Bodies. Changing Body Shapes and Sizes Short bodies, long guts By 6 million years ago Australopithecus afarensis, "Lucy", reconstructed skeleton The earliest human species were small in size and usually had long arms and short legs. Their plant-based diet required a large digestive tract. A wide rib cage made room for the stomach, intestines, and other organs that break down food. Tall bodies, short guts By 1.9 million years ago As some early humans adapted to hot climates, they evolved narrow bodies that helped them stay cool.
Compact bodies, short guts By 400,000 years ago When early humans spread to colder climates, their body shapes evolved in ways that helped them stay warm. Adapted to Hot Climates This is the skeleton of an eight- to nine-year-old Homo erectus boy who lived in East Africa about 1.6 million years ago. Narrow body Notice the narrow pelvis of this species. Long legs The lower legs of Homo erectus were long, a feature that helped dissipate heat. Adapted to Cold Climates Broad body. Blood Flow and Thermoregulation | Science. Size. Untitled. Basal metabolic rate. Basal metabolic rate (BMR), and the closely related resting metabolic rate (RMR), is the rate of energy expenditure by humans and other animals at rest, and is measured in kJ per hour per kg body mass. Rest is defined as existing in a neutrally temperate environment while in the post-absorptive state.
In plants, different considerations apply. The release, and using, of energy in this state is sufficient only for the functioning of the vital organs, the heart, lungs, nervous system, kidneys, liver, intestine, sex organs, muscles, and skin. Description[edit] The body's generation of heat is known as thermogenesis and it can be measured to determine the amount of energy expended. BMR generally decreases with age and with the decrease in lean body mass (as may happen with aging). Increasing muscle mass increases BMR, although the effect is not significant enough to act as a weight-loss method. Indirect calorimetry laboratory with canopy hood (dilution technique) Physiology[edit] Glucose[edit]
Metabolism Calculator.