Human

Age

A newborn is helpless and depends on its parents for a long time: children usually take their first steps at 9–18 months, and puberty takes place at about 10–16 years. Growth continues until 18–20 years of age. Average life expectancy in most countries is 70–85 years, and many people live to 90–100. The longest documented lifespan is 122 years, and scientists estimate the theoretical limit of human lifespan at roughly 120–150 years.

Phenotype

The human body lacks a dense coat of hair: visible hair grows mainly on the head and, in adults, under the arms, in the groin and on the face in men. Skin colour ranges from very light to dark brown, hair from blond to black, and eyes from blue and grey to brown. The face is flat with a protruding nose and chin and a high forehead. The arms are noticeably shorter than the legs.

Physiology

An average adult is about 1.6–1.8 m tall and usually weighs 55–85 kg; men are on average taller and heavier than women. Humans walk on two legs, have an upright posture, an opposable thumb and a brain of about 1,300–1,400 cm³. Normal adult oral body temperature is about 36.1–37.2 °C: rectal readings are 0.3–0.5 °C higher, armpit readings lower, it is lower in the morning than in the evening, and it also depends on age, activity and hormones. 37.3–38 °C is considered low-grade, from 38 °C a fever, 39–41 °C a high fever, and 41 °C and above hyperpyrexia, a medical emergency. When core temperature drops to 35 °C or below, hypothermia develops: mild at 32–35 °C, moderate at 28–32 °C and severe below 28 °C, with heart rhythm disturbances, coma and risk of death, although active rewarming can sometimes save the person.

Habitat

Humans live in almost every land environment, from tropical forests and savannas to steppes, deserts, high mountains and Arctic tundra. Clothing, fire and shelter allowed them to settle in very different climates. Today more than half of all people live in cities, the rest in rural areas.

Humans build permanent dwellings, from huts, yurts and igloos to wooden and stone houses and multi-storey buildings. A dwelling protects from bad weather, cold and heat and is used for sleeping, cooking and raising children. In ancient times people also used caves and shelters made of branches and hides.

Geography

The species originated in Africa about 300,000 years ago and later spread to every continent. Today people live permanently on all continents except Antarctica, where only research stations operate. The world population exceeds 8 billion, and most people live in Asia.

Feeding

Humans are omnivores: their diet includes grains, vegetables, fruit, legumes, nuts, meat, fish, eggs and dairy products. Most food is cooked, and diet varies greatly by region and culture; an adult needs about 2,000–2,500 kcal and roughly 1.5–2 litres of water a day. Many religions restrict food. In Islam (halal), beef, mutton, goat, camel, chicken and most fish are permitted when slaughtered ritually, while pork, carrion, blood, predatory animals and alcohol are forbidden. In Judaism (kashrut), meat of ruminants with split hooves — cattle, sheep, goats, deer — certain birds such as chicken, duck, goose and turkey, and fish with fins and scales are permitted, while pork, rabbit, shellfish and mixing meat with milk are forbidden. Hindus do not eat beef and many are vegetarian, Jains follow strict vegetarianism, and many Buddhists avoid meat. There are also fasts: Ramadan in Islam, Yom Kippur and other fasts in Judaism, and Lent among Orthodox, Catholic and other Christians. Regardless of religion, doctors do not recommend alcohol: it is toxic and carcinogenic, and according to the WHO there is no safe dose. Excess salt, sugar and trans fats, processed meat and large amounts of red meat are also harmful. Raw or undercooked meat and eggs, raw milk, spoiled food and poisonous mushrooms and plants are dangerous.

Reproduction

Pregnancy lasts about 9 months (roughly 280 days). Usually a single child is born; twins occur in about 1–2% of births. The child remains in its parents' care for a long time and becomes an adult only by 16–20 years of age. Reproduction is not tied to a season.

The leading causes of death worldwide are diseases of the heart and blood vessels, above all ischaemic heart disease and stroke. They are followed by cancers, chronic lung diseases, diabetes, kidney disease and dementia. Infections — respiratory and intestinal infections, tuberculosis, HIV and malaria — remain a major threat, especially in poorer countries. Not smoking or drinking alcohol, physical activity, a healthy diet, vaccination and regular medical check-ups help reduce the risk.

Humans are a highly social species: they live in families and complex communities, from small groups to states. People communicate through articulate speech — there are about 7,000 languages in the world — and writing. Humans make and use complex tools, pass knowledge and customs on to the next generations and create art, science and technology. They are mostly active during the day, and adults need 7–9 hours of sleep a day.

In Husbandry

For a comfortable life humans need a dry, warm and ventilated dwelling. A comfortable indoor temperature is about 20–24 °C with a relative humidity of 40–60%. Access to clean drinking water, sanitation and daylight is important. The minimum living space for one person is estimated at 9–12 m², while a comfortable life requires about 30–40 m² per person.