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From: cjm@reed.UUCP (Chris Marshall)
Newsgroups: sci.bio,talk.origins
Subject: Re: The birds and the beaks
Keywords: evolution, birds, beaks
Message-ID: <12326@reed.UUCP>
Date: 7 Apr 89 01:17:20 GMT
References: <404@censor.UUCP> <27216@apple.Apple.COM> <464@corpane.UUCP> <28426@apple.Apple.COM>
Organization: Reed College, Portland OR
Lines: 68



Bryan, I've been following your discussion for a week or so and have had a 
problem with the question you are addressing.  The original question of
"why do birds have beaks? which is analogous to many other questions 
regarding a variety of character traits in an array of organism such as 
you pointed out with your giraffe example of "why do giraffes have long
necks".  The problem with these sorts of questions is that the question is
not clear enough.  Are you refering to what evolutionary issues caused
beaks to become prevalent in birds, or are you discussing what current
environmental cirumstances exist such that beaks are a favorable trait?

the two question are quite different, and have I think resulted in the 
general dismay that other readers have voiced concerning the discussion
in general.  Is it truely possible to show that beaks are an adaptive
trait which arose due to specific selective forces favoring them; 
specifically flight?  An example of what I'm trying to say can be seen
in the case of artic animals such as the arctic fox.

In looking at the arctic fox one notes that its ears are much smaller than
its more temperate cousins.  From this one might be led to the question of
why do arctic foxes have small ears?  Once doing so, the investigator can
then proceed to make observations, do experiments and such in order to 
examine the roll of the smaller ears within the arctic environment.  He/She
may come to the conclusion that the small ears grant the fox an advantage in
cold environments because of reduced heat loss.  So, then is it correct to
assume that small ears arose over evolutionary time because of natural 
selection's favoring of small ears in foxes?  The answer is no.  This does
not necessarily follow as the small ears could have arisen for a variety of
non-adaptive factors and was subsequently maintained in the population because
of the proximate effects of the environment.  However, all is not lost, for
studies investigating ear size in other organisms also show that reduced ear
size is correlated to colder conditions (arctic rabbits and wolves show a
similar phenomenon).  This tends to give more support to the claim that 
small ears are an adaptive trait, but still doesn't prove it.  The question
then arises as to how much evidence needs to be given in order to show that
a trait is adaptive?  

Obviously your disscussion has shown that very little evidence indeed needs
to be given in order to "prove" the adaptive nature of beaks for many 
people.  In fact many people are happy to accept just about any adaptationist
story about any organism, including humans.  Thus, we have a large mass of
fun nature stories concerning "why this" and "why that".  I am not, I have
to state, undermining adaptation as a fundamental evolutionary process,
however, I think that under many cases, such as birds and beaks, it is
not possible to provide the answer.  As in the above case of ears, there
are a vast array of organisms which live in both cold and warm environments.
Such comparisons are not as easy in your case, comparison to bats is close
to this, but there just isn't enough other animals to compare with.

The other approach which would be analogous to comparing all the animals
with small ears to check for environmental similarities...such as your 
comparison to parrot fish and turtles are equally unconvincing.

A good article to read would be Gould and Vrba (1982) "Exaption--a missing
term in the science of form", Paleobiology, 8(1):pp4-15.  It goes through
this issue as well.   

I wish you luck in finding out the definitive answer to your question...but
   in truth I think it will ultimately depend on what you consider to be
   "definitive". Maybe a better question would be: "Why are humans so 
   obsessed with the question of why birds have beaks?"

   please respond via mail- (I tried to mail this letter to you but somehow
   it bounced back)

   -chris marshall