Molecular clock

**1. Development and Theory of Molecular Clocks:**
– Molecular clock concept attributed to Zuckerkandl and Pauling in 1962
– Genetic equidistance noted by Margoliash in 1963
– Sarich and Wilson’s 1967 study showed constant rates of change in Primates
– Relationship with Kimura’s neutral theory predicting a molecular clock
– Neutral mutations accumulate at a clock-rate in a population
– Most changes in molecular evolution are predicted to be neutral
– Fixations in a population accumulate at the rate of neutral mutations

**2. Calibration of Molecular Clocks:**
– Molecular clocks need calibration for estimating divergence times
– Calibration methods include node and tip calibration
– Fossil record is often used to calibrate molecular clocks
– Node calibration specifies time constraints for nodes in phylogenetic trees
– Tip calibration uses fossils treated as taxa and placed on tree tips

**3. Techniques and Methods in Molecular Clock Research:**
– Bayesian methods offer better divergence time estimates with large datasets
– Relaxed molecular clocks consider rate variation across lineages
– Statistical approaches like maximum likelihood techniques improve estimates
– Divergence dates from molecular clocks are based on statistical inference
– Fossilized birth-death process for calibration
– Bayesian total-evidence dating

**4. Challenges and Critiques of Molecular Clocks:**
– Divergence rates vary across species and genomic regions
– Factors like generation times and population size affect molecular clock analysis
– Variation in rate among taxa challenges molecular clock hypothesis
– Molecular clock faces challenges at very short and very long timescales
– Major analytical and conceptual shortcomings in taxonomic revisions
– Evolutionary changes occur suddenly

**5. Applications and Further Reading on Molecular Clocks:**
– Molecular clock aids in molecular systematics, macroevolution, and phylogenetics
– Estimates dates of phylogenetic events, including those without fossil evidence
– Calibrated phylogenies are crucial for phylogenetic comparative methods
– Notable publications on molecular clock theory and practice
– The Molecular Evolutionary Clock: Theory and Practice
– Molecular clocks: four decades of evolution