wmartin@brl-tgr.ARPA (Will Martin ) (09/23/85)
I ran across the following passage in a rather interesting coffee-table (big-format, lotsa pictures) book called HOW ANIMALS SEE, by Sandra Sinclair (Facts on File, 1985): Celestial Navigation Observation and experimentation in planetariums have shown that birds navigate by the stars and know their positions. 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. Other experiments with various species of night-flying birds heve replicated the reults of these experiments, some of which were conducted in exterior cages under the stars. It requires an extremely large eye to detect small points of light at great distances, and the eye of the bird is certainly big enough to perceive starlight. What is of greater interest in the experiments of Dr. Sauer is that knowledge of the stars' positions appears to be innate, like the innate attraction of young gulls to yellow and red spots. (page 97) ***End of quote*** Now, note especially the last sentence above. What came to mind as I read that was this question: "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? 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. 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?) I find this a rather large puzzle. Please comment! Will Martin UUCP/USENET: seismo!brl-bmd!wmartin or ARPA/MILNET: wmartin@almsa-1.ARPA
scott@hou2g.UUCP (Racer X) (09/26/85)
[discussion on birds using star positions
and configurations to navigate...]
This is actually quite easy to explain. The birds
(like our fearless leader Ronnie) believe in Astrology!
"To order poison in a bar would be...illogical."
Scott J. Berry
ihnp4!hou2g!scottmrh@cybvax0.UUCP (Mike Huybensz) (09/30/85)
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
friesen@psivax.UUCP (Stanley Friesen) (10/04/85)
In article <1654@brl-tgr.ARPA> wmartin@brl-tgr.ARPA (Will Martin ) writes: >***End of quote*** > >Now, note especially the last sentence above. What came to mind as I >read that was this question: "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. > >... how could the learning >of such CHANGING patterns have ever become an "innate" instinct? >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. > Well, there are a couple of fallacies here. First, *exact* navigation is unnecessary, it only needs to be good enogh to get the bird into the general vicinity where visual targeting can take over. Before the invention of inertial navigation systems long range commercial flights operated this way, the pilot *assumed* he would be a little off and need to correct course on the basis of surface landmarks. Also the birds don't really need to get to an exact location(unless they are headed for a small island), they merely need to end up *together*(more or less) somewhere. Also mutational changes would likely be *quite* small and would make little difference in most situations. Thus star pattern changes would have the effect of shifting the birds' destination area slowly in some direction. Only if there is no suitable habitat in the direction of drift would there be any selection for change. In that case, however, the selection would only effect the individuals most extreme in the direction of the inappropriate habitat, removing them and leaving the others alone. Such light selection would be sufficient to adjust the map without excessive mortality destroying the species. >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?) > Well, a 200,000 yr old map might well be adequate for the birds' purposes, which is mainly to arrive at a suitable habitat with reasonable reliability in close enough proximity to others of the species to be able to mate successfully(See above). Furthermore, only the most extreme proponents of PE deny the existence of gradualistic changes, so both "rapid" and gradual shifts are possible. Actually, there have been instances of "pseudo-Lamarkian" evolution occuring. That is genetic shifts occuring which "fix" environmemntally produced changes, thus producing the appearance of inheritance of acquired characters. This seems to occur because individuals which are genetically programmed to anticipate environmental impact have greater energy reserves for reproduction and survival of "disasters". The most well documented example is the existence of Sea-bluff races of certain shrubs and trees. The salt spray from the sea "prunes" off exposed branches of woody plants leaving dwarfed, sprawling variant. Inland seeds planted in such environments produce plants indistinguishable from those grown from sea-coast seeds, but when the sea-coast seeds are grown inland they retain the sea-coast growth form! Something very similar could apply to birds' navigiation systems. That is slightly off variants would be less viable under stress conditions and in the long run produce fewer offspring than the individuals that have exact mapping capability, thus simulating Lamarkian inheritance. -- Sarima (Stanley Friesen) UUCP: {ttidca|ihnp4|sdcrdcf|quad1|nrcvax|bellcore|logico}!psivax!friesen ARPA: ttidca!psivax!friesen@rand-unix.arpa