21 Metric characters under natural selction

21.1 Natural selection

21.1.1 Fitness and its components

21.2 Relationships between metric characters and fitness

21.2.1 Fitness profiles

21.3 Responses to natural selection

21.3.1 Fitness

21.3.2 Correlated responses

21.3.3 Strength of selection

21.4 Equilibrium populations

21.4.1 Fitness

21.4.2 Major components

21.4.3 Characters with intermediate optima

21.4.4 Characters with minimum fitness of intermediates

21.4.5 Neutral characters

21.5 Origin of variation by mutation

21.5.1 Mutational variance

21.6 Maintenance of genetic variation

21.6.1 Balance between neutral mutation and random drift

21.6.2 Mutation-selection balance