Table of Contents

Introduction

Chapter 1: What Is Sexual Orientation?
Criteria for sexual orientation
Sexual orientation in men and women
Stability of sexual orientation
Prevalence of different orientations
Are there categories?
Sexual orientation across cultures

Chapter 2: Why We Need Biology
Psychoanalytic theories
Learning theories-influence of early sexual experiences
Childhood abuse
Learning theories-gender learning
Is it a choice?
The biological alternative

Chapter 3: The Outline of a Theory
Male and female brains
Male and female behaviors
Development of sex differences in animals
Sexual partner preference in animals
Origins of variation within each sex
Relevance to human sexual orientation
Sexual orientation in nature

Chapter 4: Childhood
Development of gendered childhood traits
Childhood traits associated with adult sexual orientation: retrospective studies
Prospective studies
Contrasting models

Chapter 5: Characteristics of gay and straight adults
Gendered traits in adulthood
Origin of gendered traits
Sexual orientation and cognitive traits: visuospatial abilities
Verbal fluency
Memory tasks
Handedness
Olfaction
Intelligence
Personality traits: Masculinity-femininity
Occupational preferences
Other personality traits
Sexuality
Overview

Chapter 6: The role of sex hormones
Hormone levels in gay and straight adults
Why focus on prenatal sex hormones?
Hormone levels during development
Congenital adrenal hyperplasia
Finger length studies
The inner ear
Central auditory system
Action of sex hormones on the developing brain
Possible causes of variability in prenatal androgen levels

Chapter 7: The role of genes
Sibling studies
Is the family clustering caused by genes?
Twin studies
Molecular genetics-candidate-gene studies
Genome scans
Genes and sexuality in fruit flies
Genes, homosexuality, and evolution
Kin selection
The "fertile female" hypothesis
Beneficial effects on same-sex relatives

Chapter 8: The brain
A brief tour of the brain
The hypothalamus and sexual orientation
Other brain regions
Brain activity
Chemosignals
Stress response
Functional lateralization
Sheep
Inhibition and sexual orientation
Overview

Chapter 9: The body
Body size and shape
Trunk and limb length
Penis size
Sturcture of the face
Hair whorl direction
Gaydar
Overview

Chapter 10: The older-brother effect
How well established is the older-brother effect?
How strong is the older-brother effect?
The older-brother effect and handedness
What causes the older-brother effect?

Chapter 11: Beyond gay and straight
Bisexuality in men
Bisexuality in women
Asexuality
Age preference and pedophilia
Butch-femme and top-bottom
Transgender/transexuality


Chapter 12: Conclusions
Sexual orientation is linked to other gendered traits
A common origin for gender-shifted traits?
The role of genes
Does the older-brother effect work through prenatal hormones?
Is there a random biological influence?
How does sexual orientation become categorical?
Unconscious processes in sexual attraction and arousal
Changes in the prevalence and nature of homosexuality
What is sexual orientation?
Sexual orientation and gender: the social fallout
Glossary
Bibliography

About the Author

Simon LeVay, PhD, has served on the faculties of Harvard Medical School and the Salk Institute for Biological Studies. He has written eleven books, including the New York Times best-seller When Science Goes Wrong (2008) and the textbook Discovering Human Sexuality (2015).

Reviews

"Although the book's chief appeal probably will be to professionals dealing with these issues, other interested readers will find it an informative and generally approachable read." --Publishers Weekly
"Simon LeVay, a former Harvard neuroscientist, has written, Gay, Straight, and the Reason Why: The Science of Sexual Orientation, a comprehensive, engaging and occasionally quite funny look at the current state of the research on the topic." --Schuyler Velasco, Salon
"This book will serve both as a resource for researchers looking for what is yet unknown and what questions need further research and as a fascinating read for the educated layperson, who will be intrigued by some of the factors that may relate to homosexuality... Recommended." --Choice
"LeVay also does a nice job illustrating that the argument for sexual orientation as determined is not a singular cause-and-effect argument...Yet, it is important for scholars and clinicians alike across various paradigms to be aware of the research reviewed in Gay, Straight, and the Reason Why." --PsycCritiques
"Simon LeVay's book, Gay, Straight, and the Reason Why, offers an excellent review of scientific research on the causes and correlates of sexual orientation. It provides a clear and comprehensive summary of recent studies of sexual orientation- a review that should be useful to lay people and journalists as well as to professionals in the field. LeVay has a knack for describing complicated scientific topics- brain anatomy, behavior genetics, endocrinology,
cognitive psychology- in straight-forward and easy-to-understand ways. He provides the reader with a good sense of where research on sexual orientation stands today, and where further research is needed."
-- Richard Lippa, Sex Roles
"The theory that sexual orientation has a biological basis receives support in neuroscientist Simon LeVay's book. Relating evidence from genetics, neuroscience and developmental biology, he suggests that prenatal interactions between hormones and the developing brain influence adult sexuality." -- Nature