1. Chapter 1 Opener: Charles Darwin’s study

2. 1.1 The monogamous prairie vole

3. 1.2 The brain of the prairie vole is a complex, highly organized machine

4. 1.3 A gene that affects male pairing behavior in the prairie vole

5. Box 1.1 How are phylogenetic trees constructed and what do they mean?

6. 1.4 The evolutionary relationships of the prairie vole and six of its relatives

7. 1.5 The possible history behind monogamy in the prairie vole

8. 1.6 The connection between evolutionary history and the mechanisms of behavior

9. 1.7 Testing the hypothesis that monogamy in prairie voles is linked to a specific gene

10. 1.8 Charles Darwin, shortly after returning from his around-the-world voyage on the Beagle

11. 1.9 A variable species

12. 1.10 Natural selection

13. 1.11 A band of Hanuman langur females and their offspring

14. 1.12 Male langurs commit infanticide

15. 1.13 Variation in suicidal tendencies in a make-believe lemming-like species

16. 1.14 Infanticide by a male lion

17. 1.15 An evolved response to the risk of infanticide