Further Thought

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Further Thought

Use the questions at the end of the chapter to explore concepts and connections in greater depth through application and synthesis.

1. Suppose adult bee-eaters could raise only 0.3 more offspring with a helper than without a helper. Would you still expect male bee-eaters to give in to the harassment of their fathers, or would male bee-eaters tend to fight off their fathers? Explain your reasoning. [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

2. When a Thomson's gazelle detects a nearby stalking cheetah, the gazelle often begins bouncing up and down with a stiff-legged gait called stotting (see Figure 11.24 on page 450 in your textbook). One hypothesis is that stotting has evolved because it may help alert the gazelle's kin to the presence of a predator, analogous to the alarm calls of ground squirrels. Caro reports that stotting does not seem to increase the gazelle's risk of being attacked. In fact, once a gazelle begins to stott, the cheetah often gives up the hunt. How is C (the cost of stotting) different for a gazelle, compared to C (the cost of alarm calls) for a ground squirrel? Do you think it is likely that stotting is an altruistic behavior? With this in mind, make a prediction about whether a gazelle will stott when there are no other gazelles around, and then look up Caro's papers to see if you are right.

Caro, T. M. 1986. The function of stotting in Thomson's gazelles: Some tests of the hypotheses. Animal Behaviour 34: 663–684.

Caro, T. M. 1994. Ungulate antipredator behaviour: Preliminary and comparative data from African bovids. Behaviour 128: 189–228. [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

3. The cubs of spotted hyenas often begin fighting within moments of birth, and often one hyena cub dies. The mother hyena does not interfere. How could such a behavior have evolved? For instance, from the winning sibling's point of view, what must B (benefit of siblicide) be, relative to C (cost of siblicide), to favor the evolution of siblicide? From the parent's point of view, what must B be, relative to C, for the parent to watch calmly rather than to interfere? For more about the unusual social system of spotted hyenas and for new information from studies of wild hyenas, see:

Frank, Laurence G. 1997. Evolution of genital masculinization: Why do female hyaenas have such a large 'penis'? Trends in Ecology and Evolution 12: 58–62.

Golla, W., H. Hofer, and M. L. East. 1999. Within-litter sibling aggression in spotted hyaenas: Effect of maternal nursing, sex and age. Animal Behaviour 58: 715–726. [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

4. Blue jays (Cyanocitta cristata) seem to be better than American robins (Turdus migratorius) at recognizing individuals. In one study, blue jays raised with American robins could distinguish strange from familiar robins better than the robins themselves. Do you think these species differ in occurrence of kin selection or reciprocal altruism (or both)? Why? See:

Schimmel, K. L, and F. E. Wasserman. 1994. Individual and species preference in two passerine birds: Auditory and visual cues. Auk 111: 634–642. [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

5. The first paragraph of this chapter refers to crows who cooperate in chasing a predator away (a behavior known as mobbing) and who help their parents raise their siblings. Which behavior is mutualistic, and which behavior is favored by kin selection? Suggest a hypothesis to explain why young crows in some populations might help at the nest, while in other populations they nest on their own. [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

6. The biologist J. B. S. Haldane was once explaining kin selection to some friends in a pub. As the story goes, he scribbled some calculations on an envelope and announced that he would be willing to die for two brothers or eight cousins. Explain his reasoning. [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

7. Look at Figure 11.18 (page 440 in your textbook) on parent–offspring conflict. Explain, in general terms, why the behavior of females should evolve so that mothers start weaning when B/C falls below 1. (Hint: Consider the reproductive success of mothers who wean very early and of mothers who wean very late.) If a mother could have only one litter of young in her lifetime, how would the period of weaning conflict change? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

8. The text claims that eusociality has evolved several times independently within the hymenoptera. What is the evidence for this statement? If it is true, in what sense is eusociality in ants, bees, and wasps an example of convergent evolution (see Chapter 14)? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

9. How would you go about testing the hypothesis that female lions who do not participate in territory defense reciprocate by providing milk to the offspring of territory defenders? List the predictions made by the hypothesis and the types of data you would have to collect. [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

10. House sparrows often produce two successive broods of young. Males feed their first brood only briefly, but feed their second brood for much longer. Why do males feed first broods less than second broods? (Hint: Consider how C, the cost of feeding the current brood, changes.) How could you test your hypothesis? How is this situation analogous to weaning conflict in mammals? See:

Hegner, R. E., and J. C. Wingfield. 1986. Behavioral and endocrine correlates of multiple brooding in the semicolonial house sparrow Passer domesticus. I. Males. Hormones and Behavior 20: 294–312. [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

11. Which is more common in human cultures—eusociality (look back at the three requirements of eusociality; can you think of any human cultures that fit?), or a helper-at-the-nest social system? Which do you think is generally more common in social animals? Why? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

12. Human siblings often show intense sibling rivalry that typically declines during the teenage years. Suggest an evolutionary explanation for this pattern. [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.




1.	Suppose adult bee-eaters could raise only 0.3 more offspring with a helper than without a helper. Would you still expect male bee-eaters to give in to the harassment of their fathers, or would male bee-eaters tend to fight off their fathers? Explain your reasoning. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



2.	When a Thomson's gazelle detects a nearby stalking cheetah, the gazelle often begins bouncing up and down with a stiff-legged gait called stotting (see Figure 11.24 on page 450 in your textbook). One hypothesis is that stotting has evolved because it may help alert the gazelle's kin to the presence of a predator, analogous to the alarm calls of ground squirrels. Caro reports that stotting does not seem to increase the gazelle's risk of being attacked. In fact, once a gazelle begins to stott, the cheetah often gives up the hunt. How is C (the cost of stotting) different for a gazelle, compared to C (the cost of alarm calls) for a ground squirrel? Do you think it is likely that stotting is an altruistic behavior? With this in mind, make a prediction about whether a gazelle will stott when there are no other gazelles around, and then look up Caro's papers to see if you are right. Caro, T. M. 1986. The function of stotting in Thomson's gazelles: Some tests of the hypotheses. Animal Behaviour 34: 663–684. Caro, T. M. 1994. Ungulate antipredator behaviour: Preliminary and comparative data from African bovids. Behaviour 128: 189–228. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



3.	The cubs of spotted hyenas often begin fighting within moments of birth, and often one hyena cub dies. The mother hyena does not interfere. How could such a behavior have evolved? For instance, from the winning sibling's point of view, what must B (benefit of siblicide) be, relative to C (cost of siblicide), to favor the evolution of siblicide? From the parent's point of view, what must B be, relative to C, for the parent to watch calmly rather than to interfere? For more about the unusual social system of spotted hyenas and for new information from studies of wild hyenas, see: Frank, Laurence G. 1997. Evolution of genital masculinization: Why do female hyaenas have such a large 'penis'? Trends in Ecology and Evolution 12: 58–62. Golla, W., H. Hofer, and M. L. East. 1999. Within-litter sibling aggression in spotted hyaenas: Effect of maternal nursing, sex and age. Animal Behaviour 58: 715–726. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



4.	Blue jays (Cyanocitta cristata) seem to be better than American robins (Turdus migratorius) at recognizing individuals. In one study, blue jays raised with American robins could distinguish strange from familiar robins better than the robins themselves. Do you think these species differ in occurrence of kin selection or reciprocal altruism (or both)? Why? See: Schimmel, K. L, and F. E. Wasserman. 1994. Individual and species preference in two passerine birds: Auditory and visual cues. Auk 111: 634–642. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



5.	The first paragraph of this chapter refers to crows who cooperate in chasing a predator away (a behavior known as mobbing) and who help their parents raise their siblings. Which behavior is mutualistic, and which behavior is favored by kin selection? Suggest a hypothesis to explain why young crows in some populations might help at the nest, while in other populations they nest on their own. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



6.	The biologist J. B. S. Haldane was once explaining kin selection to some friends in a pub. As the story goes, he scribbled some calculations on an envelope and announced that he would be willing to die for two brothers or eight cousins. Explain his reasoning. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



7.	Look at Figure 11.18 (page 440 in your textbook) on parent–offspring conflict. Explain, in general terms, why the behavior of females should evolve so that mothers start weaning when B/C falls below 1. (Hint: Consider the reproductive success of mothers who wean very early and of mothers who wean very late.) If a mother could have only one litter of young in her lifetime, how would the period of weaning conflict change? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



8.	The text claims that eusociality has evolved several times independently within the hymenoptera. What is the evidence for this statement? If it is true, in what sense is eusociality in ants, bees, and wasps an example of convergent evolution (see Chapter 14)? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



9.	How would you go about testing the hypothesis that female lions who do not participate in territory defense reciprocate by providing milk to the offspring of territory defenders? List the predictions made by the hypothesis and the types of data you would have to collect. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



10.	House sparrows often produce two successive broods of young. Males feed their first brood only briefly, but feed their second brood for much longer. Why do males feed first broods less than second broods? (Hint: Consider how C, the cost of feeding the current brood, changes.) How could you test your hypothesis? How is this situation analogous to weaning conflict in mammals? See: Hegner, R. E., and J. C. Wingfield. 1986. Behavioral and endocrine correlates of multiple brooding in the semicolonial house sparrow Passer domesticus. I. Males. Hormones and Behavior 20: 294–312. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



11.	Which is more common in human cultures—eusociality (look back at the three requirements of eusociality; can you think of any human cultures that fit?), or a helper-at-the-nest social system? Which do you think is generally more common in social animals? Why? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



12.	Human siblings often show intense sibling rivalry that typically declines during the teenage years. Suggest an evolutionary explanation for this pattern. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

Chapter 11: Kin Selection and Social Behavior

Further Thought