section_path: Physiological behavior
section_name: Physiological behavior
paragraph_text: Physiological behavior
  
  Humans undergo many behaviors common to animals to support the processes of the human body. Humans eat food to obtain nutrition. These foods may be chosen for their nutritional value, but they may also be eaten for pleasure. Eating often follows a food preparation process to make it more enjoyable. Humans dispose of waste through urination and defecation. Excrement is often treated as taboo, particularly in developed and urban communities where sanitation is more widely available and excrement has no value as fertilizer. Humans also regularly engage in sleep, based on homeostatic and circadian factors. The circadian rhythm causes humans to require sleep at a regular pattern and is typically calibrated to the day-night cycle and sleep-wake habits. Homeostasis is also maintained, causing longer sleep longer after periods of sleep deprivation. The human sleep cycle takes place over 90 minutes, and it repeats 3–5 times during normal sleep.
  
  There are also unique behaviors that humans undergo to maintain physical health. Humans have developed medicine to prevent and treat illnesses. In industrialized nations, eating habits that favor better nutrition, hygienic behaviors that promote sanitation, medical treatment to eradicate diseases, and the use of birth control significantly improve human health. Humans can also engage in exercise beyond that required for survival to maintain health. Humans engage in hygiene to limit exposure to dirt and pathogens. Some of these behaviors are adaptive while others are learned. Basic behaviors of disgust evolved as an adaptation to prevent contact with sources of pathogens, resulting in a biological aversion to feces, body fluids, rotten food, and animals that are commonly disease vectors. Personal grooming, disposal of human corpses, use of sewerage, and use of cleaning agents are hygienic behaviors common to most human societies.
  
  Humans reproduce sexually, engaging in sexual intercourse for both reproduction and sexual pleasure. Human reproduction is closely associated with human sexuality and an instinctive desire to procreate, though humans are unique in that they intentionally control the number of offspring that they produce. Humans engage in a large variety of reproductive behaviors relative to other animals, with various mating structures that include forms of monogamy, polygyny, and polyandry. How humans engage in mating behavior is heavily influenced by cultural norms and customs. Unlike most mammals, human women ovulate spontaneously rather than seasonally, with a menstrual cycle that typically lasts 25–35 days.
  
  Humans are bipedal and move by walking. Human walking corresponds to the bipedal gait cycle, which involves alternating heel contact and toe off with the ground and slight elevation and rotation of the pelvis. Balance while walking is learned during the first 7–9 years of life, and individual humans develop unique gaits while learning to displace weight, adjust center of mass, and coordinate neural control with movement. Humans can achieve higher speed by running. The endurance running hypothesis proposes that humans can outpace most other animals over long distances through running, though human running causes a higher rate of energy exertion. The human body self-regulates through perspiration during periods of exertion, allowing humans more endurance than other animals. The human hand is prehensile and capable of grasping objects and applying force with control over the hand's dexterity and grip strength. This allows the use of complex tools by humans.