The Directed Mutation Controversy and Neo-Darwinism

According to neo-Darwinian theory, random mutation produces genetic
differences among organisms whereas natural selection tends to increase the
frequency of advantageous alleles. However, several recent papers claim
that certain mutations in bacteria and yeast occur at much higher rates
specifically when the mutant phenotypes are advantageous. Various molecular
models have been proposed that might explain these directed mutations, but
the models have not been confirmed. Critics contend that studies purporting
to demonstrate directed mutation lack certain controls and fail to account
adequately for population dynamics. Further experiments that address these
criticisms do not support the existence of directed mutations.