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.
From Peter R. Grant
Almost nothing is known from hybridization studies about the inheritance of courtship behavior of females, or of their responsiveness to particular male signals.
We observe closely related species in sympatry and infer how they evolved from a common ancestor.
Males transmit signals in courtship through behavioral displays.
Plumage features constitute a major component of courtship signals.
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.
Evidence of epistasis from hybridization studies is more scarce.
Closely related species of birds are also chromosomally similar.
The theory of founder effects does not explain how novel features like plumage traits arise.
The process of speciation is completed with the cessation of genetic exchange.
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