neutrality versus near neutrality

Takahata N 1996 Neutral theory of molecular evolution. Curr Opin Genet Dev 6:767-772.

Kimura was once sympathetic to the 'slightly deleterious' hypothesis of Ohta when criticisms against the neutral theory were most intense
he himself proposed the 'effectively neutral' model in 1986
nevertheless, in his last few years, Kimura abandoned this ad hoc model and returned to the original neutral theory
it was at this time that Ohta renamed her previously proposed hypothesis as 'nearly neutral'
although 'slightly deleterious' and 'nearly neutral' sound similar, there is an important difference
under a model of near-neutrality, one half of the mutations are implicitly assumed to be advantageous
needless to say, the concept of near-neutrality is no longer the same as that of Kimura's neutrality

it is claimed that the nearly neutral theory can explain the widest range of phenomena
although it is highly model-dependent
this paper remarks that near-neutral no longer implies deleterious

a model of near-neutrality is shown here to be incompatible with most of the major features of protein evolution
but not with a model of evolution by exclusively deleterious mutations
an ironic paper from the proponent of the slightly deleterious theory who subsequently abandoned it [16*], recently developing the near-neutral theory