Subject: Re: the significance of a wing bar
Date: Apr 26 17:24:16 1995
From: Christopher Hill - cehill at u.washington.edu




On Wed, 26 Apr 1995, Dennis Paulson wrote:

> Burt Guttman wrote:
>
> "Every feature of an organism does not necessarily have a function.
[snip]

Dennis Paulson responded:

[big snip]
> I don't even have a hypothesis for some of the possible
> functions, but those little markings, recurring again and again on birds of
> different origins but similar life styles--they're "good for" something!

I want to make two quick points. First, a non-adaptationist rant I mean
alternative hypothesis: I would think that the observation that the same
patterns (wing-bars, eye rings) recur on many unrelated taxa could have a
developmental origin. Maybe many groups have evolved
wing-bars because they're easy to evolve. Dennis, I know you said
"similar lifestyles," and I'll grant that some e common plumage badges
seem to be associated with particular lifestyles (e.g. yellow breast with
black "vee" in several unrelated prarie birds, white outer tail feathers
in flocking, ground feeding open country birds). But without more
evidence, I won't accept that ALL markings are adaptive.

My second example may be illustrative, though it doesn't involve birds.
Consider the gastropod (marine snail) genus _Conus_. Their shells, prized
by collectors, are wondrously patterned, with tremendous variety and
flashiness, and the shells are completely invisible while the animal is
alive, because the fleshy part of the animal covers the shell completely.
It's easy to come up with an adaptationist explanation - assume the
colorful shells are costly and look for an possible function and you have
an explanation that's almost too good. The animals are dangerous - humans
die every year from _Conus_ injected venom, for example, and the threat to
smaller animals is even greater. But the shell patterns are invisible in
life, and an examination of the mechanisms of development showed that the
shell patterns are explainable fairly easily by mechanistic (geometric?)
rules of shell deposition during development.

So when you look for meaning in the coloration of the third under
scapular retrix covert, I think you have to ask yourself "Is this just an
accident, like _Conus_ shells?"

Chris Hill
Seattle, WA
cehill at u.washington.edu