Burt Guttman wrote:

"Let me make an important point that I've made on Tweeters before: Every
feature of an organism does not necessarily have a function. It's easy
to look at a crest on the head or a spot on the wing and ask, "What's
that good for?" The answer may be, "Nuthin!" It just happened. This
population happened to get the genes for long feathers on the head or a
white spot on the wing, and nothing in their lives selected _against_ it,
so there it is, for all to enjoy. Maybe it becomes one of the little
signals that individuals use for finding mates or something like that,
but not necessarily. Every function has to have a form, but not every
form has a function. (General biology lesson for the day, courtesy of
your friendly neighborhood state employee. No charge.)"

Oh boy, Burt, you've got this particular adaptationist excited now. Tell
me that Ruby-crowned Kinglets evolved an eye ring and Golden-crowned
Kinglets an eye line just by genetic accident, or that half the vireos and
warblers have wing bars and half don't just by genetic accident. Or that
some sparrows have white outer tail feathers and some don't, again for no
particular reason. 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!
It costs--biochemically--to make the longer feathers of a crest. My
working hypothesis is that the crest would indeed be selected against if it
were of no significance to the bird.

I sit here in the museum examining gull wings and shorebird scapular
markings and sparrow patterns, and I go home and look at red dragonflies
and blue dragonflies, and I can't reach any other conclusion but that the
differences mean something. If I were more efficient and productive, I'd
be turning out one paper after another about the adaptive significance of
various aspects of animal coloration.

My general biology lesson of the day is "there's a whole lot out there we
don't understand."

Dennis Paulson, Director phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416