How Do Traits Change Across a Scrub-Jay Hybrid Zone?
Where should we draw the line between species? Biologists have debated this question for over 100 years. For much of that time, Ernst Mayr’s Biological Species Concept, which defines a species as a group of individuals that is reproductively isolated from other groups, has dominated the conversation. Recently, however, more and more evidence of hybridization between species has accumulated, especially in birds.