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Natural selection and evolution

Evidence for natural selection

Rapid changes in species have been observed. These support the theory of evolution.

Peppered moths

Before the industrial revolution in Britain, most peppered moths were of the pale variety. This meant 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 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. This gave the black variety an advantage, and they were more likely to survive and reproduce. Over time, the black peppered moths became far more numerous in urban areas than the pale variety.

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

E. coli bacteria (Photo from Rocky Mountain Laboratories, NIAID, NIH)

Microorganisms such as bacteria and viruses reproduce very rapidly and 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 during replication, and most of the time this causes the death of the cell. But occasionally, the mutation is beneficial - for the bacteria. For example, it may allow resistance to an antibiotic. When that antibiotic is present, the resistant bacteria have an advantage over the bacteria that are not resistant. Antibiotic-resistant strains of bacteria are an increasing problem in hospitals.

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