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Microevolution due to pollution can occur mainly through genetic drift bottlenecks , especially of small sized populations facing intense lethal pulses of contaminants , through mutations , increasing allelic diversity , and through natural selection , with the disappearance of the most sensitive genotypes .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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