The evolution of dominance by the selection of modifiers
of the phenotypes of deleterious
mutations was proposed as a hypothesis by R. A. Fisher in 1928. It
has been strongly criticized
ever since, is regarded by many as having been made irrelevant by
metabolic control theory,
and most recently has been claimed to have been ‘falsified’
by H. A. Orr. Is it indeed not only
obsolete but wrong? Its history is reviewed and its present status
evaluated. We conclude (1)
that it has a role as the explanation of the dominance found in many
cases of selection through
visual predation and (2) that the selection mechanism long claimed to
be ineffective (the
increase in frequency of a single modifier) will be effective under
certain special conditions that
may be different from those Fisher proposed.