The independent role of morphology in mate choice is revealed by the rare instances where the usual association between song and morphology is disrupted.
Peter R. Grant
Evidence of epistasis from hybridization studies is more scarce.
To summarize, the particular song a male sings, and the behavioral responses of females to song and morphological signals, are not genetically inherited in a fixed manner but are determined by learning early in life.
The theory of founder effects does not explain how novel features like plumage traits arise.
We observe closely related species in sympatry and infer how they evolved from a common ancestor.
Thus the genetic basis to the origin of bird species is to be sought in the inheritance of adult traits that are subject to natural and sexual selection.
Species can be recognized by their morphological characteristics and songs.
Thus mating of females was strictly along the lines of paternal song.
Genes that underlie the capacity to receive, use and transmit information are the evolving properties.
Exchange of breeding individuals between two populations tends to homogenize their gene pools.
The divergence of songs in the new population away from those in the progenitor population would only be prevented if these processes were balanced by repeated immigration and subsequent breeding: song flow.
Islands are known to differ in the food supply available to ground finches, mainly seeds.
Plumage features constitute a major component of courtship signals.
Males transmit signals in courtship through behavioral displays.
Almost nothing is known from hybridization studies about the inheritance of courtship behavior of females, or of their responsiveness to particular male signals.
Closely related species of birds are also chromosomally similar.
The process of speciation is completed with the cessation of genetic exchange.
