D'Abrera on Science and Philosophy

[John Grehan]

>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?

I look at the origin of resemblance as possibly being coincidental,
although this
is, I realize, a tricky work as where mimicry occurs in groups that are
relatively
closely related in which case its not so much coincidence as similar trends
against a background of common ancestry. I do not preclude selective processes
affecting the process. If mimicry were a simple matter of a single
character difference
perhaps selection is all that is necessary. Where a combination of
characteristics are
involved I am less inclined to see it purely in terms of selection, but
rather selection
working on what is already developed.

As for what possible explanation I can offer, I would first like to know
that nature
of the question. If you have already decided that selection is all that
there is to it you
will only reject the alternative as untenable, unconvincing etc (perhaps
not, but that's
the general tenor of responses when questions like this are involved).

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?

Again, I have no problem with selection being involved, and perhaps I did not
word myself clearly on that, but as for the initial resemblance there is
the problem
of not being able to select what is not already present.


>After all, if variation is infinite,

I don' know that it is, and I doubt that it is.

then there should be some members of
>every insect group that look like some members of every other insect group,
>no??

Since I do not consider variation as infinite I would say 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.

I agree with this observation. I do not see it as a problem for my perspective.

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.

Why should there be any "pressure" involved in the development of these
characteristics?
Once there is a coincidence of sufficient form (including behavior),
spatial interaction
etc., I see scope for selective processes in the subsequent shift in
improbable patterns
of variation.

These are not cases of just random variation;

I agree

 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.

I see other explanations, but whether they are "reasonable" seems to be a
political judgement. I don't know the politics of nature.

>        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.

Agreed. Sorry if I wrote to suggest this.
>
>>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.

I guess this is where we differ. You see mutations as entirely random (I presume
that you would see evolution as hardly occuring at all if it were not for
selection). I
see mutations occuring in a non-random way, with both constraints on the
types of mutations that may occur, and the way in which mutations may spread
through the popultion without selective elimination of individuals.

 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