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Monkeys, Apes and Humans
Anthropology 1500
Department of Anthropology, University of Missouri-Columbia

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First draft due 12:30 PM Tuesday, Feb 22

Final draft due 12:30 PM Tuesday Feb 29

Question: What factors are associated with Sexual Dimorphisms ("SDs") among primates? Use the "primate data sheets" (available at MAH website) to explore and then test possible associations using the comparative method. For example, you might want to examine relations between: diet and SDs, mating system and SDs, parental care and SDs, predation and SDs, body size and SDs, terrestrial vs. arboreal and SDs etc. For this quiz I want you to test at least two hypotheses. You might want to explore multiple (complex) relations among variables, e.g., mating system, diet, and SDs. Your study should begin with hypotheses that explain why certain factors should be related to sexual dimorphism. For example: "sexual dimorphism allows males to protect the group from predators, and hence is more likely when predation rates are high." (note this is just an example; develop your own hypotheses). There are different ways to measure SD; for example, you could use body weight or length, or some other character, such as canine size, but I recommend using male body weight/female body weight for this quiz because those data are the most complete and easy to deal with.

Structure: Your three -page double space essay should follow the format explained in the "paper organization" handout. The "audience" for your paper is an intelligent reader that does not know much about primates or the topic of sexual dimorphism, for example, an educated friend. Begin with an introductory paragraph that contains a topic sentence that summarizes the main point of your essay. Underline your topic sentence. Then follow with the body of your essay, and finish with a summary paragraph. You may use a table(s) to summarize data relations (highly recommended-figures or tables are useful for this assignment). Your first draft will be edited, graded (50 pts), and returned to you. You will then rewrite your essay and turn in a final version (100 pts.).

Hints: Work hard! You can do this well!

Stage I. Collect your thoughts on how natural selection acts on sexual dimorphisms. Read chap 7 in Boyd and Silk. Decide what factors you want to investigate are associated with SD, based on evolutionary logic. That is, formulate your hypotheses. You should have an explanation for why you think the factors you choose are likely to be relevant to understanding SD. Do not worry about choosing a factor that ends up not being associated with SD; it is as important to determine what factors are not associated with SD as it is to determine what factors are. Choose factors that you will be able to get good information about from your primate fact sheets.

Stage II. Compute a measure of sexual dimorphism (male/female body weight) from the data sheets. Compute a measure of your other variables (e.g., diet, body size, mating systemů.). Analyze data to test for associations between body weight SD (dependent variable) and the factors predicted to favor SD (independent variable).

Stage III. Organize your essay. (1) Explain what sexual dimorphism is. (2) State your hypotheses. (3) Explain what each hypothesis predicts. (4) Explain what your measures/data are. (5) Make a table(s) showing relations among variables considered by your hypotheses. (6) Explain how the data fit or do not fit predictions from each hypothesis. (7) Exceptional essays will suggest further experiments, observations, or field studies that would help resolve controversies suggested by your study. Are there other species (not in the handout data set) that would provide good "test cases" for your predictions? How does your group's species fit in?


Ringtail Lemur

Ringtail Lemur

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