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What is the molecular clock?
A molecular clock is not like a mechanical
time piece. It is a stochastic clock. Individual "clicks''
of the clock will not occur with perfect time periods separating
them, but enough "clicks'' of the clock should have an expectation
that is constant. The clock is sloppy. The question is: how
sloppy can it be and still be considered a clock? This is
the Problem of Variability.
There are two reasons for being interested
in the molecular clock:
(1) The clock can help establish a time scale
for evolution.
(2) The clock has important implications for
our understanding of the mechanisms of molecular evolution.
The relationships between the molecular clock and timescales
and mechanisms have both been controversial.
The reliability of the molecular clock as a means of estimating
evolutionary timescales has been called into question in a
numerous specific cases. See Slowdowns
and Speedups for more.
Very soon after the molecular clock was introduced, a neutralist
mechanism was proposed. For more on the clock and its putative
mechanisms see the
Neutralist Mechanism.
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