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THE PEPPERED MOTH
BISTON BETULARIA BETULARIA
CARBONARIA
Natural selection
Microevolution: change in allele frequency in a population
 Industrial
Revolution caused tree
trunks to be black from soot
 By 1895, 98% of population of
Peppered Moths near Manchester were
black
 Differential bird predation is thought to
be the agent responsible
 1950s: Kettlewell’s predation and
mark/release/recapture experiments
gave positive results.
Following anti-pollution laws, carbonaria (the
black variety) began to decline on both sides of
the Atlantic
 This was because the tree trunks were now paler
and the black moth was easier to see
 The pale moth numbers now increased
 The agent of natural selection was the colour of
the tree bark
 As this changed from white to black and back
again, the black and white varieties became
more or less obvious.

BIOLOGICAL EVOLUTION
 Defined
as changes in heritable
material (i.e. genes) through time.
 Changes
in the frequency of the
carbonaria gene provides irrefutable
proof of biological evolution
KETTLEWELL’S BARREL EXPERIMENTS
Black
f. betularia
f. carbonaria
Totals
20
38
58
39
21
60
59
59
118
background
White
background
Totals