BISTON BETULARIA

[Glenn A. Gorelick]

Scenes of European robins, in flight, actually selecting dark(mutant) forms
of Biston betularia while ignoring the nearby light(normal) forms, on
non-polluted tree trunks can be seen in the Encyclopedia Brittanica
Educational Corporation's 1960 (or 1961) film, NATURAL SELECTION.
Kettlewell's experiments were documented on film, although the experimental
set-up (constructing vegetation "blinds" for photographers and their
cameras) was, indeed, rather artificial.

Still, according to what is actually shown in the film, the light form of
the moth was certainly preferred by the birds when the moths landed on
polluted (soot-laden) trees in the forest under study.

The film shows how humans can alter selective agents and influence shifts in
gene frequencies.  His experiments were, in my own interpretation, a major
contribution to understanding natural selection as a primary force in evolution.


Glenn A. Gorelick
Dept. of Biological Sciences
Citrus College
Glendora, CA   91741  USA