Figure 1 .

The relationship between the fraction of mutations that are beneficial, ε, and the absolute fitness of the population, ω. A poorly adapted population (green) with $\stackrel{-}{\omega }<{\omega }_{\text{c}}$ and ε < ε_c will adapt toward the dynamic equilibrium “attractor” state (gray) with higher fitness and lower ε. Conversely, an “overadapted” population (red) with $\stackrel{-}{\omega }>{\omega }_{\text{c}}$ and ε < ε_c will decline in fitness toward the dynamic equilibrium state due to Muller’s ratchet.