near neutrality
Ohta T 1972 Population size and rate of evolution. J Mol Evol 1:305-314.
- there is much substitution of nearly neutral mutations, for which the selection intensity varies from time to time or from region to region
- the hypothesis presented here is that evolution is more rapid in small populations than in large ones
- in a stable environment a random mutant need be beneficial only under restricted circumstances to have a selective advantage
- Fisher argued that the most favorable population for evolutionary change is a large one, both because of its greater genetic variability and because random processes are less important
- Wright, in his shifting balance theory, places great importance on random gene frequency drift
- but he regards the most favorable structure as being a population subdivided into groups
- my theory emphasizes random changes, but considers the evolution within the restricted population rather than the effect of migrants
- it also differs from a strict neutral theory in that in the latter, the rate of evolution is independent of the population size
- not only disadvantageous gene substitutions but also advantageous ones can increase when the population size gets small in our model
