 Subsequently, Tomoko Ohta began to argue for a more significant role for weakly selected mutants (Ohta 1973). Essentially, Ohta’s definition of “nearly neutral” includes mutants that are less neutral than Kimura’s “nearly neutral” mutants, and larger amounts of them as well (Dietrich and Millstein 2008). Later refinements included both slightly deleterious and slightly advantageous mutants. This changes the processes that one would expect to be acting. With the (strictly) neutral theory, only drift would act on the neutral mutants. With the nearly neutral theory, the nearly neutral mutations (whether advantageous or deleterious) would subject to very weak selection (discriminate sampling) and to drift in the form of indiscriminate gamete sampling (Dietrich and Millstein 2008). Because the selection is weak, it would be swamped by the effects of drift, but both processes would still be occurring. Ohta believed that the nearly neutral theory could better account for the results found by Ayala and his colleagues (with its large number of relatively rare alleles), and also, that it could better explain some features of the molecular clock (Dietrich and Millstein 2008). However, it has proven much more difficult to find unique outcomes for the nearly neutral theory than the neutral theory. This makes the nearly neutral theory more difficult to test for and less useful as a null hypothesis as compared to the neutral theory, even as it might account for the available data better.