The high prevalence in malaria-endemic areas of G6PD mutants that have arisen independently corroborates this notion; indeed, it constitutes an example of convergent evolution through balanced polymorphism.
2.
Balanced polymorphism could arise when a predator like the song thrush has a given'search image', so it tends to see and kill snails of a particular colour and pattern.
3.
If predators switch between host plants that provide toxins and plants that do not, depending on the abundance of larvae on each type, then automimicry may be maintained in a balanced polymorphism.
4.
Researchers have variously asserted that the cause is random genetic drift, different natural selection pressures in different areas ( the snail often has darker camouflage in woodland, lighter in rough grassland ) with mixing by migration, and balanced polymorphism.
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