9.1 Chapter Objectives

Learning Objectives

Our objective for this chapter is to present some patterns related to observed male:female sex ratios, in both human and non-human populations. We’ll also discuss several factors affecting sex ratios, and hypotheses for understanding skewed sex-allocation phenomena. By the end of your reading and our in-class discussion, you will be able to:

    1. Define the following terms:
      • operational sex ratio
      • sex allocation
    2. List the three key factors that influence population sex ratios
    3. Describe the Trivers-Willard hypothesis for sex allocation, and cite evidence in support of this hypothesis
    4. Explain alternative hypotheses for explaining skewed sex ratios in organisms with chromosomal (genetic) sex determination