The media report numerous claims and counterclaims about the benefits and dangers of certain foods, dietary supplements, and diets. Have you modified your eating habits on the basis of nutritional information disseminated by the media? Why or why not? How should we evaluate whether such nutritional claims are valid?

How might our craving for fatty foods, which is helping to fuel the obesity crisis, have evolved through natural selection?

Among vertebrates, the large intestine exists only in lineages that are primarily terrestrial (amphibians, reptiles, and mammals). Propose a hypothesis to explain this observation.

One common piece of dieting advice is to replace energy-dense food with nutrient-dense food. What does this mean?

Minnows are mainly carnivorous, eating insects and other small animals. However, herbivory has evolved independently in minnows several times. What changes in digestive structure and function are associated with the evolution of herbivory?Like cichlids, minnows use their pharyngeal jaws to process food. Suggest some possible structural differences between the teeth on the pharyngeal jaws of carnivorous and herbivorous minnows.

Minnows are mainly carnivorous, eating insects and other small animals. However, herbivory has evolved independently in minnows several times. What changes in digestive structure and function are associated with the evolution of herbivory?Which of the following is true of the digestive tracts of minnows?a. They are incomplete but have both a mouth and an anus.b. They are complete, facilitating compartmentalization of digestion in different organs.c. They are incomplete, with no accessory organs.d. They are complete and include a large gastrovascular cavity.

It is estimated that 15% of Americans do not always have access to enough food. Worldwide, more than 1 billion people go to bed hungry most nights, and millions of people have starved to death in recent decades. In some cases, war, poor crop yields, and disease epidemics strip people of food. Many say instead that it is not inadequate food production but unequal food ­distribution that causes food shortages. What responsibility do nations have for feeding their citizens? For feeding the people of other countries? What do you think you can do to lessen world hunger?

Minnows are mainly carnivorous, eating insects and other small animals. However, herbivory has evolved independently in minnows several times. What changes in digestive structure and function are associated with the evolution of herbivory?Researchers compared the relative gut length—the length of the digestive tract divided by body length—in four species of herbivorous minnows and four species of carnivorous minnows. The results are shown in the graph provided here. Based on these data, what conclusion can you draw about the relationship between diet and gut length?

SCIENTIFIC THINKING Consider the relationship between ­correlation and causation with respect to some pairs of human traits. For example, are freckles and red hair correlated? Is there causation? How does this concept relate to the study of human nutrition? Can you name examples of correlation in humans with respect to obesity? Explain each answer.