The fossil record shows that many species remain constant for long periods of time, but then speciation episodes occur rapidly. this is best described as

The biological theory describing the rapid events of speciation among many species that remained constant for long periods of time is known as punctuated equilibrium. This theory suggests that many species undergo least amount of change over the time remaining constant and stable until some rare events such as cladogenesis, which causes significant evolutionary changes to occur.

Hence, the correct answer is 'punctuated equilibrium'.

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i guess you forgot putting it.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.