PUNCTUATED EVOLUTION CAUSED BY SELECTION OF RARE BENEFICIAL MUTATIONS

For more than two decades there has been intense debate over the hypot hesis that most morphological evolution occurs during relatively brief episodes of rapid change that punctuate much longer periods of stasis , A clear and unambiguous case of punctuated evolution is presented fo r cell size in a population of Escherichia coli evolving for 3000 gene rations in a constant environment, The punctuation is caused by natura l selection as rare, beneficial mutations sweep successively through t he population, This experiment shows that the most elementary processe s in population genetics can give rise to punctuated evolutionary dyna mics.