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From: mrh@cybvax0.UUCP (Mike Huybensz)
Newsgroups: net.bio,net.origins,net.rec.birds
Subject: Re: Evolution of vision-based instincts
Message-ID: <777@cybvax0.UUCP>
Date: Mon, 30-Sep-85 16:08:35 EDT
Article-I.D.: cybvax0.777
Posted: Mon Sep 30 16:08:35 1985
Date-Received: Wed, 2-Oct-85 20:35:26 EDT
References: <1654@brl-tgr.ARPA>
Reply-To: mrh@cybvax0.UUCP (Mike Huybensz)
Distribution: net
Organization: Cybermation, Inc., Cambridge, MA
Lines: 66
Xref: linus net.bio:142 net.origins:2416 net.rec.birds:218
Summary: 

In article <1654@brl-tgr.ARPA> wmartin@brl-tgr.ARPA (Will Martin ) writes:
> HOW ANIMALS SEE, by Sandra Sinclair (Facts on File, 1985):
> Dr. Sauer of Freiburg
> University raised night-migrating warblers in confinement, then took them 
> to a planetarium with projected replicas of the major stars. The baby
> birds adjusted their position to the direction in which the parents were
> already flying. When he changed the positions of the stars, the birds
> readjusted themselves.
> ...knowledge of the stars' positions appears to be innate.... (page 97)
> 
> How could such an innate ability, or
> 'instinct', evolve?  Especially since the position of the stars
> CHANGES over the millenia -- far too slowly to be visible, but 
> the pattern(s) of stars in the sky (which presumably is what the
> birds are comparing with 'internal templates' to navigate) is not
> the same 100,000 years, or a million years, ago.
> If "Lamarckism" or the inheritance of acquired characteristics, is
> a false concept (as we have been taught), how could the learning
> of such CHANGING patterns have ever become an "innate" instinct?

Looking at the question from the narrow viewpoint of "how is there enough
time?", the answer would need to be that evolution proceeds faster than the
sensory cues change.  Population biology shows that a thousand generations
is frequently enough to drive a slightly more adaptive gene to prominance
in a polutlation.  For birds with an annual life-cycle, this would be far
faster than the constellations change.

> You can postulate the usual random evolutionary methods making
> some birds survive because they had a randomly-generated internal
> star map installed by mutation that happened to match more accurately
> the real night sky, and the others, who got mutated to have wrong
> internal star maps, flew out to sea and died, but I would think that
> such a mechanism would result in most of the species dying off
> fairly quickly.

Migration probably didn't start out *poof* as multi-thousand mile jaunts
guided by internal star maps (and other cues.)  Cues for orientation such
as star maps might even have predated lengthy migrations, and been used
for local navigation at night.  Migration may have started as a small
annual jaunt (say between nearby areas of different elevations, or nearby
seasonal food resources) that gradually got larger (either because of
changing conditions, or because individuals who were able to migrate
farther were able to outcompete others because of access to new resources.)

> Also, the newer concepts of "punctuationalism", or brief spurts of
> frantic evolutionary change, doesn't work well here -- suppose
> that change-spurt happened 200,000 years ago. The birds would then
> have 200,000-year-old star maps genetically encoded, and would
> either have to have gradual evolution changing those maps over
> the intervening years, or have all navigated wrong beginning whenever the
> star positions have changed enough to invalidate their genetic 
> encoded charts. (And how would such gradualism have occurred over the
> intervening years without Lamarck-like processes driving it?)

Nobody has much idea whether puntuationalism would apply to non-morphological
features such as star maps or behavior.  Gradualism might well be fast enough
to account for changing star maps.  (Star maps may not really need to change
very quickly either, since only nearby stars, which aren't the brightest, seem
to move rapidly.)  It's probable that the earthly resources that birds
navigate to change location much more rapidly than the stars move.  Marshes,
swamps, lakes, islands, rivers, etc. are evanescent on the geological time
scale.  Think of all the islands and shorelines submerged since the last
melting of the glaciers abotu 10,000 years ago.
-- 

Mike Huybensz		...decvax!genrad!mit-eddie!cybvax0!mrh


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