In natural selection, how does the mutation rate affect the speed at which a population adapts to its environment? In artificial selection, scientists doing artificial breeding experiments often use radiation or other methods to increase the mutation rate. Why is a high mutation rate useful? 

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The mutation rate is the speed (or mutations per unit time) at which a sequence of DNA changes, either through natural means or artificially induced means.  Natural selection is the way that a population of organisms evolve over time to adapt to their environment.  Populations change as a result of organisms with beneficial traits surviving and mating to pass on these traits to future generations while organisms without these traits die off.  These traits are often distributed by means of mutation.  Random mutations will give rise to a distribution of traits.  The faster the mutation rate, the faster the beneficial traits will manifest themselves and work themselves into the genetic fabric of the organism population.  But if the mutation rate is too high, the genetic drift will be too large for the desired mutations to take hold.  For artificial selection, scientists are trying to alter the genes of an organism on a useful timeframe.  Natural selection takes place over numerous generations and thousands of years.  Scientists use a directed mutation to increase the rate to breed on a useful timeframe.

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