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Natural selection at work http://www.techapps.net/interactives/pepperMoths.swf Variation occurs The new feature / characteristic now dominates the former. Increase in population ‘Fittest’ survive and reproduce Original allele frequency reduced The new allele frequency increases Their gene/allele frequency remains high This variant survives and reproduces Environmental change occurs A different variant is now better suited In natural selection, some of the population may die as a result of a change in the environment, whatever the selective agent is. Those that survive, adapt to the new environmental change because of beneficial mutations that allowed them to tolerate the new change. These mutated genes will be passed on to next generations. Two examples are peppered moth and mosquitoes. Peppered moth: in a heavily industrialized regions, moth colour changed from white to brown. A selective agent such as a bird can easily spot them against the white lichen covering the trees. But when peppered moth cover a tree trunk that has been blackened due to chemical pollution, then it is selected to adapt to the new change in the environment.