polygenic adaptation

Kimura M 1981 Possibility of extensive neutral evolution under stabilizing selection with special reference to non-random usage of synonymous codons. PNAS 78:5773-5777.

• if the deviation of the mean from the optimum is much larger than the effect of the allele substitution (|m≫|a|), we have s / a ≈ − λm
• the situation is similar to truncation selection
• natural selection acts very efficiently to change the mean toward the optimum
• during this short period of directional selection, extensive shift of gene frequencies is expected to occur at many loci
• this process itself will seldom cause gene substitutions

• the present analysis agrees with Lande (35), who suggests that many polygenic changes can accumulate by random drift because they have little or no net phenotypic effect