Q.You have studied the story of Pepper moths in England. Had the industries been removed, what impact could it have on the moth population? Discuss.
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Start your 14-day free trial to unlock the full solution →If industries had been removed, the soot-darkened tree trunks would have lightened again, reversing the selection pressure and allowing the light-coloured peppered moths to regain their advantage over the dark melanic forms.
The peppered moth story is one of the most elegant demonstrations of natural selection in action, observed in real time during the Industrial Revolution in England. Before industrialisation, the typical peppered moth had light-coloured, speckled wings that blended beautifully against lichen-covered tree bark. This camouflage protected them from predatory birds. The dark melanic variety existed but was rare, because on pale lichen it stood out and was quickly spotted and eaten.
When coal-burning industries spread across England in the nineteenth century, soot blackened the tree trunks and killed the lichen. Suddenly the environment had changed. The light moths, once invisible, became conspicuous against the dark bark. The dark moths, previously at a disadvantage, now had the better camouflage. Birds preferentially ate the light moths, and over a few decades the dark form became overwhelmingly common in industrial areas. This shift in the population was directional selection driven by predation pressure in a polluted environment.
Now imagine the industries had been shut down or relocated. The air would have cleared, soot deposits would have washed away with rain, and crucially, lichen would have recolonised the tree trunks. The bark would have returned to its original pale, mottled appearance. In this restored environment, the selection pressure would reverse entirely.
The dark moths, which had thrived in the industrial landscape, would once again become visible targets. Birds would hunt them more successfully than the light moths. Generation by generation, the frequency of the melanic allele would decline as fewer dark moths survived to reproduce. The light-coloured moths, now camouflaged once more, would leave more offspring. The population would shift back toward the original light phenotype.
This is not the moths "choosing" to change or individuals transforming. The genetic variation for both colours already exists in the population. Selection simply changes which variants survive and reproduce more successfully. …
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