Wednesday, March 01, 2006


Retrograde Motion and Evolution

A webpage on Retrograde Motion at Philadelphia's Lasalle University states:

One phenomenon that ancient astronomers had difficulty explaining was the retrograde motion of the planets...

...a planet appears to move from West to East against the background stars most of the time...

...Occasionally, however, the planet's motion will appear to reverse direction, and the planet will, for a short time, move from East to West against the background constellations. This reversal is known as retrograde motion.

Ptolemaic Explanation

This model consisted of a series of concentric spheres, with the Earth at the center...

...To account for the observed retrograde motion of the planets, it was necessary to resort to a system of epicycles, whereby the planets moved around small circular paths that in turn moved around larger circular orbits around the Earth...

...In its final form, the model was extremely complicated, requiring many nested levels of epicycles (etc.).

Copernican Explanation

Copernicus replaced the geocentric universe of Ptolemy with one that was centered on the Sun (heliocentric), with only the Moon orbiting the Earth. His model was still based on circular orbits (and therefore still required further refinement), but it was able to achieve superior precision than the Ptolemaic model without the need for epicycles or other complications. [My emphasis]
If the proposal of an internal evolutionary mechanism is seen as a Copernican expansion upon the Ptolemaic modern synthesis, then in terms of explanatory power alone, obvious areas to zero in on would be any evolutionary equivalents to retrograde motion.

Evolutionary atavisms are among such suitable candidates and have been brought to the fore (for a day or two at least!) by John F. Fallon's kind response to a request for a copy of The Development of Archosaurian First-Generation Teeth in a Chicken Mutant.

In the near future I hope to post a brief explanation of how the proposed mechanism could account for the phenomena reported in the above paper. It won't be definitive but it should make 'operation' of the mechanism a little clearer.

Finally, the 'old' chinese proverb "A picture is worth a thousand words" (apparantly coined as "A Picture's Meaning Can Express Ten Thousand Words" as part of an ad campaign in 1927!) is clearly shown by the two animated gifs on the Lasalle webpage demonstrating the difference between the Ptolemaic and Copernican explanations of retrograde motion.

John Latter

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