Evolution__3rd_Edition

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Figure 5.4
Peppered moths naturally settle on the undersides of twigs
in higher branches of trees (and not on tree trunks, as is
sometimes said). Melanic forms are better camouflaged in
polluted areas: compare (a) the peppered form and (b) the
CHAPTER 5 / The Theory of Natural Selection 109
melanic form, both photographed in a polluted area. (c) and
(d) show that peppered forms are well camouflaged in
unpolluted areas. Reprinted, by permission of the publisher,
from Brakefield (1987).
is uncertain, and it may have differed from the dominance shown by the melanic alleles
that exist in modern populations.
The first estimates of fitnesses were made by Haldane (1924), and he dealt with the
problem of varying degrees of dominance by making two estimates of fitness, one
assuming that the C allele is dominant and the other assuming that the heterozygote
is intermediate. The real average degree of dominance was probably between the two.
Here we shall look only at the estimate for a dominant C gene.
5.7.2 One estimate of the fitnesses is made using the rate of
change in gene frequencies
What were the relative fitnesses of the genes controlling the melanic and light coloration
during the phase from the early nineteenth to the mid-twentieth centuries, while
the melanic form increased in frequency in polluted areas? For the first method we need