The Fitness Valley
Warning coloration (aposematism) only works after predators have learned to avoid it. But the first conspicuous individual appears before any predator has learned — and should be eaten at a higher rate than the camouflaged population it came from. Between camouflage (a local fitness peak) and full aposematism (a higher global peak) lies the valley: conspicuous, but not yet avoided.
The fitness valley is a formal problem in population genetics. A population at a local optimum cannot reach a higher global optimum by gradual steps if the intermediate states all have lower fitness. Three proposed routes across the aposematism valley are shown here:
Kin selection: Aposematic individuals are often siblings. Each sacrifice generates amplified predator learning — relatives sharing the warning-color gene benefit collectively from the lesson.
Neophobia: When the warning signal is novel (rare), predators sometimes hesitate before attacking unfamiliar phenotypes. This gives the first aposematic individuals time to multiply before full predation pressure arrives.
Maternal effect gene (Brodie et al., PNAS 2001): Heterozygous (c/a) carriers express aposematic phenotype in their offspring, not themselves. The first c/a mutation is invisible to selection and enters the population as a full cohort of phenotypically aposematic individuals — already on the far side of the valley before selection can act on the allele.