The years in which two species share a common ancestor if the molecules found in these two species differ by a total of six mutations is 72 million years.
Mutation is the changing of gene or characters of any species over time, there are many reasons for mutation, like natural selection.
Every 12 million years, the molecular clock will mutate.
If the molecular clock experiences six mutations, 12 million years multiplied by 6 have passed.
12 x 6 = 72
Thus, the years are 72 million years. Option is b.
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