Final answer:
Humans require a large number of calories due to a high metabolic rate and the need to maintain a constant body temperature. Carbohydrates, proteins, and fats provide different amounts of energy. Human males have a BMR of 1600 to 1800 kcal/day, and females have a BMR of 1300 to 1500 kcal/day.
Step-by-step explanation:
Humans, as mammals, require a large number of calories compared to other species due to several factors. One major factor is our high metabolic rate, which requires a lot of energy. Maintaining a constant body temperature also requires extensive energy. Additionally, smaller endothermic animals, like humans, have a higher basal metabolic rate per body weight compared to larger animals.
Carbohydrates and proteins contain about 4.5 to 5 kcal/g, while fat contains about 9 kcal/g. The metabolic rate is estimated as the basal metabolic rate (BMR) in endothermic animals at rest. Human males have a BMR of 1600 to 1800 kcal/day, and human females have a BMR of 1300 to 1500 kcal/day.
Overall, our need for a large number of calories is essential to support our high metabolic rate, maintain body temperature, and provide energy for everyday activities.