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Theories of evolution

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Evidence for evolution: rapid changes

Mutationsmutation: An error in DNA replication which results in a change in an organism's genetic blueprint. Some mutations are random, others are caused by environmental factors cause changes in genes. When new forms of a gene appear because of mutation, a rapid change in a species may happen if the environment changes. Such rapid changes support the theory of evolution by natural selection.

Peppered moths

Before the industrial revolution in Britain, most peppered moths were of the pale variety, meaning that they were camouflaged against the pale birch trees that they rest on. Moths with a mutant black colouring were easily spotted and eaten by birds. This gave the white variety an advantage and they were more likely to survive to reproduce.

Airborne pollution in industrial areas then blackened the birch tree bark with soot. This meant that the mutant black moths were now camouflaged, while the white variety became more vulnerable to predators. The black variety now had the advantage and were more likely to survive and reproduce. Over time, black peppered moths have become far more numerous in urban areas.

The pale peppered moths camouflage well against the pale birch tree

The darker mutant peppered moths camouflage well against the blackened birch tree

Antibiotic-resistant bacteria

Microorganisms such as bacteria and viruses reproduce very rapidly. They can evolve in a relatively short time. One example is the bacterium E. coli. Its DNA [DNA: The material inside the nucleus of cells, carrying genetic information. DNA stands for Deoxyribonucleic Acid. ] can be damaged or changed when it reproduces. Most of the time this causes the death of the bacterial cell.

Occasionally, the mutation is beneficial for the bacterial cell. For example, it may allow resistance to an antibiotic. When that antibiotic is present, the resistant bacteria have an advantage over bacteria that are not resistant.

Antibiotic-resistant strains of bacteria are an increasing problem in hospitals.

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