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Alternatively, instead of a maximum and a minimum, a prior probability of the divergence time can be established and used to calibrate the clock.

Simulation studies have shown that increasing the number of fossil constraints increases the accuracy of divergence time estimation.If this is correct, the cytochrome c of all mammals should be equally different from the cytochrome c of all birds.Since fish diverges from the main stem of vertebrate evolution earlier than either birds or mammals, the cytochrome c of both mammals and birds should be equally different from the cytochrome c of fish.If most changes seen during molecular evolution are neutral, then fixations in a population will accumulate at a clock-rate that is equal to the rate of neutral mutations in an individual.The molecular clock alone can only say that one time period is twice as long as another: it cannot assign concrete dates.