Fig 3. Schematic pictures that show the relations among chronological and retrospective phenotype distributions, fitness landscape, and selection strength.

A. Weak selection. When the chronological (green) and retrospective (pink) probability distributions are similar, the fitness landscape h(x) largely does not change over the range of phenotypic values x, and the selection strength S[x] is approximately 0. B. Strong selection. When the retrospective probability distribution significantly deviates from the chronological distribution, the fitness landscape h(x) changes greatly over the range of phenotypic values x. In this case, the selection strength S[x] is greater than zero.