Peppered Moth-Evolution in Action

Natural selection is the process by which
favorable heritable traits become more
common in successive generations of a
population of reproducing organisms, and
unfavorable heritable traits become less
common.

Natural selection acts on the phenotype, or
the observable characteristics of an organism,
such that individuals with favorable
phenotypes are more likely to survive and
reproduce than those with less favorable
phenotypes.

Charles Darwin accumulated a tremendous
collection of facts to support the theory of
evolution by natural selection.

One of his difficulties in demonstrating the
theory, however, was the lack of an example
of evolution over a short period of time,
which could be observed as it was taking
place in nature.

Although Darwin was unaware of it,
remarkable examples of evolution, which
might have helped to persuade people of his
theory, were in the countryside of his native
England.


One such example is the evolution of the
peppered moth Biston betularia.
British ecologist H. B. D. Kettlewell.


The economic changes known as the
industrial revolution began in the middle of
the eighteenth century.
Since then, tons of soot have been deposited
on the country side around industrial areas.


The soot discolored and generally darkened
the surfaces of trees and rocks.
In 1848, a dark-colored moth was first
recorded.

In 1950 man interceded again with the
passage of smoke control laws in England
and the land once again began to be green
once again.


During 1966- 1969, a survey of the town
showed that of the 972 specimens collected,
25 were of the light speckled variety.
This is a clear indication that the peppered
moth is again in the process of changing its
color once again.