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Statistical models of the overdispersed molecular clock.
1National Institute of Genetics, Mishima, Japan.
Theoretical Population Biology
|June 1, 1991
Summary
Molecular clock models often assume a Poisson process, but recent data show overdispersion. This study explores temporal variation as a cause, suggesting major molecular changes or selection drive evolutionary rate shifts.
Area of Science:
- Evolutionary Biology
- Molecular Evolution
- Statistical Modeling
Background:
- The molecular clock hypothesis posits constant evolutionary rates, often modeled by a Poisson process where variance equals mean.
- Recent sequence data reveal significant overdispersion (variance > mean) in molecular evolution, challenging the simple Poisson model's generality.
Purpose of the Study:
- To investigate the causes of overdispersion in molecular evolution.
- To review and compare statistical models accounting for temporal variation in evolutionary rates.
- To examine the role of selected substitutions in molecular evolution.
Main Methods:
- Statistical analysis of molecular evolution data.
- Review of existing and proposed statistical models for molecular clock variation.
- Quasi-quantitative examination of selected substitutions.
Main Results:
- Spatial (site-specific) variation is unlikely to be the primary cause of overdispersion.
- Temporal variation in evolutionary rates is a more probable explanation.
- Overdispersion may result from major molecular reconfigurations or post-change selection.
Conclusions:
- Temporal variation models offer better explanations for observed overdispersion in molecular evolution.
- Distinguishing between models can provide insights into evolutionary mechanisms.
- Selected substitutions after major changes might occur without invalidating the broader neutral theory.