A molecular clock can only work if the molecule used to make the tree is changing at a similar rate in each lineage in a phylogeny.

Question

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A molecular clock assumes that the molecular changes are accumulating at a relatively constant rate across different lineages. However, this assumption may not hold if the rate of molecular change varies significantly in different lineages or if there are factors that influence the rate of molecular evolution, such as natural selection, genetic drift, or environmental factors. Therefore, the validity and accuracy of molecular clocks depend on the extent to which the assumption of a constant molecular rate holds in a given phylogeny.

A Molecular Clock Can Only Work If the Molecule Used