The Birth Order Effect on Sexual Orientation

This chapter explores the biological factors influencing male homosexuality, particularly the birth order effect which correlates the number of older brothers with the likelihood of identifying as gay. It discusses the role of the uterine environment, maternal immune response, and the impact of older siblings, alongside insights from twin studies and hormonal influences. The chapter emphasizes the need for further research to understand the complex interplay between genetics, hormonal exposure, and sexual orientation.