Alpine Swift (Apus melba) Science Article 9
Two mutually exclusive hypotheses have been put forward to explain the evolution and adaptive function of melanin-based color traits. According to sexual selection theory melanism is a directionally selected signal of individual quality, whereas theory on the maintenance of genetic polymorphism proposes that alternative melaninbased variants achieve equal fitness.
PIERRE BIZE et al, Evolution, 60(11), 2006, pp. 2370-2380