennal morphology, ant-like body movements, and
general ant-like coloration), if it is NOT pressure specifically to
resemble ants. These are not cases of just random variation; these are
pronounced deviations from the normal appearance of members of the group,
all the parts of which are converging on a very specific and sympatric
model, for which the ONLY reasonable explanation is that they were selected
for.
        By restricting your concept of mimicry solely to similar patterns
on wings between Lepidopterans, you are restricting yourself to one of the
weaker lines of evidence for mimicry as a real phenomenon. There's a lot
more to it.

>With
>development of this similarity (either within closely or distantly related
>species) comes selective interactions that are also going to affect the
>process, but selection is not required at the outset as a necessary causal
>agency.

Maybe I'm taking your comments too literally, but no one ever suggested
that selection *causes* mimetic mutations to occur to start the process.
Selection is not what is required at the outset, but rather any mutation
that leads to similarity, which is an essentially random process. Then come
the selective interactions, as you acknowledge. That's really all there is
to it - it boggles the mind that D'Abrera could see this as a great failing
for evolutionary theory.

Peace,

Doug Yanega    Depto. de Biologia Geral, Instituto de Ciencias Biologicas,
Univ. Fed. de Minas Gerais, Cx.P. 486, 30.161-970 Belo Horizonte, MG   BRAZIL
phone: 031-449-2579, fax: 031-441-5481  (from U.S., prefix 011-55)
                  http://www.icb.ufmg.br/~dyanega/
  "There are some enterprises in which a careful disorderliness
        is the true method" - Herman Melville, Moby Dick, Chap. 82