Question

Why might the molecular clock run faster for some lineages and not others? What hypothesis would be consistent with an observed pattern of faster molecular evolution? Or slower molecular evolution?

Answer 1

The Neutral Theory forms the basis of the molecular clock hypothesis. The mutational changes in DNA are inherited over the generations. The number of heritable DNA mutations that result in the protein substitutions which accumulate overtime decide the rate of evolution. Therefore the molecular clocks of some lineages are faster than the others. For example, the vertebrates have faster evolution rate as compared to the primates. But the monkey lineage evolved faster than the human lineage. The rate-constancy hypothesis would be consistent with an observed pattern of faster molecular evolution. The molecular clock is of 2 types: metronomic clock and stochastic clock. The slower molecular evolutions can be described by the local molecular clocks.