In the early 1800's, peppered moths living in England rested on tree trunks that were covered with whitish lichens. The moths were also whitish in color and so matched the color of the background on which they rested. This made the moths less visible to the birds that preyed on them. In the late 1840's, an increasing number of very dark moths began to appear in moth populations near cities where pollution had killed most of the lichens, leaving the tree trunks sooty and black. Over the past 100 years, the frequency of dark moths has increased to as much as 98% in populations near polluted cities. What type of selection has operated on moths in the polluted areas since 1840? Justify your answer. mark 2
Answers
The evolution of the peppered moth is an evolutionary instance of directional colour change in the moth population as a consequence of air pollution during the Industrial Revolution. The frequency of dark-coloured moths increased at that time, an example of industrial melanism. Later, when pollution was reduced, the light-coloured form again predominated. Industrial melanism in the peppered moth was an early test of Charles Darwin's natural selection in action, and remains as a classic example in the teaching of evolution.[1][2] In 1978 Sewall Wright described it as "the clearest case in which a conspicuous evolutionary process has actually been observed."[3][4]
Biston betularia f. typica, the white-bodied peppered moth.
Biston betularia f. carbonaria, the black-bodied peppered moth.
The dark-coloured or melanic form of the peppered moth (var. carbonaria) was not known before 1811. After field collection in 1848 from Manchester, an industrial city in England, the frequency of the variety was found to have increased drastically. By the end of the 19th century it almost completely outnumbered the original light-coloured type (var. typica), with a record of 98% in 1895.[5] The evolutionary importance of the moth was only speculated upon during Darwin's lifetime. It was 14 years after Darwin's death, in 1896, that J.W. Tutt presented it as a case of natural selection.[6] Due to this, the idea widely spread, and more people believed in Darwin's theory.
Bernard Kettlewell was the first to investigate the evolutionary mechanism behind peppered moth adaptation, between 1953 and 1956. He found that a light-coloured body was an effective camouflage in a clean environment, such as in Dorset, while the dark colour was beneficial in a polluted environment like in Birmingham. This selective survival was due to birds which easily caught dark moths on clean trees, and white moths on trees darkened with soot. The story, supported by Kettlewell's experiment, became the canonical example of Darwinian evolution and evidence for natural selection used in standard textbooks.[7]
However, failure to replicate the experiment and criticism of Kettlewell's methods by Theodore David Sargent in the late 1960s led to general skepticism. When Judith Hooper's Of Moths and Men was published in 2002, Kettlewell's story was more sternly attacked, accused of fraud, and became widely disregarded. The criticism became a major argument for creationists. Michael Majerus was the principal defender. His seven-year experiment beginning in 2001, the most elaborate of its kind in population biology, the results of which were published posthumously in 2012, vindicated Kettlewell's work in great detail. This restored peppered moth evolution as "the most direct evidence", and "one of the clearest and most easily understood examples of Darwinian evolution in action".[8]
Answer:
g
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