Tuesday, June 17, 2003

Peppered Mice? From The New York Times comes this article about
Rock Pocket Mice in the American Southwest. Most of these mice sport a sandy beige color, perfect for camouflaging themselves against a desrt background.
But in certain areas, ancient lava flows have darkened the ground to a point where the mice are far more visible to predators, especially owls. In these areas a dark form of the mouse has evolved.

This case parallels that of the peppered moth, in which a dark form of the normally light-colored moth evolved in response to industrial pollution that darkened the trees on which the moths reside. Creationists have seized on the peppered moth example, pointing out that more recent research has suggested that the adaptive signifcance of dark coloration may be more complicated than mere camouflage from predators. In their telling this constitutes some great scandal.

Anyway, the present example is especially significant for two further reasons. The first is that the selection pressures to which the mice were responding were entirely natural. In this they differ from several other notable cases of rapid evolutionary change. For example, the pollution to which the moths responded was man-made, as were the pesticides to which certain strains of fruit flies developed resistance. The second reason is that geneticists were able to identify the precise genes responsible for the color change.

Perhaps the mice will become a new textbook example of evolution in action.


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