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Punctuated evolution caused by selection of rare beneficial mutations
S F Elena1, V S Cooper, R E Lenski
1Center for Microbial Ecology, Michigan State University, East Lansing, 48824, USA. selena@ant.css.msu.edu
Science (New York, N.Y.)
|June 21, 1996
Summary
Punctuated evolution, where rapid changes interrupt long stable periods, was observed in Escherichia coli cell size over 3000 generations. Natural selection driving beneficial mutations caused these evolutionary punctuations, demonstrating basic population genetics principles.
Area of Science:
- Evolutionary Biology
- Microbial Evolution
- Population Genetics
Background:
- The theory of punctuated equilibrium proposes that evolution is characterized by long periods of stasis interrupted by short bursts of rapid change.
- Debate continues regarding the prevalence of this pattern in morphological evolution.
Purpose of the Study:
- To provide a clear experimental case for punctuated evolution.
- To investigate the dynamics of cell size evolution in Escherichia coli under controlled conditions.
Main Methods:
- Culturing a population of Escherichia coli for 3000 generations in a constant environment.
- Monitoring cell size as a measure of morphological evolution.
- Analyzing the role of natural selection and mutation dynamics.
Main Results:
- Observed distinct episodes of rapid cell size increase punctuating longer periods of stasis.
- Identified natural selection acting on rare, beneficial mutations as the driving force behind these rapid changes.
- Demonstrated that fundamental population genetics processes can generate punctuated evolution.
Conclusions:
- The study provides unambiguous experimental evidence for punctuated evolution in cell size.
- Natural selection acting on successive beneficial mutations is a key mechanism driving punctuated evolutionary dynamics.
- This finding supports the hypothesis that punctuated change is a significant mode of evolution.