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>>One question this debate does raise... is there such a thing as genetic
>        Personally, I do not know. I believe the topic was discussed in a
>class I had a while back, but I've been too busy with geology to spend much
>time with biology in the recent past.

Actually, there are a handful of well-documented cases of true reversal.
One of the best is a very derived hylid frog with full lower dentition.  No
other frog has lower teeth.  Either lower teeth were lost hundreds of times
independently, or they were regained in this particular lineage.  I don't
know if the specific genetic basis for this has been identified, but the
switching off of a regulatory gene is reasonable.


Christopher Brochu

Postdoctoral Research Scientist
Department of Geology
Field Museum of Natural History
Lake Shore Drive at Roosevelt Road
Chicago, IL  60605  USA

phone:  312-922-9410, ext. 469
fax:  312-922-9566