A molecular clock assumes that the genes used are evolving rapidly. do not alter their rates in different lineages. are evolving slowly. are all evolving at the same rate. alter their rates in different lineages.
A molecular clock is actually an estimation method. It is used to approximate the time taken for major evolutionary events to take place based on the changes in the orthologous genes (genes that are passed by vertical descent).
In making the estimation, the molecular clock assumes that the genes used are all evolving at the same rate.
