Rapid change in phenotype doesn't necessarily imply an increased mutation rate. Rather, new and strong selection pressure can be working on existing variation.
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I would tend to to agree with you. But it could also mean that changes originated from neural system may be intervening. (see
http://www.sleepgadgedabs.com). Your use of the word "rather" i suppose you imply that you accept the possibility, that other things could be happening as well.If strong selection pressures is the only couse, which might well be true, then it has to clearly beyond any doupt be proved; and particularly it has to be sure that other co-working couses are excluded.
Edited by zi ko, : No reason given.