The genetic and the operative evidence relating to secondary sexual characters

by Thomas Hunt Morgan

"The Genetic and the Operative Evidence Relating to Secondary Sexual Characters" by T.H. Morgan is a scientific publication written in the early 20th century. This work delves into the genetic and physiological aspects of secondary sexual characteristics in birds, particularly focusing on the Sebright bantam and other fowl as subjects for analysis. It covers various experiments and findings related to plumage differences between hen-feathered and cock-feathered males, exploring how these traits are influenced by factors such as heredity and endocrine signaling. The opening of the book sets the stage for an in-depth study of the genetic mechanisms at play in determining secondary sexual characteristics. It begins with a discussion of the existence of two male types within certain poultry breeds and introduces the author's experimentation with castrating hen-feathered Sebrights to observe changes in plumage. Morgan recounts his observations regarding the physical alterations in feathering post-operation, revealing insights into the relationship between the gonads and plumage expression. This portion establishes not only the methodology and initial findings but also hints at the broader implications for understanding sexual differentiation in birds.