- Title Pages
- Chapter 1 Why Are There Two Sexes?
- Chapter 2 Sex Differences in the Brain: What’s Old and What’s New?
- Chapter 3 Research and Methodological Issues in the Study of Sex Differences and Hormone-Behavior Relations
- Chapter 4 Methodological Issues in the Study of Hormone-Behavior Relations in Humans: Understanding and Monitoring the Menstrual Cycle
- Chapter 5 Sex Differences in Pharmacogenomics as a Tool to Study CNS Disorders
- Chapter 6 Sex Differences in HPA Axis Regulation
- Chapter 7 Steroid Hormone Receptors and Sex Differences in Behavior
- Chapter 8 Sex Differences in Affiliative Behavior and Social Bonding
- Chapter 9 Sex Differences in the Organization of Movement
- Chapter 10 Sex Differences in Motivation
- Chapter 11 Sex Differences in Neuroplasticity
- Chapter 12 Sex Differences in Cognitive Function in Rodents
- Chapter 13 Sex Differences in Energy Metabolism, Obesity, and Eating Behavior
- Chapter 14 Sex Differences in Children’s Play
- Chapter 15 Sex Differences in the Neurocognition of Language
- Chapter 16 Endocrine Contributions to Sex Differences in Visuospatial Perception and Cognition
- Chapter 17 Sex Differences in Infectious and Autoimmune Diseases
- Chapter 18 Sex Differences in Neuroimmunology
- Chapter 19 Sex Differences in Pain
- Chapter 20 Sex Differences in Anxiety Disorders
- Chapter 21 Hormones and Mood
- Chapter 22 Sex Differences in Brain Aging and Alzheimer’s Disorders
- Chapter 23 Sex Differences in Parkinson’s Disease
Why Are There Two Sexes?
Why Are There Two Sexes?
- (p.2) (p.3) Chapter 1 Why Are There Two Sexes?
- Sex Differences in the Brain
- Oxford University Press
This chapter provides a three-part introduction to sex differences, stressing both the conserved and the unique as part of Darwin's notion of descent with modification. The first section takes a step back in time and provides a broad perspective on the evolution of eukaryotes. The evolution of meiosis and syngamy (i.e., the fusion of two cells) was a precondition for the evolution of dimorphic gametes and the subsequent evolution of all other sex differences. It then outlines general causes of sex differences in animals by focusing on natural and sexual selection. The second section discusses the mechanisms that underlie sex differences in gene expression as well as the basic developmental mechanisms that produce sex differences. The third section reviews some elegant research that links evolutionary causes of and proximate mechanisms for sex differences in the brain and behavior. These examples show how sex-specific selection on behavior ultimately drives neural evolution. The chapter concludes by briefly outlining what is known about sexual differentiation of neural mechanisms in humans.
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